ASN RSS https://amnat.org/ Latest press releases and announcements from the ASN en-us Thu, 20 Sep 2018 05:00:00 GMT 60 Call for Symposium Proposals for Evolution 2019 in Providence, Rhode Island https://amnat.org/announcements/CallSympASN2018.html The American Society of Naturalists invites proposals for a special symposium at the 2019 annual joint meeting of the Society for the Study of Evolution, the American Society of Naturalists, and the Society of Systematic Biologists, to be held June 21-25, 2019, in Providence, RI. Proposed symposium topics should support the Society’s goal to advance the conceptual unification of the biological sciences and further knowledge in evolution, ecology, behavior, and organismal biology. Proposals should be synthetic and interdisciplinary, and address important emerging issues in evolution, ecology, or behavior. A budget of $8,000 for travel, registration, and accommodation is provided to help defray expenses. Proposals should include (1) a title; (2) a description of the symposium topic (one page); (3) a list of six speakers, including institutional affiliations, who have agreed to participate in the symposium; (4) a justification for the symposium explaining why the topic and speakers are appropriate for a Society-sponsored symposium (up to one page). Please submit proposals by midnight Eastern Standard Time on November 1, 2018, by email (kmkay@ucsc.edu) as a single pdf attachment, under subject heading: ASN Symposium Proposal: Evolution 2019. Proposals that include women, young investigators, and individuals from underrepresented groups are especially encouraged. The Society’s selection committee will evaluate proposals based on the significance and timeliness of the topic, and on it differing substantively from recent symposia sponsored by the Society. All applicants will be notified of the decision before the end of December. Kathleen M. Kay ASN Symposium Committee Chair Department of Ecology and Evolutionary Biology University of California, Santa Cruz kmkay@ucsc.edu <p>The American Society of Naturalists invites proposals for a special symposium at the 2019 annual joint meeting of the Society for the Study of Evolution, the American Society of Naturalists, and the Society of Systematic Biologists, to be held June 21-25, 2019, in Providence, RI.</p> <p>Proposed symposium topics should support the Society&rsquo;s goal to advance the conceptual unification of the biological sciences and further knowledge in evolution, ecology, behavior, and organismal biology. Proposals should be synthetic and interdisciplinary, and address important emerging issues in evolution, ecology, or behavior. A budget of $8,000 for travel, registration, and accommodation is provided to help defray expenses.</p> <p>Proposals should include (1) a title; (2) a description of the symposium topic (one page); (3) a list of six speakers, including institutional affiliations, who have agreed to participate in the symposium; (4) a justification for the symposium explaining why the topic and speakers are appropriate for a Society-sponsored symposium (up to one page).</p> <p>Please submit proposals by midnight Eastern Standard Time on November 1, 2018, by email (<a href="mailto:kmkay@ucsc.edu?subject=ASN%20Symposium%20Proposal%3A%20Evolution%202019">kmkay@ucsc.edu</a>) as a single pdf attachment, under subject heading: ASN Symposium Proposal: Evolution 2019. Proposals that include women, young investigators, and individuals from underrepresented groups are especially encouraged.</p> <p>The Society&rsquo;s selection committee will evaluate proposals based on the significance and timeliness of the topic, and on it differing substantively from recent symposia sponsored by the Society. All applicants will be notified of the decision before the end of December.</p> <p><br /> Kathleen M. Kay<br /> ASN Symposium Committee Chair<br /> Department of Ecology and Evolutionary Biology<br /> University of California, Santa Cruz<br /> <a href="mailto:kmkay@ucsc.edu?subject=ASN%20Symposium%20Proposal%3A%20Evolution%202019">kmkay@ucsc.edu</a></p> Mon, 17 Sep 2018 05:00:00 GMT “Space use and leadership modify dilution effects on optimal vigilance under food/safety trade-offs” https://amnat.org/an/newpapers/JanPatin.html The DOI will be https://dx.doi.org/10.1086/700566 Decision-making on space use matters! A model of interacting antipredator strategies: vigilance, grouping, and space use Most animals live under predation risk, and adjust their vigilance to the level of risk they perceive. When living in group, individuals benefit from a “dilution” effect, by which their own risk is reduced by the presence of the other group members that could also be targeted by the predator. Many models of evolution of anti-predator behaviours have focused on the interaction between vigilance and group size, and have always suggested that vigilance should decrease with increasing group size. This is commonly observed, but not always. And animals also adjust predation risk by foraging in areas that they perceive as less risky. In a new article appearing in The&nbsp;American Naturalist, Rémi Patin and colleagues propose a model, designed with social species such as primates or equids in mind, to study the interactions between vigilance, group size, and space use. The model assumes that, within groups, a leader takes all space use decisions for the rest of the group made up of followers. In this situation, the relationship between vigilance and group size becomes complex. Vigilance does not always decrease with group size, because the leader may favor using riskier and richer areas over becoming less vigilant. Followers are less vigilant than the leader, because they need to compensate for uncertainties in future foraging opportunities, and die from predation more often. Overall, followers still benefit from group living, but less than the leader. Leaders might gain more by remaining leaders than by becoming followers in a larger group. These results might therefore explain the apparently paradoxical observation made in some species, such as in equids, that a group leader would reject a potential new group member despite the dilution benefit the addition of the new individual would bring. Abstract Dilution of predation risk within groups allows individuals to be less vigilant and forage more while still facing lower risk than if they were alone. How group size influences vigilance when individuals can also adjust their space use, and whether this relationship differs among individuals contributing differently to space use decisions, remain unknown. We present a model-based study on how dilution affects the optimal anti-predator behavior of group members, in groups where all individuals determine their vigilance level, while group leaders also determine space use. We showed that optimal vigilance did not always decrease with group size, as it was sometimes favorable for individuals in larger groups to use riskier patches while remaining vigilant. Followers were also generally less vigilant than leaders. Indeed, followers needed to acquire more resources than leaders as only the latter could decide when to go to richer patches. Followers still benefit from dilution of predation risk compared to solitary individuals. For leaders, keeping their leadership status can be more important than incorporating new group members to increase dilution. We demonstrate that risk dilution impacts both optimal vigilance and space use, with fitness reward being tied to a member’s ability to influence group space use. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700566 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700566">Read the Article</a></i> </p> --> <p><b>Decision-making on space use matters! A model of interacting antipredator strategies: vigilance, grouping, and space use </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ost animals live under predation risk, and adjust their vigilance to the level of risk they perceive. When living in group, individuals benefit from a “dilution” effect, by which their own risk is reduced by the presence of the other group members that could also be targeted by the predator. Many models of evolution of anti-predator behaviours have focused on the interaction between vigilance and group size, and have always suggested that vigilance should decrease with increasing group size. This is commonly observed, but not always. And animals also adjust predation risk by foraging in areas that they perceive as less risky. In a new article appearing in <i>The&nbsp;American Naturalist</i>, Rémi Patin and colleagues propose a model, designed with social species such as primates or equids in mind, to study the interactions between vigilance, group size, and space use. The model assumes that, within groups, a leader takes all space use decisions for the rest of the group made up of followers. In this situation, the relationship between vigilance and group size becomes complex. Vigilance does not always decrease with group size, because the leader may favor using riskier and richer areas over becoming less vigilant. Followers are less vigilant than the leader, because they need to compensate for uncertainties in future foraging opportunities, and die from predation more often. Overall, followers still benefit from group living, but less than the leader. Leaders might gain more by remaining leaders than by becoming followers in a larger group. These results might therefore explain the apparently paradoxical observation made in some species, such as in equids, that a group leader would reject a potential new group member despite the dilution benefit the addition of the new individual would bring. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">D</span>ilution of predation risk within groups allows individuals to be less vigilant and forage more while still facing lower risk than if they were alone. How group size influences vigilance when individuals can also adjust their space use, and whether this relationship differs among individuals contributing differently to space use decisions, remain unknown. We present a model-based study on how dilution affects the optimal anti-predator behavior of group members, in groups where all individuals determine their vigilance level, while group leaders also determine space use. We showed that optimal vigilance did not always decrease with group size, as it was sometimes favorable for individuals in larger groups to use riskier patches while remaining vigilant. Followers were also generally less vigilant than leaders. Indeed, followers needed to acquire more resources than leaders as only the latter could decide when to go to richer patches. Followers still benefit from dilution of predation risk compared to solitary individuals. For leaders, keeping their leadership status can be more important than incorporating new group members to increase dilution. We demonstrate that risk dilution impacts both optimal vigilance and space use, with fitness reward being tied to a member’s ability to influence group space use.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Sep 2018 05:00:00 GMT “Sexual conflict and STIs: coevolution of sexually antagonistic host traits with a sexually transmitted infection” https://amnat.org/an/newpapers/JanWardlaw-A.html The DOI will be https://dx.doi.org/10.1086/700564 Abstract In many taxa, there is a conflict between the sexes over mating rate. The outcome of sexually antagonistic coevolution depends on the costs of mating and natural selection against sexually antagonistic traits. A sexually transmitted infection (STI) changes the relative strength of these costs. We study the three-way evolutionary interaction between male persistence, female resistance, and STI virulence for two types of STIs: a viability-reducing STI and a reproduction-reducing STI. A viability-reducing STI escalates conflict between the sexes. This leads to increased STI virulence (i.e., full coevolution) if the costs of sexually antagonistic traits occur through viability but not if the costs occur through reproduction. In contrast, a reproduction-reducing STI de-escalates the sexual conflict but STI virulence does not coevolve in response. We also investigated the establishment probability of STIs under different combinations of evolvability. Successful invasion by a viability-reducing STI becomes less likely if hosts (but not parasite) are evolvable, especially if only the female trait can evolve. A reproduction-reducing STI can almost always invade because it does not kill its host. We discuss how the evolution of host and parasite traits in a system with sexual conflict differs from a system with female mate choice. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700564 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700564">Read the Article</a></i> </p> --><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n many taxa, there is a conflict between the sexes over mating rate. The outcome of sexually antagonistic coevolution depends on the costs of mating and natural selection against sexually antagonistic traits. A sexually transmitted infection (STI) changes the relative strength of these costs. We study the three-way evolutionary interaction between male persistence, female resistance, and STI virulence for two types of STIs: a viability-reducing STI and a reproduction-reducing STI. A viability-reducing STI escalates conflict between the sexes. This leads to increased STI virulence (i.e., full coevolution) if the costs of sexually antagonistic traits occur through viability but not if the costs occur through reproduction. In contrast, a reproduction-reducing STI de-escalates the sexual conflict but STI virulence does not coevolve in response. We also investigated the establishment probability of STIs under different combinations of evolvability. Successful invasion by a viability-reducing STI becomes less likely if hosts (but not parasite) are evolvable, especially if only the female trait can evolve. A reproduction-reducing STI can almost always invade because it does not kill its host. We discuss how the evolution of host and parasite traits in a system with sexual conflict differs from a system with female mate choice.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Sep 2018 05:00:00 GMT “An empirical and mechanistic explanation of abundance-occupancy relationships for a critically endangered nomadic migrant” https://amnat.org/an/newpapers/JanWebb.html The DOI will be https://dx.doi.org/10.1086/700595 Abundance-occupancy relationships for a nomadic migrant are explained by variations in food abundance A&nbsp;positive abundance–occupancy relationship (AOR) is a pervasive pattern in macroecology implying species with larger geographic distributions are generally more locally abundant. But for species tracking variable resources in space and time, this is not always the case. This study by the Difficult Bird Research Group provides a rare empirical example of a negative AOR for the nomadic critically endangered swift parrot caused by dynamic pulses in the availability and location of food over seven years (2009–2015). In their breeding range (Tasmania, Australia), local densities of birds increased as food availability decreased, and vice versa. Although this study was conducted on a highly mobile species over a large geographic area, the results are likely relevant to partial migrants and less mobile species when their resources vary over smaller scales. This highlights the need to carefully consider the appropriate scales of sampling for AOR studies. Similarly, the association between the probability of occurrence and abundance is usually assumed to be positive and constant for species distribution models (SDMs). For the swift parrot, this relationship was positive but non-linear and varied with scale and between years due to differing degrees of spatial aggregation caused by changing food availability. Importantly, the results show that high abundance (or occupancy) does not necessarily equate to high quality habitat. Contrasting these two areas of research (i.e. SDMs and AORs) allows better identification of fluctuations in carrying capacity, priority sites, resource bottlenecks, and interpretation of dynamic SDMs. Further, understanding the causal mechanisms of AORs and how they change over time may provide an empirical means to understand changes in population size and range dynamics in variable environments. Abstract The positive abundance-occupancy relationship (AOR) is a pervasive pattern in macroecology. Similarly, the association between occupancy (or probability of occurrence) and abundance is also usually assumed to be positive and in most cases constant. Examples of AORs for nomadic species with variable distributions are extremely rare. Here we examined temporal and spatial trends in the AOR over seven years for a critically endangered nomadic migrant which relies on dynamic pulses in food availability to breed. We predicted a negative temporal relationship, where local mean abundances increase when the number of occupied sites decreases, and a positive relationship between local abundances and the probability of occurrence. We also predicted that these patterns are largely attributable to spatiotemporal variation in food abundance. The temporal AOR was significantly negative and annual food availability was significantly positively correlated with the number of occupied sites, but negatively correlated with abundance. Thus, as food availability decreased, local densities of birds increased, and vice-versa. The abundance – probability of occurrence relationship was positive and non-linear, but varied between years due to differing degrees of spatial aggregation caused by changing food availability. Importantly, high abundance (or occupancy) did not necessarily equate to high quality habitat and may be indicative of resource bottlenecks or exposure to other processes affecting vital rates. Our results provide a rare empirical example that highlights the complexity of AORs for species that target aggregated food resources in dynamic environments. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700595 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700595">Read the Article</a></i> </p> --> <p><b>Abundance-occupancy relationships for a nomadic migrant are explained by variations in food abundance </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>&nbsp;positive abundance–occupancy relationship (AOR) is a pervasive pattern in macroecology implying species with larger geographic distributions are generally more locally abundant. But for species tracking variable resources in space and time, this is not always the case. This study by the Difficult Bird Research Group provides a rare empirical example of a negative AOR for the nomadic critically endangered swift parrot caused by dynamic pulses in the availability and location of food over seven years (2009–2015). In their breeding range (Tasmania, Australia), local densities of birds increased as food availability decreased, and vice versa. </p><p>Although this study was conducted on a highly mobile species over a large geographic area, the results are likely relevant to partial migrants and less mobile species when their resources vary over smaller scales. This highlights the need to carefully consider the appropriate scales of sampling for AOR studies. Similarly, the association between the probability of occurrence and abundance is usually assumed to be positive and constant for species distribution models (SDMs). For the swift parrot, this relationship was positive but non-linear and varied with scale and between years due to differing degrees of spatial aggregation caused by changing food availability. Importantly, the results show that high abundance (or occupancy) does not necessarily equate to high quality habitat. </p><p>Contrasting these two areas of research (i.e. SDMs and AORs) allows better identification of fluctuations in carrying capacity, priority sites, resource bottlenecks, and interpretation of dynamic SDMs. Further, understanding the causal mechanisms of AORs and how they change over time may provide an empirical means to understand changes in population size and range dynamics in variable environments.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he positive abundance-occupancy relationship (AOR) is a pervasive pattern in macroecology. Similarly, the association between occupancy (or probability of occurrence) and abundance is also usually assumed to be positive and in most cases constant. Examples of AORs for nomadic species with variable distributions are extremely rare. Here we examined temporal and spatial trends in the AOR over seven years for a critically endangered nomadic migrant which relies on dynamic pulses in food availability to breed. We predicted a negative temporal relationship, where local mean abundances increase when the number of occupied sites decreases, and a positive relationship between local abundances and the probability of occurrence. We also predicted that these patterns are largely attributable to spatiotemporal variation in food abundance. The temporal AOR was significantly negative and annual food availability was significantly positively correlated with the number of occupied sites, but negatively correlated with abundance. Thus, as food availability decreased, local densities of birds increased, and vice-versa. The abundance – probability of occurrence relationship was positive and non-linear, but varied between years due to differing degrees of spatial aggregation caused by changing food availability. Importantly, high abundance (or occupancy) did not necessarily equate to high quality habitat and may be indicative of resource bottlenecks or exposure to other processes affecting vital rates. Our results provide a rare empirical example that highlights the complexity of AORs for species that target aggregated food resources in dynamic environments. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Sep 2018 05:00:00 GMT “Fitness consequences of female alternative reproductive tactics in house mice (Mus musculus domesticus)” https://amnat.org/an/newpapers/JanFerrari.html The DOI will be https://dx.doi.org/10.1086/700567 Female house mice are known to raise their young either alone, or together with one or more other mothers in a communal nest. In the latter case, the mothers all care for the young indiscriminately. Whenever two alternative breeding tactics occurring in the same sex and population in nature are found, the question arises of how they can be evolutionarily stable. Manuela Ferrari and her colleagues at the University of Zurich (Anna Lindholm and Barbara König) studied communal and solitary breeding in a population of free-living house mice during a five year period (2007–2011). They find that females are more successful if they rear their litters solitarily, because pups in communal nests suffer from a lower survival probability. Why does communal breeding occur in the population, and at high rates (70%), if it reduces female fitness? The researchers show that older – likely also heavier and more experienced – females are less likely to rear their litters communally and instead have more solitary litters. Rearing young in a communal nest might therefore be a tactic that is followed only by females of lower overall condition. Such females might be either unable to rear litters on their own or to monopolize a nesting site and therefore take the least bad option, which is communal breeding instead of not breeding at all. These findings can help us to understand how behaviors that seem to have a cost, such as communal breeding in this example, can still be seen in nature if they are the best an individual can do in a given condition and situation. Abstract Alternative reproductive tactics are defined as discrete differences in morphological, physiological and/or behavioral traits associated with reproduction, which occur within the same sex and population. House mice provide a rare example for alternative reproductive tactics in females, which can either rear their young solitarily, or together with one or several other females in a communal nest. We assessed the fitness consequences of communal and solitary breeding in a wild population to understand how the two tactics can be evolutionarily stable. Females switched between the two tactics (with more than 50% of all females having two or more litters using both tactics), pointing towards communal and solitary breeding being two tactics within a single strategy and not two genetically determined strategies. Communal breeding resulted in reduced pup survival and negatively impacted female reproductive success. Older and likely heavier females more often reared their litters solitarily, indicating that females use a condition dependent strategy. Solitary breeding seems the more successful tactic and only younger and likely less competitive females might opt for communal nursing, even at the cost of increased pup mortality. This study emphasizes the importance of analyzing phenotypic plasticity and its role in cooperation in the context of female ARTs. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700567 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700567">Read the Article</a></i> </p> --><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">F</span>emale house mice are known to raise their young either alone, or together with one or more other mothers in a communal nest. In the latter case, the mothers all care for the young indiscriminately. Whenever two alternative breeding tactics occurring in the same sex and population in nature are found, the question arises of how they can be evolutionarily stable. Manuela Ferrari and her colleagues at the University of Zurich (Anna Lindholm and Barbara König) studied communal and solitary breeding in a population of free-living house mice during a five year period (2007–2011). They find that females are more successful if they rear their litters solitarily, because pups in communal nests suffer from a lower survival probability. Why does communal breeding occur in the population, and at high rates (70%), if it reduces female fitness? </p> <p>The researchers show that older – likely also heavier and more experienced – females are less likely to rear their litters communally and instead have more solitary litters. Rearing young in a communal nest might therefore be a tactic that is followed only by females of lower overall condition. Such females might be either unable to rear litters on their own or to monopolize a nesting site and therefore take the least bad option, which is communal breeding instead of not breeding at all. These findings can help us to understand how behaviors that seem to have a cost, such as communal breeding in this example, can still be seen in nature if they are the best an individual can do in a given condition and situation. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>lternative reproductive tactics are defined as discrete differences in morphological, physiological and/or behavioral traits associated with reproduction, which occur within the same sex and population. House mice provide a rare example for alternative reproductive tactics in females, which can either rear their young solitarily, or together with one or several other females in a communal nest. We assessed the fitness consequences of communal and solitary breeding in a wild population to understand how the two tactics can be evolutionarily stable. Females switched between the two tactics (with more than 50% of all females having two or more litters using both tactics), pointing towards communal and solitary breeding being two tactics within a single strategy and not two genetically determined strategies. Communal breeding resulted in reduced pup survival and negatively impacted female reproductive success. Older and likely heavier females more often reared their litters solitarily, indicating that females use a condition dependent strategy. Solitary breeding seems the more successful tactic and only younger and likely less competitive females might opt for communal nursing, even at the cost of increased pup mortality. This study emphasizes the importance of analyzing phenotypic plasticity and its role in cooperation in the context of female ARTs. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Sep 2018 05:00:00 GMT “From the past to the future: Considering the value and limits of evolutionary prediction” https://amnat.org/an/newpapers/JanShaw-A.html The DOI will be https://dx.doi.org/10.1086/700565 Abstract The complex interplay of the multiple genetic processes of evolution and the ecological contexts in which they proceed frustrates detailed identification of many of the states of populations, both past and future, that may be of interest. Prediction of rates of adaptation, in the sense of change in mean fitness, into the future would, however, valuably inform expectations for persistence of populations, especially in our era of rapid environmental change. Heavy investment in genomics and other molecular tools has fueled belief that those approaches can effectively predict adaptation into the future. I contest this view. Genome scans display the genomic footprints of the effects of natural selection and the other evolutionary processes over past generations, but it remains problematic to predict future change in mean fitness via genomic approaches. Here, I advocate for a direct approach to prediction of rates of ongoing adaptation. Following an overview of relevant quantitative genetic approaches, I outline the promise of the Fundamental Theorem of Natural Selection for study of the adaptive process. Empirical implementation of this concept can productively guide efforts both to deepen scientific insight about the process of adaptation and to inform measures for conserving the biota in the face of rapid environmental change. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700565 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700565">Read the Article</a></i> </p> --><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he complex interplay of the multiple genetic processes of evolution and the ecological contexts in which they proceed frustrates detailed identification of many of the states of populations, both past and future, that may be of interest. Prediction of rates of adaptation, in the sense of change in mean fitness, into the future would, however, valuably inform expectations for persistence of populations, especially in our era of rapid environmental change. Heavy investment in genomics and other molecular tools has fueled belief that those approaches can effectively predict adaptation into the future. I contest this view. Genome scans display the genomic footprints of the effects of natural selection and the other evolutionary processes over past generations, but it remains problematic to predict future change in mean fitness via genomic approaches. Here, I advocate for a direct approach to prediction of rates of ongoing adaptation. Following an overview of relevant quantitative genetic approaches, I outline the promise of the Fundamental Theorem of Natural Selection for study of the adaptive process. Empirical implementation of this concept can productively guide efforts both to deepen scientific insight about the process of adaptation and to inform measures for conserving the biota in the face of rapid environmental change. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Sep 2018 05:00:00 GMT “Delayed chemical defense: timely expulsion of herbivores reduces competition with neighboring plants” https://amnat.org/an/newpapers/JanBackmann.html The DOI will be https://dx.doi.org/10.1086/700577 Modeling shows that plants may use their herbivores to weaken competitors by delaying their defense reaction A&nbsp;plant faces several challenges in its life. It competes with neighboring plants for nutrients. At the same time, herbivores, such as caterpillars, want to eat it. Plants use chemical defenses to defend themselves against attackers. However, producing defense toxins is costly and slows the plant’s growth. Neighbors can easily outgrow a highly defended plant. Therefore, many plants use inducible defenses and produce defenses upon attack as a cost-saving strategy. However, there is a delay between the insect’s first bite and the plant’s defense response. In this time period, the plant is undefended and suffers feeding damage. Consequently, scientists had always assumed that natural selection should prefer small delay times. The authors of this study challenged this idea. This was motivated by the observation that caterpillars eat very little when they are small, whereas they consume 90% of all they eat in their entire lifetime in the last days before pupation. Therefore, it might be better to keep the small caterpillars. When they grow larger, and become more damaging, the defense should kick in. At that time, the plant should send the voracious caterpillar off – like a missile – to the neighbors. To explore this idea, the authors developed an individual-based model (Backmann, Grimm, Lin). They used experimental data from wild tobacco, Nicotiana attenuata, and its specialized herbivore, Manduca sexta from the lab (van Dam) and the field (Backmann, Baldwin). Using this model, the authors found that under strong competition and high herbivore pressure, the most efficient delay times were synchronized with the time the larvae need to grow large enough to severely damage neighboring plants. Based on this the authors concluded that being slow can be good, if the reaction is well-timed. Abstract Time delays in plant responses to insect herbivory are thought to be the principal disadvantage of induced over constitutive defenses, suggesting that there should be strong selection for rapid responses. However, observed time delays between the onset of herbivory and defense induction vary considerably among plants. We postulate that strong competition with conspecifics is an important co-determinant of the cost-benefit balance for induced responses. There may be a benefit to the plant to delay mounting a full defense response until the herbivore larvae are mobile enough to leave, and large enough to cause severe damage to neighboring plants. Thus, delayed responses could reduce the competitive pressure on the focal plant. To explore this idea, we developed an individual-based model using data from wild tobacco, Nicotiana attenuata, and its specialized herbivore, Manduca sexta. Chemical defense was assumed to be costly in terms of reduced plant growth. We used a genetic algorithm with the plant’s delay time as a heritable trait. A stationary distribution of delay times emerged, which under high herbivore densities peaked at higher values, which were related to the time larvae need to grow large enough to severely damage neighboring plants. Plants may thus tip the competitive balance by expelling insect herbivores to move to adjacent plants when the herbivores are most damaging. Thereby herbivores become part of a plant’s strategy for reducing competition and increasing fitness. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700577 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700577">Read the Article</a></i> </p> --> <p><b>Modeling shows that plants may use their herbivores to weaken competitors by delaying their defense reaction </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>&nbsp;plant faces several challenges in its life. It competes with neighboring plants for nutrients. At the same time, herbivores, such as caterpillars, want to eat it. Plants use chemical defenses to defend themselves against attackers. However, producing defense toxins is costly and slows the plant’s growth. Neighbors can easily outgrow a highly defended plant. Therefore, many plants use <i>inducible defenses and</i> produce defenses upon attack as a cost-saving strategy. However, there is a delay between the insect’s first bite and the plant’s defense response. In this time period, the plant is undefended and suffers feeding damage. Consequently, scientists had always assumed that natural selection should prefer small delay times. </p><p>The authors of this study challenged this idea. This was motivated by the observation that caterpillars eat very little when they are small, whereas they consume 90% of all they eat in their entire lifetime in the last days before pupation. Therefore, it might be better to keep the small caterpillars. When they grow larger, and become more damaging, the defense should kick in. At that time, the plant should send the voracious caterpillar off – like a missile – to the neighbors. </p><p>To explore this idea, the authors developed an individual-based model (Backmann, Grimm, Lin). They used experimental data from wild tobacco, <i>Nicotiana attenuata,</i> and its specialized herbivore, <i>Manduca sexta</i> from the lab (van Dam) and the field (Backmann, Baldwin). Using this model, the authors found that under strong competition and high herbivore pressure, the most efficient delay times were synchronized with the time the larvae need to grow large enough to severely damage neighboring plants. Based on this the authors concluded that being slow can be good, if the reaction is well-timed. </p> <hr /><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">T</span>ime delays in plant responses to insect herbivory are thought to be the principal disadvantage of induced over constitutive defenses, suggesting that there should be strong selection for rapid responses. However, observed time delays between the onset of herbivory and defense induction vary considerably among plants. We postulate that strong competition with conspecifics is an important co-determinant of the cost-benefit balance for induced responses. There may be a benefit to the plant to delay mounting a full defense response until the herbivore larvae are mobile enough to leave, and large enough to cause severe damage to neighboring plants. Thus, delayed responses could reduce the competitive pressure on the focal plant. To explore this idea, we developed an individual-based model using data from wild tobacco, <i>Nicotiana attenuata</i>, and its specialized herbivore, <i>Manduca sexta</i>. Chemical defense was assumed to be costly in terms of reduced plant growth. We used a genetic algorithm with the plant&rsquo;s delay time as a heritable trait. A stationary distribution of delay times emerged, which under high herbivore densities peaked at higher values, which were related to the time larvae need to grow large enough to severely damage neighboring plants. Plants may thus tip the competitive balance by expelling insect herbivores to move to adjacent plants when the herbivores are most damaging. Thereby herbivores become part of a plant&rsquo;s strategy for reducing competition and increasing fitness.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 12 Sep 2018 05:00:00 GMT “Metabolic theory and the temperature size rule explain the temperature dependence of population carrying capacity” https://amnat.org/an/newpapers/DecBernhardt.html The DOI will be https://dx.doi.org/10.1086/700114 Carrying capacity declines with warming, as predicted by the metabolic theory of ecology and the temperature-size rule Predicting population persistence and dynamics in the context of global change is a major challenge for ecology. Density of a population at carrying capacity is a key concept linking population dynamics to broader-scale patterns of biodiversity and population persistence. A widely held prediction is that population abundance at carrying capacity should decrease with warming. While it may seem counterintuitive that density should decrease when it’s warmer, the rationale is that as temperatures increase, individual metabolic rates are predicted to increase. If resource supply is limited and equal across all temperatures, then populations growing in warmer conditions should be able to support fewer individuals because each individual requires more metabolic resources to live. This prediction, which is based on the metabolic theory of ecology, has not been tested empirically. Here, using experimental populations of the green alga, Tetraselmis tetrahele, Joey Bernhardt, Jenn Sunday, and Mary O’Connor tested empirically whether effects of temperature on short-term metabolic performance (rates of photosynthesis and respiration) translate directly to effects of temperature on population dynamics. They measured per-capita metabolic rates and population abundances at carrying capacity across a temperature gradient spanning 5°C – 38°C. They found that carrying capacity declined with temperature, and that this decline in abundance was predicted by metabolic theory models. The temperature dependence of individual metabolic performance translated to population abundance. Concurrent with declines in abundance, they observed a linear decline in cell size of approximately 2% per degree Celsius, which is consistent with broadly observed patterns in unicellular organisms, known as the temperature-size rule. Their results indicate that outcomes of population dynamics across a range of temperatures reflect organismal responses to temperature via metabolic scaling, providing a general basis for forecasting population responses to global change.Abstract The temperature dependence of highly conserved subcellular metabolic systems affects ecological patterns and processes across scales, from organisms to ecosystems. Population density at carrying capacity plays an important role in evolutionary processes, biodiversity and ecosystem function, yet how it varies with temperature-dependent metabolism remains unclear. Though the exponential effect of temperature on intrinsic population growth rate, r, is well known, we still lack clear evidence that population density at carrying capacity, K, declines with increasing per-capita metabolic rate, as predicted by the metabolic theory of ecology (MTE). We experimentally tested whether temperature effects on photosynthesis propagate directly to population carrying capacity in a model species, the mobile phytoplankton Tetraselmis tetrahele. After maintaining populations at fixed resource supply and temperatures (6 levels) for 43 days, we found that carrying capacity declined with increasing temperature. This decline was predicted quantitatively when models included temperature-dependent metabolic rates and temperature-associated body size shifts. Our results demonstrate that warming reduces carrying capacity, and that temperature effects on body size and metabolic rate interact to determine how temperature affects population dynamics. These findings bolster efforts to relate metabolic temperature dependence to population and ecosystem patterns via MTE. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700114 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700114">Read the Article</a></i> </p> --> <p><b>Carrying capacity declines with warming, as predicted by the metabolic theory of ecology and the temperature-size rule </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>redicting population persistence and dynamics in the context of global change is a major challenge for ecology. Density of a population at carrying capacity is a key concept linking population dynamics to broader-scale patterns of biodiversity and population persistence. A widely held prediction is that population abundance at carrying capacity should decrease with warming. While it may seem counterintuitive that density should decrease when it’s warmer, the rationale is that as temperatures increase, individual metabolic rates are predicted to increase. If resource supply is limited and equal across all temperatures, then populations growing in warmer conditions should be able to support fewer individuals because each individual requires more metabolic resources to live. This prediction, which is based on the metabolic theory of ecology, has not been tested empirically. </p> <p>Here, using experimental populations of the green alga, <i>Tetraselmis tetrahele</i>, Joey Bernhardt, Jenn Sunday, and Mary O’Connor tested empirically whether effects of temperature on short-term metabolic performance (rates of photosynthesis and respiration) translate directly to effects of temperature on population dynamics. They measured per-capita metabolic rates and population abundances at carrying capacity across a temperature gradient spanning 5°C – 38°C. They found that carrying capacity declined with temperature, and that this decline in abundance was predicted by metabolic theory models. The temperature dependence of individual metabolic performance translated to population abundance. Concurrent with declines in abundance, they observed a linear decline in cell size of approximately 2% per degree Celsius, which is consistent with broadly observed patterns in unicellular organisms, known as the temperature-size rule. Their results indicate that outcomes of population dynamics across a range of temperatures reflect organismal responses to temperature via metabolic scaling, providing a general basis for forecasting population responses to global change.</p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he temperature dependence of highly conserved subcellular metabolic systems affects ecological patterns and processes across scales, from organisms to ecosystems. Population density at carrying capacity plays an important role in evolutionary processes, biodiversity and ecosystem function, yet how it varies with temperature-dependent metabolism remains unclear. Though the exponential effect of temperature on intrinsic population growth rate, <i>r</i>, is well known, we still lack clear evidence that population density at carrying capacity, <i>K</i>, declines with increasing per-capita metabolic rate, as predicted by the metabolic theory of ecology (MTE). We experimentally tested whether temperature effects on photosynthesis propagate directly to population carrying capacity in a model species, the mobile phytoplankton <i>Tetraselmis tetrahele</i>. After maintaining populations at fixed resource supply and temperatures (6 levels) for 43 days, we found that carrying capacity declined with increasing temperature. This decline was predicted quantitatively when models included temperature-dependent metabolic rates and temperature-associated body size shifts. Our results demonstrate that warming reduces carrying capacity, and that temperature effects on body size and metabolic rate interact to determine how temperature affects population dynamics. These findings bolster efforts to relate metabolic temperature dependence to population and ecosystem patterns via MTE. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Fri, 07 Sep 2018 05:00:00 GMT “‘Her joyous enthusiasm for her life-work…’ Early women authors in The American Naturalist” https://amnat.org/an/newpapers/DecBronstein.html The DOI will be https://dx.doi.org/10.1086/700119 Who were the early women authors in The&nbsp;American Naturalist? The natural sciences in the 19th century were almost exclusively studied by men. Almost. But a small number of remarkable, pioneering women overcame deeply entrenched cultural barriers to publish their own contributions to the natural sciences. This journal began publication in 1867, and for decades was the leading venue in America for publishing in the natural sciences, broadly defined. Although most American Naturalist articles were male-authored, women did contribute articles even in the journal’s first decades. Over 60 women contributed a total of nearly 80 articles during the journal’s first half-century. Here, Bronstein and Bolnick examine these womens’ scientific contributions to The&nbsp;American Naturalist, as well as their lives and the challenges they faced to enter and stay active in science. How were they drawn into science despite the barriers to entry for women? How did some manage to establish life-long careers in science? Abstract Women have long been underrepresented in the natural sciences, and although great progress has been made in recent decades, many subtle and not-so-subtle barriers persist. In this context, it is easy to get the impression that the early history of ecology and evolutionary biology was exclusively the domain of male researchers. In fact, a number of women made very substantial contributions to The&nbsp;American Naturalist in its first decades. As part of a series of retrospective essays celebrating 150 years of this journal, we highlight the scientific contributions of the women who published in it during its first fifty years (1867–1916). We also discuss the diverse paths that their scientific careers took, and the barriers that they faced along the way. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700119 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700119">Read the Article</a></i> </p> --><h2>Who were the early women authors in <i>The&nbsp;American Naturalist</i>?</h2> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he natural sciences in the 19th century were almost exclusively studied by men. Almost. But a small number of remarkable, pioneering women overcame deeply entrenched cultural barriers to publish their own contributions to the natural sciences. This journal began publication in 1867, and for decades was the leading venue in America for publishing in the natural sciences, broadly defined. Although most <i>American Naturalist</i> articles were male-authored, women did contribute articles even in the journal’s first decades. Over 60 women contributed a total of nearly 80 articles during the journal’s first half-century. Here, Bronstein and Bolnick examine these womens’ scientific contributions to <i>The&nbsp;American Naturalist</i>, as well as their lives and the challenges they faced to enter and stay active in science. How were they drawn into science despite the barriers to entry for women? How did some manage to establish life-long careers in science? </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>omen have long been underrepresented in the natural sciences, and although great progress has been made in recent decades, many subtle and not-so-subtle barriers persist. In this context, it is easy to get the impression that the early history of ecology and evolutionary biology was exclusively the domain of male researchers. In fact, a number of women made very substantial contributions to <i>The&nbsp;American Naturalist</i> in its first decades. As part of a series of retrospective essays celebrating 150 years of this journal, we highlight the scientific contributions of the women who published in it during its first fifty years (1867&ndash;1916). We also discuss the diverse paths that their scientific careers took, and the barriers that they faced along the way. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 28 Aug 2018 05:00:00 GMT “Purring crickets: The evolution of a novel sexual signal” https://amnat.org/an/newpapers/DecTinghitella.html The DOI will be https://dx.doi.org/10.1086/700116 Male crickets evolve novel ‘purring’ sound that attracts female mates. Are they crick-cats? Like us, many organisms communicate with one another using signals that can take the form of sounds, smells, colors, or behaviors. Communication between males and females of the same species is often required for reproduction, so when mating signals change dramatically there are important implications for speciation. Like any question about evolutionary change, when we study animal communication we usually do that by comparing species or other groups that have differed in signals for quite some time. But we cannot test definitively for a role of mating signals in creating and maintaining diversity unless we find a signal that has just evolved so that we can measure the signal and the receiver’s response to that signal at “time 0”, and then track the changes over time. Robin Tinghitella, Dale Broder, and colleagues recently discovered just such a situation when they visited the Kalaupapa National Historical Site on the Hawaiian island of Molokaʻi. Tinghitella has studied field crickets in Hawai‘i for 15 years and has been interested in the songs males produce by rubbing their wings together to attract females. Last May, just after dusk, she collected crickets on a lawn in Kalaupapa for the first time. She took them back to her room where she noticed a quiet purring sound. She instantly wondered whether she had a feline visitor. But the sound was coming from her box of crickets. In this unique place where there was no background anthropogenic noise, she was able to hear a totally novel cricket song for the first time! The Tinghitella lab group is calling the males who make this novel sound purring crickets—or crick-cats! Back in the lab, they began recording and characterizing the new song. It is much quieter, more broadband, and has a higher average peak frequency than a typical song from a male of this species. They also wondered if females could hear the new sound and use it to locate males. They played recordings to females from a speaker 1 meter away and found that about half of them could locate the speaker. This is such an exciting discovery—males are singing a brand new song and females can hear it and use it! In future work, the team will track this system over time to see whether and how the purring song coevolves with female receivers in real time—evolution in action! This one of very few discoveries of a novel sexual signal, and they will use it to better understand how new conversations begin and what they mean for boundaries between species. Abstract Opportunities to observe contemporary signal change are incredibly rare, but critical for understanding how diversity is created and maintained. We discovered a population of the Pacific field cricket (Teleogryllus oceanicus) with a newly evolved song (“purring”), different from any known cricket. Male crickets use song to attract females from afar and to court females once near. Teleogryllus oceanicus is well-known for sexual signal evolution, as exemplified by a recent signal loss. In this study, we characterized the new purring sound and investigated the role of the purr in long distance and short distance communication. The purring sound differed from typical ancestral calls in peak frequency, amplitude, and bandwidth. Further, the long-distance purring song facilitated mate location, though the role of courtship purring song is less clear. Our discovery of purring male crickets is an unprecedented opportunity to watch the emergence of a newly evolved sexual signal unfold in real time, and has potential to illuminate the mechanisms by which evolutionary novelties arise and coevolve between the sexes. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700116 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700116">Read the Article</a></i> </p> --> <p><b>Male crickets evolve novel ‘purring’ sound that attracts female mates. Are they crick-cats? </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">L</span>ike us, many organisms communicate with one another using signals that can take the form of sounds, smells, colors, or behaviors. Communication between males and females of the same species is often required for reproduction, so when mating signals change dramatically there are important implications for speciation. Like any question about evolutionary change, when we study animal communication we usually do that by comparing species or other groups that have differed in signals for quite some time. But we cannot test definitively for a role of mating signals in creating and maintaining diversity unless we find a signal that has <i>just</i> evolved so that we can measure the signal and the receiver’s response to that signal at “time 0”, and then track the changes over time. </p><p>Robin Tinghitella, Dale Broder, and colleagues recently discovered just such a situation when they visited the Kalaupapa National Historical Site on the Hawaiian island of Molokaʻi. Tinghitella has studied field crickets in Hawai‘i for 15 years and has been interested in the songs males produce by rubbing their wings together to attract females. Last May, just after dusk, she collected crickets on a lawn in Kalaupapa for the first time. She took them back to her room where she noticed a quiet purring sound. She instantly wondered whether she had a feline visitor. But the sound was coming from her box of crickets. In this unique place where there was no background anthropogenic noise, she was able to hear a totally novel cricket song for the first time! The Tinghitella lab group is calling the males who make this novel sound purring crickets—or crick-cats! Back in the lab, they began recording and characterizing the new song. It is much quieter, more broadband, and has a higher average peak frequency than a typical song from a male of this species. They also wondered if females could hear the new sound and use it to locate males. They played recordings to females from a speaker 1 meter away and found that about half of them could locate the speaker. This is such an exciting discovery—males are singing a brand new song and females can hear it and use it! In future work, the team will track this system over time to see whether and how the purring song coevolves with female receivers in real time—evolution in action! This one of very few discoveries of a novel sexual signal, and they will use it to better understand how new conversations begin and what they mean for boundaries between species. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">O</span>pportunities to observe contemporary signal change are incredibly rare, but critical for understanding how diversity is created and maintained. We discovered a population of the Pacific field cricket (<i>Teleogryllus oceanicus</i>) with a newly evolved song (“purring”), different from any known cricket. Male crickets use song to attract females from afar and to court females once near. <i>Teleogryllus oceanicus</i> is well-known for sexual signal evolution, as exemplified by a recent signal loss. In this study, we characterized the new purring sound and investigated the role of the purr in long distance and short distance communication. The purring sound differed from typical ancestral calls in peak frequency, amplitude, and bandwidth. Further, the long-distance purring song facilitated mate location, though the role of courtship purring song is less clear. Our discovery of purring male crickets is an unprecedented opportunity to watch the emergence of a newly evolved sexual signal unfold in real time, and has potential to illuminate the mechanisms by which evolutionary novelties arise and coevolve between the sexes. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 28 Aug 2018 05:00:00 GMT “Transgenerational and within-generation plasticity in response to climate change: insights from a manipulative field experiment across an elevational gradient” https://amnat.org/an/newpapers/DecWadgymar.html Read the Article Transgenerational and within-generation plasticity interact and vary clinally in populations across elevation gradients Environmental conditions strongly influence an individual’s phenotype and fitness. Temporal and spatial variation in the landscape can favor the evolution of phenotypic plasticity, such that one individual can produce different phenotypes depending on the environment it encounters. However, we know very little about the extent to which the environment a parent experiences affects the phenotypes of the offspring, and whether phenotypic plasticity across generations interacts with plasticity that arises within generations. Given the importance of environmental variation in the evolution of plasticity, populations distributed across gradients may have evolved different strategies for responding to changes in the environment. Studies of transgenerational and within-generation plasticity can reveal potential mechanisms through which populations or species could mitigate the effects of rapid climate change. Here, Wadgymar, MacTavish, and Anderson examine transgenerational and within-generation plasticity in life history traits in response to climate change in sixteen populations of the perennial forb, Boechera stricta (Drummond’s rockcress, in the Brassicaceae) distributed across an elevational gradient in the Rocky Mountains of Colorado. In the field, the researchers manipulated snowpack and the timing of snowmelt in a two-generation reciprocal transplant experiment conducted in three common gardens established near the lower, intermediate, and higher range boundaries of Boechera’s distribution in this region. In the greenhouse, they exposed plants to conditions simulating high and low elevation sites. In the field, the scientists discovered that transgenerational plasticity in seed mass, seed dormancy, and seedling emergence varied clinally across an elevational gradient and differed between snow-removal and control treatments. The arid and warm conditions typical of low-elevation sites and the researchers’ snow-removal treatment caused plants to produce smaller and more dormant seeds in comparison to the less-arid, cooler conditions typical of high-elevation sites and the control treatment. Small seeds had a greater probability of being non-viable, and low-elevation genotypes produce smaller seeds than high-elevation genotypes. Altogether, these results suggest that climate change may have disproportionately negative consequences for low-elevation populations, and that these effects are mediated, in part, by transgenerational plasticity. The results demonstrate that the effects of climate change on transgenerational plasticity are complex and context-dependent. The researchers propose that future studies should incorporate the influence of parental effects in studies of climate change, adaptation, and species persistence. Abstract Parental environmental effects, or transgenerational plasticity, can influence an individual’s phenotype or fitness, yet remain underexplored in the context of global change. Using the perennial self-pollinating plant Boechera stricta, we explored the effects of climate change on transgenerational and within-generation plasticity in dormancy, germination, growth, and survival. We first conducted a snow removal experiment in the field, in which we transplanted 16 families of known origin into three common gardens at different elevations and exposed half of the siblings to contemporary snow dynamics and half to early snow removal. We planted the offspring of these individuals in a factorial manipulation of temperature and water level in the growth chamber, and reciprocally transplanted them across all parental environments in the field. The growth chamber experiment revealed that the effects of transgenerational plasticity persist in traits expressed after establishment, even when accounting for parental effects on seed mass. The field experiment showed that transgenerational and within-generation plasticity can interact and that plasticity varies clinally in populations distributed across elevations. These findings demonstrate that transgenerational plasticity can influence fitness-related traits and should be incorporated in studies of biological responses to climate change. Plasticidad transgeneracional e intrageneracional en respuesta a los cambios climáticos: Resultados de un experimento de campo manipulativo a través de un gradiente de elevación Los efectos ambientales parentales, o la plasticidad transgeneracional, pueden influir en el fenotipo y la adecuación (fitness) de un individuo, pero permanecen poco estudiados en el contexto de los cambios climáticos. Utilizando la planta perenne y de autofecundación, Boechera stricta, exploramos los efectos del cambio climático sobre la plasticidad transgeneracional e intrageneracional en la dormancia, la germinación, el crecimiento y la supervivencia. Primero realizamos un experimento de remoción de la nieve en el campo, en el que trasplantamos 16 familias de origen conocido en tres jardines comunes a diferentes elevaciones. Expusimos la mitad de los individuos a las dinámicas contemporáneas de nieve y la otra mitad a la eliminación temprana de la nieve. Plantamos a los descendientes de estos individuos siguiendo una manipulación factorial de temperatura y nivel de agua en el laboratorio, y los trasplantamos recíprocamente a través de todos los ambientes paternales en el campo. El experimento controlado en el laboratorio reveló que los efectos de la plasticidad transgeneracional persisten en rasgos expresados después del establecimiento, incluso cuando se contabilizan los efectos paternos en el peso de la semilla. El experimento de campo mostró que la plasticidad transgeneracional e intrageneracional pueden interactuar y que la plasticidad varía de forma clinal en las poblaciones distribuidas a través de las elevaciones. Estos hallazgos demuestran que la plasticidad transgeneracional puede influir en los rasgos relacionados con la adecuación y debe ser incorporada en estudios de respuestas biológicas al cambio climático. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/700097"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700097">Read the Article</a></i> </p> --> <p><b>Transgenerational and within-generation plasticity interact and vary clinally in populations across elevation gradients </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">E</span>nvironmental conditions strongly influence an individual’s phenotype and fitness. Temporal and spatial variation in the landscape can favor the evolution of phenotypic plasticity, such that one individual can produce different phenotypes depending on the environment it encounters. However, we know very little about the extent to which the environment a parent experiences affects the phenotypes of the offspring, and whether phenotypic plasticity across generations interacts with plasticity that arises within generations. Given the importance of environmental variation in the evolution of plasticity, populations distributed across gradients may have evolved different strategies for responding to changes in the environment. Studies of transgenerational and within-generation plasticity can reveal potential mechanisms through which populations or species could mitigate the effects of rapid climate change. </p><p>Here, Wadgymar, MacTavish, and Anderson examine transgenerational and within-generation plasticity in life history traits in response to climate change in sixteen populations of the perennial forb, <i>Boechera stricta</i> (Drummond’s rockcress, in the Brassicaceae) distributed across an elevational gradient in the Rocky Mountains of Colorado. In the field, the researchers manipulated snowpack and the timing of snowmelt in a two-generation reciprocal transplant experiment conducted in three common gardens established near the lower, intermediate, and higher range boundaries of <i>Boechera</i>’s distribution in this region. In the greenhouse, they exposed plants to conditions simulating high and low elevation sites. </p><p>In the field, the scientists discovered that transgenerational plasticity in seed mass, seed dormancy, and seedling emergence varied clinally across an elevational gradient and differed between snow-removal and control treatments. The arid and warm conditions typical of low-elevation sites and the researchers’ snow-removal treatment caused plants to produce smaller and more dormant seeds in comparison to the less-arid, cooler conditions typical of high-elevation sites and the control treatment. Small seeds had a greater probability of being non-viable, and low-elevation genotypes produce smaller seeds than high-elevation genotypes. Altogether, these results suggest that climate change may have disproportionately negative consequences for low-elevation populations, and that these effects are mediated, in part, by transgenerational plasticity. The results demonstrate that the effects of climate change on transgenerational plasticity are complex and context-dependent. The researchers propose that future studies should incorporate the influence of parental effects in studies of climate change, adaptation, and species persistence. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">P</span>arental environmental effects, or transgenerational plasticity, can influence an individual’s phenotype or fitness, yet remain underexplored in the context of global change. Using the perennial self-pollinating plant <i>Boechera stricta</i>, we explored the effects of climate change on transgenerational and within-generation plasticity in dormancy, germination, growth, and survival. We first conducted a snow removal experiment in the field, in which we transplanted 16 families of known origin into three common gardens at different elevations and exposed half of the siblings to contemporary snow dynamics and half to early snow removal. We planted the offspring of these individuals in a factorial manipulation of temperature and water level in the growth chamber, and reciprocally transplanted them across all parental environments in the field. The growth chamber experiment revealed that the effects of transgenerational plasticity persist in traits expressed after establishment, even when accounting for parental effects on seed mass. The field experiment showed that transgenerational and within-generation plasticity can interact and that plasticity varies clinally in populations distributed across elevations. These findings demonstrate that transgenerational plasticity can influence fitness-related traits and should be incorporated in studies of biological responses to climate change. </p> <h4>Plasticidad transgeneracional e intrageneracional en respuesta a los cambios climáticos: Resultados de un experimento de campo manipulativo a través de un gradiente de elevación</h4> <p>Los efectos ambientales parentales, o la plasticidad transgeneracional, pueden influir en el fenotipo y la adecuación (fitness) de un individuo, pero permanecen poco estudiados en el contexto de los cambios climáticos. Utilizando la planta perenne y de autofecundación, <i>Boechera stricta</i>, exploramos los efectos del cambio climático sobre la plasticidad transgeneracional e intrageneracional en la dormancia, la germinación, el crecimiento y la supervivencia. Primero realizamos un experimento de remoción de la nieve en el campo, en el que trasplantamos 16 familias de origen conocido en tres jardines comunes a diferentes elevaciones. Expusimos la mitad de los individuos a las dinámicas contemporáneas de nieve y la otra mitad a la eliminación temprana de la nieve. Plantamos a los descendientes de estos individuos siguiendo una manipulación factorial de temperatura y nivel de agua en el laboratorio, y los trasplantamos recíprocamente a través de todos los ambientes paternales en el campo. El experimento controlado en el laboratorio reveló que los efectos de la plasticidad transgeneracional persisten en rasgos expresados después del establecimiento, incluso cuando se contabilizan los efectos paternos en el peso de la semilla. El experimento de campo mostró que la plasticidad transgeneracional e intrageneracional pueden interactuar y que la plasticidad varía de forma clinal en las poblaciones distribuidas a través de las elevaciones. Estos hallazgos demuestran que la plasticidad transgeneracional puede influir en los rasgos relacionados con la adecuación y debe ser incorporada en estudios de respuestas biológicas al cambio climático.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 21 Aug 2018 05:00:00 GMT “A comparative study of the role of sex-specific condition dependence in the evolution of sexually dimorphic traits” https://amnat.org/an/newpapers/DecRohner-A.html The DOI will be https://dx.doi.org/10.1086/700096 Abstract Sexual selection can displace traits acting as ornaments or armaments from their viability optimum in one sex, ultimately giving rise to sexual dimorphism. The degree of dimorphism should not only mirror the strength of sexual selection, but also the net viability costs and benefits of trait maintenance at equilibrium. As the ability of organisms to bear exaggerated traits will depend on their condition, more sexually dimorphic traits should also exhibit greater sex differences in condition dependence. While this has been demonstrated within species, similar patterns are expected across the phylogeny. We investigated this prediction within and across 11 (sub)species of sepsid flies with varying mating system. When estimating condition dependence for seven sexual and non-sexual traits that vary in their sexual dimorphism, we not only found a positive relationship between the sex difference in allometric slopes (our measure of condition dependence) and relative trait exaggeration within species, but also across species for those traits expected to be under sexual selection. Species with more pronounced male aggression had relatively larger and more condition-dependent male fore and mid legs. Our comparative study suggests a common genetic/developmental basis of sexual dimorphism and sex-specific plasticity that evolves across the phylogeny, and that the evolution of size consistently alters scaling relationships and thus contributes to the allometric variation of sexual armaments or ornaments in animals. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700096 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700096">Read the Article</a></i> </p> --><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>exual selection can displace traits acting as ornaments or armaments from their viability optimum in one sex, ultimately giving rise to sexual dimorphism. The degree of dimorphism should not only mirror the strength of sexual selection, but also the net viability costs and benefits of trait maintenance at equilibrium. As the ability of organisms to bear exaggerated traits will depend on their condition, more sexually dimorphic traits should also exhibit greater sex differences in condition dependence. While this has been demonstrated within species, similar patterns are expected across the phylogeny. We investigated this prediction within and across 11 (sub)species of sepsid flies with varying mating system. When estimating condition dependence for seven sexual and non-sexual traits that vary in their sexual dimorphism, we not only found a positive relationship between the sex difference in allometric slopes (our measure of condition dependence) and relative trait exaggeration within species, but also across species for those traits expected to be under sexual selection. Species with more pronounced male aggression had relatively larger and more condition-dependent male fore and mid legs. Our comparative study suggests a common genetic/developmental basis of sexual dimorphism and sex-specific plasticity that evolves across the phylogeny, and that the evolution of size consistently alters scaling relationships and thus contributes to the allometric variation of sexual armaments or ornaments in animals. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 16 Aug 2018 05:00:00 GMT “Genetic quality affects the rate of male and female reproductive ageing differently in Drosophila melanogaster” https://amnat.org/an/newpapers/DecBrengdahl.html The DOI will be https://dx.doi.org/10.1086/700117 Genetic quality affects the rate of male and female reproductive ageing differently in Drosophila melanogaster Why males and females of many species display different rates of ageing is puzzling and may hold the key to explain the enormous variation in ageing found among species. A team of researchers from Linköping University in Sweden has investigated the hypothesis that sex differences in reproductive ageing result from the sexes investing different amounts of their energy budgets into current reproduction and maintaining their bodies. To test this hypothesis, they varied the genetic quality of male and female fruit flies through the number of deleterious mutations they expressed, with consequences for how efficiently they could compete over food resources and convert these into usable energy. In response to the manipulation, the authors find that the pace of male reproductive ageing is unaltered by genetic quality, but that high-quality females show considerably slower reproductive ageing compared to low-quality females. These results suggest that high-quality females invest relatively more energy than low-quality females into maintaining their bodies and the opportunity to reproduce also later in life, while males, independently of their quality, focus on current reproduction. These results fit with the general view that males and females are selected to peruse different strategies to maximize reproductive success; as a consequence, males face fierce competition over access to females, and female production of eggs and offspring is primarily limited by access to resources. Abstract Males and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade-off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive ageing. Here we investigate if reproductive ageing and lifespan respond to condition differently in male and female Drosophila melanogaster, as predicted if sexual selection has shaped male and female resource allocation patterns. We manipulate condition through genetic quality, by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male than female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive ageing between the sexes in low condition, but in high condition reproductive ageing is relatively faster in males. No corresponding sex-specific change was found for lifespan. The sex difference in reproductive ageing appearing in high condition was due specifically to a decreased ageing rate in females, rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more towards somatic maintenance than males. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700117 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700117">Read the Article</a></i> </p> --> <p><b>Genetic quality affects the rate of male and female reproductive ageing differently in <i>Drosophila melanogaster</i> </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>hy males and females of many species display different rates of ageing is puzzling and may hold the key to explain the enormous variation in ageing found among species. A team of researchers from Linköping University in Sweden has investigated the hypothesis that sex differences in reproductive ageing result from the sexes investing different amounts of their energy budgets into current reproduction and maintaining their bodies. To test this hypothesis, they varied the genetic quality of male and female fruit flies through the number of deleterious mutations they expressed, with consequences for how efficiently they could compete over food resources and convert these into usable energy. In response to the manipulation, the authors find that the pace of male reproductive ageing is unaltered by genetic quality, but that high-quality females show considerably slower reproductive ageing compared to low-quality females. These results suggest that high-quality females invest relatively more energy than low-quality females into maintaining their bodies and the opportunity to reproduce also later in life, while males, independently of their quality, focus on current reproduction. These results fit with the general view that males and females are selected to peruse different strategies to maximize reproductive success; as a consequence, males face fierce competition over access to females, and female production of eggs and offspring is primarily limited by access to resources. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ales and females often maximize fitness by pursuing different reproductive strategies, with males commonly assumed to benefit more from increased resource allocation into current reproduction. Such investment should trade-off with somatic maintenance and may explain why males frequently live shorter than females. It also predicts that males should experience faster reproductive ageing. Here we investigate if reproductive ageing and lifespan respond to condition differently in male and female <i>Drosophila melanogaster</i>, as predicted if sexual selection has shaped male and female resource allocation patterns. We manipulate condition through genetic quality, by comparing individuals inbred or outbred for a major autosome. While genetic quality had a similar effect on condition in both sexes, condition had a much larger general effect on male than female reproductive output, as expected when sexual selection on vigor acts more strongly on males. We find no differences in reproductive ageing between the sexes in low condition, but in high condition reproductive ageing is relatively faster in males. No corresponding sex-specific change was found for lifespan. The sex difference in reproductive ageing appearing in high condition was due specifically to a decreased ageing rate in females, rather than any change in males. Our results suggest that females age slower than males in high condition primarily because sexual selection has favored sex differences in resource allocation under high condition, with females allocating relatively more towards somatic maintenance than males. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 16 Aug 2018 05:00:00 GMT “Natural selection on anti-helminth antibodies in a wild mammal population” https://amnat.org/an/newpapers/DecSparks.html The DOI will be https://dx.doi.org/10.1086/700115 Natural selection on immune responses vary across demographic groups but not environments in a wild mammal population The immune system is crucial in defending individuals against a multitude of parasites, and consequently effective immune responses are expected to be under selection. However, studies in the wild have shown there is considerable variation in immune responses between individuals. One explanation for the maintenance of such variability is that immune responses are energetically costly and this results in trade-offs with other traits such as growth and reproduction. The costs and benefits of immune responses may also vary by age and sex of the individual as well as their environment, but few studies have investigated this.Using data from a long-term individual-based study of wild Soay sheep living unmanaged in the St&nbsp;Kilda archipelago, the authors measured anti-parasite antibodies (IgA, IgE, IgG) in blood samples collected from sheep caught over a 25-year period. They then investigated whether these antibodies were associated with parasite fecal egg counts (a measure of parasite burden), weight, over-winter survival, and breeding success. Contrary to predictions, they did not find strong evidence for environment-dependent selection or costs associated with reproduction. The authors did find that high antibody levels predicted lower parasite egg counts and over-winter survival; however, this was dependent on the antibody isotype as well as the age and sex of the individual. Lambs with higher IgA levels had lower parasite egg counts but none of the antibodies were associated with over-winter survival. In contrast, adults with higher IgG levels had lower parasite egg counts and adult females with higher IgG levels were more likely to survive over winter. These results highlight the complexity of natural selection on immune traits in the wild and suggest that patterns of selection are unlikely to generalize across different immune measures or host demographic groups. Abstract An effective immune response is expected to confer fitness benefits through improved resistance to parasites but also incur energetic costs which negatively impact fitness-related traits such as reproduction. The fitness costs and benefits of an immune response are likely to depend on host age, sex, and levels of parasite exposure. Few studies have examined the full extent to which patterns of natural selection on immune phenotypes vary across demographic groups and environments in the wild. Here, we assessed natural selection on plasma levels of three functionally distinct isotypes (IgA, IgE and IgG) of antibodies against a prevalent nematode parasite measured in a wild Soay sheep population over 25 years. We found little support for environment-dependent selection or reproductive costs. However, antibody levels were negatively associated with parasite egg counts and positively associated with subsequent survival, albeit in a highly age- and isotype-dependent manner. Raised levels of anti-parasite IgA best predicted reduced egg counts but this did not predict survival in lambs. In adults increased anti-parasite IgG predicted reduced egg counts and in adult females IgG levels also positively predicted over-winter survival. Our results highlight the potential importance of age- and sex-dependent selection on immune phenotypes in nature, and show that patterns of selection can vary even amongst functionally-related immune markers. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700115 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700115">Read the Article</a></i> </p> --> <p><b>Natural selection on immune responses vary across demographic groups but not environments in a wild mammal population </b></p><p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">T</span>he immune system is crucial in defending individuals against a multitude of parasites, and consequently effective immune responses are expected to be under selection. However, studies in the wild have shown there is considerable variation in immune responses between individuals. One explanation for the maintenance of such variability is that immune responses are energetically costly and this results in trade-offs with other traits such as growth and reproduction. The costs and benefits of immune responses may also vary by age and sex of the individual as well as their environment, but few studies have investigated this.</p><p>Using data from a long-term individual-based study of wild Soay sheep living unmanaged in the St&nbsp;Kilda archipelago, the authors measured anti-parasite antibodies (IgA, IgE, IgG) in blood samples collected from sheep caught over a 25-year period. They then investigated whether these antibodies were associated with parasite fecal egg counts (a measure of parasite burden), weight, over-winter survival, and breeding success. Contrary to predictions, they did not find strong evidence for environment-dependent selection or costs associated with reproduction. The authors did find that high antibody levels predicted lower parasite egg counts and over-winter survival; however, this was dependent on the antibody isotype as well as the age and sex of the individual. Lambs with higher IgA levels had lower parasite egg counts but none of the antibodies were associated with over-winter survival. In contrast, adults with higher IgG levels had lower parasite egg counts and adult females with higher IgG levels were more likely to survive over winter. These results highlight the complexity of natural selection on immune traits in the wild and suggest that patterns of selection are unlikely to generalize across different immune measures or host demographic groups.</p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>n effective immune response is expected to confer fitness benefits through improved resistance to parasites but also incur energetic costs which negatively impact fitness-related traits such as reproduction. The fitness costs and benefits of an immune response are likely to depend on host age, sex, and levels of parasite exposure. Few studies have examined the full extent to which patterns of natural selection on immune phenotypes vary across demographic groups and environments in the wild. Here, we assessed natural selection on plasma levels of three functionally distinct isotypes (IgA, IgE and IgG) of antibodies against a prevalent nematode parasite measured in a wild Soay sheep population over 25 years. We found little support for environment-dependent selection or reproductive costs. However, antibody levels were negatively associated with parasite egg counts and positively associated with subsequent survival, albeit in a highly age- and isotype-dependent manner. Raised levels of anti-parasite IgA best predicted reduced egg counts but this did not predict survival in lambs. In adults increased anti-parasite IgG predicted reduced egg counts and in adult females IgG levels also positively predicted over-winter survival. Our results highlight the potential importance of age- and sex-dependent selection on immune phenotypes in nature, and show that patterns of selection can vary even amongst functionally-related immune markers. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 16 Aug 2018 05:00:00 GMT “Evolutionary responses to conditionality in species interactions across environmental gradients” https://amnat.org/an/newpapers/DecOBrien.html The DOI will be https://dx.doi.org/10.1086/700118 (Co)evolutionary outcomes of conditionality in biotic interactions: prediction, experiment design, and statistical test While we often characterize species interactions as being either beneficial or detrimental to the participants, in reality, the fitness outcomes of interactions can vary substantially, especially across environments (a.k.a. conditionality). A well-known example of such conditionality is the outcome of interactions between plants in the high alpine, where sites are cold, dry, and windy, and the substrate is unstable. Here, plants promote each others’ growth by buffering temperatures, wind, and soil erosion, but when the same species are neighbors lower on the same mountain slope, they compete with one another for resources. Ecological theory suggests that physical stress or the lack of availability of resources can determine the outcome of interactions: species interactions may become more positive (shift to mutually beneficial outcomes) under stressful conditions and become more negative when resources are freely available or when the physical environment is benign. Environmentally driven variation in interaction outcomes may also shape evolutionary responses of species. For example, selection may favor new mutations in interacting species that increase investment in beneficial interactions (mutualisms) at stressful ends of environmental gradients, leading to mutually beneficial coevolution between interacting partners. On the other hand, when stress is minimal or non-existent, one might predict no coevolution, or possibly antagonistic coevolution between interacting partners. Here, the authors develop and demonstrate new methods to empirically test these predictions. Insights gained from these models can be applied to a wide range of species interactions and conditional outcomes. Understanding these ecological and evolutionary forces will become increasingly important as species find themselves in novel interactions and physical contexts with climate change. Abstract The outcomes of many species interactions are conditional on the environments in which they occur. Often, interactions grade from being more positive under stressful or low-resource conditions to more antagonistic or neutral under benign conditions. Here, we take predictions of two well-supported ecological theories on conditionality—limiting resources models and the stress gradient hypothesis—and combine them with those from the geographic mosaic theory of coevolution (GMTC) to generate predictions for systematic patterns of adaptation and co-adaptation between partners along abiotic gradients. When interactions become more positive in stressful environments, mutations that increase fitness in one partner may also increase fitness in the other; because fitnesses are aligned, selection should favor greater mutualistic adaptation and co-adaptation between interacting species in stressful ends of environmental gradients. As a corollary, in benign environments, antagonistic co-adaptation could result in Red Queen or arms-race dynamics, or reduction of antagonism through character displacement and niche partitioning. Here, we distinguish between generally mutualistic or antagonistic adaptation (i.e., mutations in one partner that have similar effects across multiple populations of the other), versus specific adaptations to sympatric partners (local adaptation), which can occur either alone or simultaneously. We then outline the kinds of data required to test these predictions, develop experimental designs and statistical methods, and demonstrate these using simulations based on GMTC models. Our methods can be applied to a range of conditional outcomes, and may also be useful in assisted translocation approaches in the face of climate change. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700118 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700118">Read the Article</a></i> </p> --> <p><b>(Co)evolutionary outcomes of conditionality in biotic interactions: prediction, experiment design, and statistical test </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>hile we often characterize species interactions as being either beneficial or detrimental to the participants, in reality, the fitness outcomes of interactions can vary substantially, especially across environments (a.k.a. conditionality). A well-known example of such conditionality is the outcome of interactions between plants in the high alpine, where sites are cold, dry, and windy, and the substrate is unstable. Here, plants promote each others’ growth by buffering temperatures, wind, and soil erosion, but when the same species are neighbors lower on the same mountain slope, they compete with one another for resources. Ecological theory suggests that physical stress or the lack of availability of resources can determine the outcome of interactions: species interactions may become more positive (shift to mutually beneficial outcomes) under stressful conditions and become more negative when resources are freely available or when the physical environment is benign. </p> <p>Environmentally driven variation in interaction outcomes may also shape evolutionary responses of species. For example, selection may favor new mutations in interacting species that increase investment in beneficial interactions (mutualisms) at stressful ends of environmental gradients, leading to mutually beneficial coevolution between interacting partners. On the other hand, when stress is minimal or non-existent, one might predict no coevolution, or possibly antagonistic coevolution between interacting partners. </p> <p>Here, the authors develop and demonstrate new methods to empirically test these predictions. Insights gained from these models can be applied to a wide range of species interactions and conditional outcomes. Understanding these ecological and evolutionary forces will become increasingly important as species find themselves in novel interactions and physical contexts with climate change. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he outcomes of many species interactions are conditional on the environments in which they occur. Often, interactions grade from being more positive under stressful or low-resource conditions to more antagonistic or neutral under benign conditions. Here, we take predictions of two well-supported ecological theories on conditionality&mdash;limiting resources models and the stress gradient hypothesis&mdash;and combine them with those from the geographic mosaic theory of coevolution (GMTC) to generate predictions for systematic patterns of adaptation and co-adaptation between partners along abiotic gradients. When interactions become more positive in stressful environments, mutations that increase fitness in one partner may also increase fitness in the other; because fitnesses are aligned, selection should favor greater mutualistic adaptation and co-adaptation between interacting species in stressful ends of environmental gradients. As a corollary, in benign environments, antagonistic co-adaptation could result in Red Queen or arms-race dynamics, or reduction of antagonism through character displacement and niche partitioning. Here, we distinguish between generally mutualistic or antagonistic adaptation (i.e., mutations in one partner that have similar effects across multiple populations of the other), versus specific adaptations to sympatric partners (local adaptation), which can occur either alone or simultaneously. We then outline the kinds of data required to test these predictions, develop experimental designs and statistical methods, and demonstrate these using simulations based on GMTC models. Our methods can be applied to a range of conditional outcomes, and may also be useful in assisted translocation approaches in the face of climate change. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 14 Aug 2018 05:00:00 GMT “Eco-evolutionary dynamics in metacommunities: ecological inheritance, helping within- and harming between-species” https://amnat.org/an/newpapers/DecMullon-A.html The DOI will be https://dx.doi.org/10.1086/700094 Abstract Understanding selection on intra- and inter-specific interactions that take place in dispersal-limited communities is a challenge for ecology and evolutionary biology. The problem is that local demographic stochasticity generates eco-evolutionary dynamics that are generally too complicated to make tractable analytical investigations. Here, we circumvent this problem by approximating the selection gradient on a quantitative trait that influences local community dynamics, assuming that such dynamics are deterministic with a stable fixed point. We nonetheless incorporate unavoidable kin selection effects arising from demographic stochasticity. Our approximation reveals that selection depends on how an individual expressing a trait-change influences: (1) its own fitness and the fitness of its current relatives; and (2) the fitness of its downstream relatives through modifications of local ecological conditions (i.e., through ecological inheritance). Mathematically, the effects of ecological inheritance on selection are captured by dispersal-limited versions of press-perturbations of community ecology. We use our approximation to investigate the evolution of helping within- and harming between-species when these behaviours influence demography. We find that altruistic helping evolves more readily when intra-specific competition is for material resources rather than for space because in this case, the costs of kin competition tend to paid by downstream relatives. Similarly, altruistic harming between species evolves when it alleviates downstream relatives from inter-specific competition. Beyond these examples, our approximation can help better understand the influence of ecological inheritance on a variety of eco-evolutionary dynamics in metacommunities, from consumer-resource and predator-prey coevolution to selection on mating systems with demographic feedbacks. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700094 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700094">Read the Article</a></i> </p> --><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">U</span>nderstanding selection on intra- and inter-specific interactions that take place in dispersal-limited communities is a challenge for ecology and evolutionary biology. The problem is that local demographic stochasticity generates eco-evolutionary dynamics that are generally too complicated to make tractable analytical investigations. Here, we circumvent this problem by approximating the selection gradient on a quantitative trait that influences local community dynamics, assuming that such dynamics are deterministic with a stable fixed point. We nonetheless incorporate unavoidable kin selection effects arising from demographic stochasticity. Our approximation reveals that selection depends on how an individual expressing a trait-change influences: (1) its own fitness and the fitness of its current relatives; and (2) the fitness of its downstream relatives through modifications of local ecological conditions (i.e., through ecological inheritance). Mathematically, the effects of ecological inheritance on selection are captured by dispersal-limited versions of press-perturbations of community ecology. We use our approximation to investigate the evolution of helping within- and harming between-species when these behaviours influence demography. We find that altruistic helping evolves more readily when intra-specific competition is for material resources rather than for space because in this case, the costs of kin competition tend to paid by downstream relatives. Similarly, altruistic harming between species evolves when it alleviates downstream relatives from inter-specific competition. Beyond these examples, our approximation can help better understand the influence of ecological inheritance on a variety of eco-evolutionary dynamics in metacommunities, from consumer-resource and predator-prey coevolution to selection on mating systems with demographic feedbacks. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 14 Aug 2018 05:00:00 GMT “The cost of being big: local competition, importance of dispersal, and experimental evolution of reversal to unicellularity” https://amnat.org/an/newpapers/DecRebolleda.html The DOI will be https://dx.doi.org/10.1086/700095 Multicellularity (staying-together) did not evolve on land: why? Potentially high competition and dispersal constraints Multicellularity has evolved independently multiple times, and in many cases, unicellularity has evolved again from multicellular ancestors. Cancers, for example, are evolutionary reversals to unicellularity, in which cells no longer act as part of a larger coordinated whole, but as autonomous entities. Research in multicellularity has focused on these challenges of cooperation. However, cooperation and conflict are not the only challenges faced by multicellular organisms. The appearance of multicellular life is one of the biggest increases in size in the fossil record, and being big comes with challenges of its own. In this study María Rebolleda-Gómez and Michael Travisano evaluated the costs of multicellularity in recently evolved multicellular phenotypes that evolved in the laboratory as a result of selection for increased size. Combining growth assays, competition experiments, computer simulations, and experimental evolution, they show that costs of resource acquisition and local competition can readily lead to the evolution of reversals to single cells. These costs depend on the size of the multicellular organisms, their ability to disperse and the distribution of resources. In liquid media—where resources are evenly distributed—multicellularity imposes spatial structure and internal cells have less space and/or fewer resources for growth. In contrast, on plates, despite similar growth between multicellular and unicellular isolates (because single cells cannot move away from each other during growth), multicellular isolates are rapidly outcompeted by their unicellular ancestor. In this environment, every time a subset of the population is established in a new plate, unicellular isolates can disperse better and are able to take advantage of more resources. Multicellular individuals are comprised of multiple cells that all compete for the same resources. As a result, selection on plates but not on liquid leads to rapid reversals to unicellularity. Multicellularity has evolved independently more than 20 times with very different consequences in each of these transitions. A better understanding of the physical and ecological consequences of the morphological changes during the evolution of multicellularity can help us understand this multicellular diversity. Local competition and dispersal limitations may be among the reasons why most multicellular forms that develop through cells staying together have evolved in water, whereas most of the land origins of multicellularity involve single cells coming together temporarily (and often as a means for dispersal). Multicellularity transformed the physical space in which cells interact and this paper provides insight into the physical, ecological, and evolutionary limitations of this major transition. Abstract Multicellularity provides multiple benefits. Nonetheless, unicellularity is ubiquitous and there have been multiple cases of evolutionary reversal to a unicellular organization. In this paper, we explore some of the costs of multicellularity as well as the possibility and dynamics of evolutionary reversals to unicellularity. We hypothesize that recently evolved multicellular organisms would face a high cost of increased competition for local resources in spatially structured environments because of larger size and increased cell densities. To test this hypothesis we conducted competition assays, computer simulations, and selection experiments using isolates of Saccharomyces cerevisiae that recently evolved multicellularity. In well-mixed environments, multicellular isolates had lower growth rates relative to their unicellular ancestor due to limitations of space and resource acquisition. In structured environments with localized resources, cells in both multicellular and unicellular isolates grew at a similar rate. Despite similar growth, higher local density of cells in multicellular groups led to increased competition and higher fitness costs in spatially structured environments. In structured environments all of the multicellular isolates rapidly evolved a predominantly unicellular life cycle, while in well-mixed environments reversal was more gradual. Taken together, these results suggest that a lack of dispersal, leading to higher local competition, might have been one of the main constraints in the evolution of early multicellular forms. El costo de ser grande: competencia local, importancia de dispersión y evolución experimental de reversiones a unicelularidad Aunque la multicelularidad provee diversos beneficios, la vida unicelular es ubicua y ha habido varios casos de reversiones evolutivas a una forma de organización unicelular. En este artículo exploramos algunos de los costos de la multicelularidad, así como la posibilidad y las dinámicas de reversión a la unicelularidad. Nuestra hipótesis es que, en ambientes con estructura espacial, organismos que evolucionaron multicellularidad recientemente, van a enfrentar mayores costos asociados con una mayor competencia por los recursos locales, debido a que los organismos multicelulares tienen un mayor tamaño y mayores densidades celulares. Para evaluar esta hipótesis, realizamos ensayos de competencia, simulaciones de computadora y evolución experimental con aislados de Saccharomyces cerevisiae que recientemente evolucionaron fenotípos multicelulares. En ambientes con agitación constante, los aislados multicellulares tienen menores tasas de crecimiento que su ancestro unicelular debido a limitaciones de espacio y adqusición de recursos. En ambientes espacialmente estructurados, con recursos localizados, las células de aislados unicelulares y multicelulares crecen a la misma velocidad. Sin embargo, la mayor densidad local de células en grupos multicelulares resultó en mayor competencia y costos de adecuación en ambientes con estructura espacial. En estos ambientes con recursos localizados todos los aislados multicelulares evolucionaron un ciclo de vida principalmente unicelular, mientras que en ambientes con una distribución más homogénea la reversión a unicelularidad fue mucho más gradual. Juntos, estos resultados sugieren que la falta de dispersión, que resulta en una mayor competencia, puede haber sido una de las principales restricciones en la evolución de las primeras formas multicelulares. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/700095 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/700095">Read the Article</a></i> </p> --> <p><b>Multicellularity (staying-together) did not evolve on land: why? Potentially high competition and dispersal constraints </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ulticellularity has evolved independently multiple times, and in many cases, unicellularity has evolved again from multicellular ancestors. Cancers, for example, are evolutionary reversals to unicellularity, in which cells no longer act as part of a larger coordinated whole, but as autonomous entities. Research in multicellularity has focused on these challenges of cooperation. However, cooperation and conflict are not the only challenges faced by multicellular organisms. The appearance of multicellular life is one of the biggest increases in size in the fossil record, and being big comes with challenges of its own. </p><p>In this study María Rebolleda-Gómez and Michael Travisano evaluated the costs of multicellularity in recently evolved multicellular phenotypes that evolved in the laboratory as a result of selection for increased size. Combining growth assays, competition experiments, computer simulations, and experimental evolution, they show that costs of resource acquisition and local competition can readily lead to the evolution of reversals to single cells. These costs depend on the size of the multicellular organisms, their ability to disperse and the distribution of resources. In liquid media—where resources are evenly distributed—multicellularity imposes spatial structure and internal cells have less space and/or fewer resources for growth. In contrast, on plates, despite similar growth between multicellular and unicellular isolates (because single cells cannot move away from each other during growth), multicellular isolates are rapidly outcompeted by their unicellular ancestor. In this environment, every time a subset of the population is established in a new plate, unicellular isolates can disperse better and are able to take advantage of more resources. Multicellular individuals are comprised of multiple cells that all compete for the same resources. As a result, selection on plates but not on liquid leads to rapid reversals to unicellularity. </p><p>Multicellularity has evolved independently more than 20 times with very different consequences in each of these transitions. A better understanding of the physical and ecological consequences of the morphological changes during the evolution of multicellularity can help us understand this multicellular diversity. Local competition and dispersal limitations may be among the reasons why most multicellular forms that develop through cells staying together have evolved in water, whereas most of the land origins of multicellularity involve single cells coming together temporarily (and often as a means for dispersal). Multicellularity transformed the physical space in which cells interact and this paper provides insight into the physical, ecological, and evolutionary limitations of this major transition. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ulticellularity provides multiple benefits. Nonetheless, unicellularity is ubiquitous and there have been multiple cases of evolutionary reversal to a unicellular organization. In this paper, we explore some of the costs of multicellularity as well as the possibility and dynamics of evolutionary reversals to unicellularity. We hypothesize that recently evolved multicellular organisms would face a high cost of increased competition for local resources in spatially structured environments because of larger size and increased cell densities. To test this hypothesis we conducted competition assays, computer simulations, and selection experiments using isolates of <i>Saccharomyces cerevisiae</i> that recently evolved multicellularity. In well-mixed environments, multicellular isolates had lower growth rates relative to their unicellular ancestor due to limitations of space and resource acquisition. In structured environments with localized resources, cells in both multicellular and unicellular isolates grew at a similar rate. Despite similar growth, higher local density of cells in multicellular groups led to increased competition and higher fitness costs in spatially structured environments. In structured environments all of the multicellular isolates rapidly evolved a predominantly unicellular life cycle, while in well-mixed environments reversal was more gradual. Taken together, these results suggest that a lack of dispersal, leading to higher local competition, might have been one of the main constraints in the evolution of early multicellular forms. </p> <h4>El costo de ser grande: competencia local, importancia de dispersión y evolución experimental de reversiones a unicelularidad</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>unque la multicelularidad provee diversos beneficios, la vida unicelular es ubicua y ha habido varios casos de reversiones evolutivas a una forma de organización unicelular. En este artículo exploramos algunos de los costos de la multicelularidad, así como la posibilidad y las dinámicas de reversión a la unicelularidad. Nuestra hipótesis es que, en ambientes con estructura espacial, organismos que evolucionaron multicellularidad recientemente, van a enfrentar mayores costos asociados con una mayor competencia por los recursos locales, debido a que los organismos multicelulares tienen un mayor tamaño y mayores densidades celulares. Para evaluar esta hipótesis, realizamos ensayos de competencia, simulaciones de computadora y evolución experimental con aislados de <i>Saccharomyces cerevisiae</i> que recientemente evolucionaron fenotípos multicelulares. En ambientes con agitación constante, los aislados multicellulares tienen menores tasas de crecimiento que su ancestro unicelular debido a limitaciones de espacio y adqusición de recursos. En ambientes espacialmente estructurados, con recursos localizados, las células de aislados unicelulares y multicelulares crecen a la misma velocidad. Sin embargo, la mayor densidad local de células en grupos multicelulares resultó en mayor competencia y costos de adecuación en ambientes con estructura espacial. En estos ambientes con recursos localizados todos los aislados multicelulares evolucionaron un ciclo de vida principalmente unicelular, mientras que en ambientes con una distribución más homogénea la reversión a unicelularidad fue mucho más gradual. Juntos, estos resultados sugieren que la falta de dispersión, que resulta en una mayor competencia, puede haber sido una de las principales restricciones en la evolución de las primeras formas multicelulares. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 14 Aug 2018 05:00:00 GMT “Considerations used by desert isopods to assess scorpion predation risk” https://amnat.org/an/newpapers/NovZaguri.html Read the Article Assessing the risk assessment – which predatory cues and in what context will justify an anti-predatory response? “The world is a dangerous place to live,” wrote Albert Einstein. This is most likely what desert isopods think every morning when leaving the safety of their family burrows to forage in a landscape full of threats. Trying to reveal how prey distinguish between safe and dangerous areas is a major experimental challenge because it requires inferring sensory abilities and cognitive decisions from their behavioral reactions. In this paper, Zaguri, Zohar, and Hawlena from the Ecostress lab at the Hebrew University of Jerusalem have explored how isopods assess the threat of golden Israeli scorpion predation in the central Negev desert. They introduced different combinations of signals that scorpions leave behind to the isopod natural habitat, and meticulously measured the isopods’ behavioral responses to these signals upon first encountering them. Isopods can identify the smell of a scorpion but respond to them only when this smell is associated with other odors or excavated soil mounds that imply an active scorpion burrow. This risk assessment process is efficient because golden scorpions hunt isopods only from the depth of the burrow. Simultaneous presence of different predator cues provoked graded defense reaction, possibly reflecting an additive increase in risk estimation. Our results suggest that isopods can modify their risk estimation based on the context in which the cue is perceived. Abstract Animals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use complex risk assessment process that estimates risks and weigh costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (Hemilepistus reaumuri) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions upon first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated-soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow, or when they lack data to refute this possibility. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699840"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699840">Read the Article</a></i> </p> --> <p><b>Assessing the risk assessment &ndash; which predatory cues and in what context will justify an anti-predatory response? </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">“T</span>he world is a dangerous place to live,” wrote Albert Einstein. This is most likely what desert isopods think every morning when leaving the safety of their family burrows to forage in a landscape full of threats. Trying to reveal how prey distinguish between safe and dangerous areas is a major experimental challenge because it requires inferring sensory abilities and cognitive decisions from their behavioral reactions. In this paper, Zaguri, Zohar, and Hawlena from the Ecostress lab at the Hebrew University of Jerusalem have explored how isopods assess the threat of golden Israeli scorpion predation in the central Negev desert. They introduced different combinations of signals that scorpions leave behind to the isopod natural habitat, and meticulously measured the isopods’ behavioral responses to these signals upon first encountering them. Isopods can identify the smell of a scorpion but respond to them only when this smell is associated with other odors or excavated soil mounds that imply an active scorpion burrow. This risk assessment process is efficient because golden scorpions hunt isopods only from the depth of the burrow. Simultaneous presence of different predator cues provoked graded defense reaction, possibly reflecting an additive increase in risk estimation. Our results suggest that isopods can modify their risk estimation based on the context in which the cue is perceived. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>nimals adjust behaviors to balance changes in predation risk against other vital needs. Animals must therefore collect sensory information and use complex risk assessment process that estimates risks and weigh costs and benefits entailed in different reactions. Studying this cognitive process is challenging, especially in nature because it requires inferring sensory abilities and conscious decisions from behavioral reactions. Our goal was to address this empirical challenge by implementing psychophysical principles to field research that explores considerations used by desert isopods (<i>Hemilepistus reaumuri</i>) to assess the risk of scorpions that hunt exclusively from within their burrows. We introduced various combinations of chemical and physical cues to the vicinity of isopod burrows and recorded their detailed reactions upon first encountering the cues. The isopods reacted defensively to scorpion odor but only when accompanied with excavated-soil or other odors typically found near scorpion burrows. Isopods also reacted defensively to piles of excavated soil without scorpion olfactory cues, suggesting that isopods take precautions even against physical disturbances that do not necessarily reflect predator activity. Simultaneous presence of different cues provoked graded responses, possibly reflecting an additive increase in risk estimation. We conclude that wild isopods use defensive reactions toward environmental signals only when the integrated perceptual information implies an active scorpion burrow, or when they lack data to refute this possibility. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 01 Aug 2018 05:00:00 GMT “Atypical flowers can be as profitable as typical hummingbird flowers” https://amnat.org/an/newpapers/NovWaser.html Read the Article Don’t ignore the unexpected! Our example: visits to “atypical” flowers can be surprisingly profitable for hummingbirds What is a hummingbird flower? It may not be what you expect! Nick Waser and Mary Price began to learn this lesson while camping as graduate students in the 1970s. They were repeatedly surprised to see hummingbirds systematically visiting flowers that lacked the characteristic features of “typical” hummingbird flowers. Curious about whether the birds were being “duped” by these flowers, they began to measure foraging rates of the birds and the energy content of nectar provided by a variety of atypical and typical flowers and to compare that with what was known about the birds’ energetic needs. They continued their observations opportunistically over the next four decades at various locations throughout the southwestern USA, eventually enlisting help from younger colleague Paul CaraDonna. The three ecologists discovered that the birds are making no mistake in their behavior—the atypical flowers often are just as energetically profitable as typical red, tubular hummingbird flowers. In fact, the nectar rewards of atypical flowers in some cases appear to be adequate by themselves to support the high metabolic needs of hummingbirds throughout a 24-hour period. What these observations tell us is that atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly scarce in suitable resources. They also emphasize what can be gained by attending to the unexpected. Abstract In western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of “hummingbird flowers”. Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbirds. Our field measurements of nectar content and hummingbird foraging speeds, taken over four decades at multiple localities, show that atypical flowers can be as profitable as typical ones and suggest that the profit can support 24-hr metabolic requirements of the birds. Thus, atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly depauperate in suitable resources. These results illustrate what can be gained by attending to the unexpected. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699836"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699836">Read the Article</a></i> </p> --> <p><b>Don&rsquo;t ignore the unexpected! Our example: visits to &ldquo;atypical&rdquo; flowers can be surprisingly profitable for hummingbirds </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>hat is a hummingbird flower? It may not be what you expect! Nick Waser and Mary Price began to learn this lesson while camping as graduate students in the 1970s. They were repeatedly surprised to see hummingbirds systematically visiting flowers that lacked the characteristic features of “typical” hummingbird flowers. Curious about whether the birds were being “duped” by these flowers, they began to measure foraging rates of the birds and the energy content of nectar provided by a variety of atypical and typical flowers and to compare that with what was known about the birds’ energetic needs. They continued their observations opportunistically over the next four decades at various locations throughout the southwestern USA, eventually enlisting help from younger colleague Paul CaraDonna. The three ecologists discovered that the birds are making no mistake in their behavior—the atypical flowers often are just as energetically profitable as typical red, tubular hummingbird flowers. In fact, the nectar rewards of atypical flowers in some cases appear to be adequate by themselves to support the high metabolic needs of hummingbirds throughout a 24-hour period. What these observations tell us is that atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly scarce in suitable resources. They also emphasize what can be gained by attending to the unexpected. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n western North America, hummingbirds can be observed systematically visiting flowers that lack the typical reddish color, tubular morphology, and dilute nectar of “hummingbird flowers”. Curious about this behavior, we asked whether these atypical flowers are energetically profitable for hummingbirds. Our field measurements of nectar content and hummingbird foraging speeds, taken over four decades at multiple localities, show that atypical flowers can be as profitable as typical ones and suggest that the profit can support 24-hr metabolic requirements of the birds. Thus, atypical flowers may contribute to successful migration of hummingbirds, enhance their population densities, and allow them to occupy areas seemingly depauperate in suitable resources. These results illustrate what can be gained by attending to the unexpected. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 25 Jul 2018 05:00:00 GMT “Periodic, parasite-mediated selection for and against sex” https://amnat.org/an/newpapers/NovGibson.html Read the Article Coevolving parasites drive fluctuations in the fitness of asexual reproduction: a long-term field and experimental study Sexual reproduction isn’t an efficient way to make offspring, because males do not give birth. To make the most grandchildren, an individual female should, theoretically, clone herself. Why then is sexual reproduction such a common reproductive strategy? The Red Queen hypothesis suggests that parasites periodically give sexual females an advantage over clonal females. This study supports the Red Queen hypothesis: long-term field and experimental data indicate that parasites drive fluctuations in the fitness and frequency of clones. These long-term field data revealed dramatic variation in the infection rate of asexual females at Lake Alexandrina: in the early 2000s, asexual females were substantially more infected by a sterilizing trematode (Microphallus) than were sexual females. By 2012, asexual females had declined in frequency and become substantially less infected than sexual females. In contrast to the wide variation in asexual infection, the infection rate of sexual females remained steady over the years.The researchers predicted that these rare asexual females should begin to increase in frequency, because (1) asexuals can make more grand-offspring than sexuals and (2) they were less infected than the sexuals. If asexual females did not increase in frequency, the authors would reject the Red Queen hypothesis, because some force other than parasites must be preventing asexuals from outcompeting sexuals. In support of the prediction, asexual females nearly tripled in frequency at Lake Alexandrina from 2012 to 2016. The researchers ran a parallel experiment in freshwater tanks, where they allowed sexual and asexual snails from Lake Alexandrina to compete with one another in a simplified environment that isolated the effect of parasites. Asexual females also increased in frequency in these tanks. The fact that the researchers saw similar results in the field and the tanks argues that parasites contributed to the changes in asexual frequency in the field. These results show periodic selection both for and against sex. The study demonstrates the need for long-term field data in studying host-parasite coevolution and the Red Queen. Single snapshots in time would present a misleading, simplified picture of parasite-mediated selection on reproductive mode. In keeping with this lesson, the researchers continue to follow the ongoings at Lake Alexandrina – they predict that the local parasites will begin to heavily infect asexuals again as asexual females increase in frequency. Abstract Asexual lineages should rapidly replace sexual populations. Why sex then? The Red Queen hypothesis proposes that parasite-mediated selection against common host genotypes could counteract the per-capita birth rate advantage of asexuals. Under the Red Queen, fluctuations in parasite-mediated selection can drive fluctuations in the asexual population, leading to the coexistence of sexual and asexual reproduction. Does shifting selection by parasites drive fluctuations in the fitness and frequency of asexuals in nature? Combining long-term field data with mesocosm experiments, we detected a shift in the direction of parasite selection in the snail Potamopyrgus antipodarum and its coevolving parasite Microphallus sp. In the early 2000s, asexuals were more infected than sexuals. A decade later, the asexuals had declined in frequency and were less infected than sexuals. Over time, the mean infection prevalence of asexuals equaled that of sexuals, but varied far more. This variation in asexual infection prevalence suggests the potential for parasite-mediated fluctuations in asexual fitness. Accordingly, we detected fitness consequences of the shift in parasite selection: when they were less infected than sexuals, asexuals increased in frequency in the field and in paired mesocosms that isolated the effect of parasites. The match between field and experiment argues that coevolving parasites drive temporal change in the relative fitness and frequency of asexuals, potentially promoting the coexistence of reproductive modes in P.&nbsp;antipodarum. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699829"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699829">Read the Article</a></i> </p> --> <p><b>Coevolving parasites drive fluctuations in the fitness of asexual reproduction: a long-term field and experimental study </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>exual reproduction isn’t an efficient way to make offspring, because males do not give birth. To make the most grandchildren, an individual female should, theoretically, clone herself. Why then is sexual reproduction such a common reproductive strategy? The Red Queen hypothesis suggests that parasites periodically give sexual females an advantage over clonal females. This study supports the Red Queen hypothesis: long-term field and experimental data indicate that parasites drive fluctuations in the fitness and frequency of clones. </p><p>These long-term field data revealed dramatic variation in the infection rate of asexual females at Lake Alexandrina: in the early 2000s, asexual females were substantially more infected by a sterilizing trematode (<I>Microphallus</I>) than were sexual females. By 2012, asexual females had declined in frequency and become substantially less infected than sexual females. In contrast to the wide variation in asexual infection, the infection rate of sexual females remained steady over the years.</p><p>The researchers predicted that these rare asexual females should begin to increase in frequency, because (1) asexuals can make more grand-offspring than sexuals and (2) they were less infected than the sexuals. If asexual females did not increase in frequency, the authors would reject the Red Queen hypothesis, because some force other than parasites must be preventing asexuals from outcompeting sexuals. In support of the prediction, asexual females nearly tripled in frequency at Lake Alexandrina from 2012 to 2016. The researchers ran a parallel experiment in freshwater tanks, where they allowed sexual and asexual snails from Lake Alexandrina to compete with one another in a simplified environment that isolated the effect of parasites. Asexual females also increased in frequency in these tanks. The fact that the researchers saw similar results in the field and the tanks argues that parasites contributed to the changes in asexual frequency in the field. </p><p>These results show periodic selection both for and against sex. The study demonstrates the need for long-term field data in studying host-parasite coevolution and the Red Queen. Single snapshots in time would present a misleading, simplified picture of parasite-mediated selection on reproductive mode. In keeping with this lesson, the researchers continue to follow the ongoings at Lake Alexandrina – they predict that the local parasites will begin to heavily infect asexuals again as asexual females increase in frequency. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>sexual lineages should rapidly replace sexual populations. Why sex then? The Red Queen hypothesis proposes that parasite-mediated selection against common host genotypes could counteract the per-capita birth rate advantage of asexuals. Under the Red Queen, fluctuations in parasite-mediated selection can drive fluctuations in the asexual population, leading to the coexistence of sexual and asexual reproduction. Does shifting selection by parasites drive fluctuations in the fitness and frequency of asexuals in nature? Combining long-term field data with mesocosm experiments, we detected a shift in the direction of parasite selection in the snail <i>Potamopyrgus antipodarum</i> and its coevolving parasite <i>Microphallus</i> sp. In the early 2000s, asexuals were more infected than sexuals. A decade later, the asexuals had declined in frequency and were less infected than sexuals. Over time, the mean infection prevalence of asexuals equaled that of sexuals, but varied far more. This variation in asexual infection prevalence suggests the potential for parasite-mediated fluctuations in asexual fitness. Accordingly, we detected fitness consequences of the shift in parasite selection: when they were less infected than sexuals, asexuals increased in frequency in the field and in paired mesocosms that isolated the effect of parasites. The match between field and experiment argues that coevolving parasites drive temporal change in the relative fitness and frequency of asexuals, potentially promoting the coexistence of reproductive modes in <i>P.&nbsp;antipodarum</i>. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 25 Jul 2018 05:00:00 GMT “The biogeographical patterns of species richness and abundance distribution in stream diatoms are driven by climate and water chemistry” https://amnat.org/an/newpapers/NovPassy.html The DOI will be https://dx.doi.org/10.1086/699830 Stream diatom richness and abundance distribution at subcontinental scales are driven by climate and water chemistry The declines in biodiversity at higher latitudes and elevations are among the oldest studied, yet still not fully explained ecological patterns. Related to biodiversity is the balance between common and rare species, reflected in the shape of the species abundance distribution (SAD). Higher biodiversity is linked to greater community functionality and improved services to humans, such as increased water quality. The degree of species commonness and rarity has implications for ecosystem functions and conservation. While there are many, predominantly climate-based theories and hypotheses about the spatial variability in biodiversity, little is known about the patterns and causes of variability in the SAD. To address this deficiency, an international team of scientists, led by Dr. Sophia Passy from the University of Texas at Arlington, has explored the biodiversity and SAD of diatoms, an important group of producers in stream ecosystems. They demonstrated that in both the US and Finland, diatom richness and the SAD exhibited distinct spatial patterns (i.e., primarily longitudinal in the US, but latitudinal in Finland), deviating from prior observations and thus inconsistent with existing climate-based concepts. These patterns were instead described with climate-water chemistry models, showing that more diverse communities with a more even distribution of common and rare species occur in streams of higher temperature seasonality and total phosphorus levels. Given that temperature seasonality is projected to decrease with global warming because the cold months are becoming warmer, diatom biodiversity and abundance equality may decline and lead to diminished community services. The operation of both climate and water chemistry mechanisms in structuring diatom communities underscores their complex response to the environment and the necessity for novel predictive frameworks. Abstract In this inter-continental study of stream diatoms, we asked three important but still unresolved ecological questions: 1) What factors drive the biogeography of species richness and species abundance distribution (SAD); 2) Are climate-related hypotheses, which have dominated the research on the latitudinal and altitudinal diversity gradients, adequate in explaining spatial biotic variability; and 3) Is the SAD response to the environment independent of richness? We tested a number of climatic theories and hypotheses (i.e., the species-energy theory, the metabolic theory, the energy variability hypothesis, and the climatic tolerance hypothesis) but found no support for any of these concepts as the relationships of richness with explanatory variables were non-existent, weak or unexpected. Instead, we demonstrated that diatom richness and SAD evenness generally increased with temperature seasonality and at mid- to high total phosphorus concentrations. The spatial patterns of diatom richness and the SAD—mainly longitudinal in the US, but latitudinal in Finland—were defined primarily by the covariance of climate and water chemistry with space. The SAD was not entirely controlled by richness, emphasizing its utility for ecological research. Thus, we found support for the operation of both climate and water chemistry mechanisms in structuring diatom communities, which underscores their complex response to the environment and the necessity for novel predictive frameworks. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699830 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699830">Read the Article</a></i> </p> --> <p><b>Stream diatom richness and abundance distribution at subcontinental scales are driven by climate and water chemistry </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he declines in biodiversity at higher latitudes and elevations are among the oldest studied, yet still not fully explained ecological patterns. Related to biodiversity is the balance between common and rare species, reflected in the shape of the species abundance distribution (SAD). Higher biodiversity is linked to greater community functionality and improved services to humans, such as increased water quality. The degree of species commonness and rarity has implications for ecosystem functions and conservation. While there are many, predominantly climate-based theories and hypotheses about the spatial variability in biodiversity, little is known about the patterns and causes of variability in the SAD. To address this deficiency, an international team of scientists, led by Dr. Sophia Passy from the University of Texas at Arlington, has explored the biodiversity and SAD of diatoms, an important group of producers in stream ecosystems. They demonstrated that in both the US and Finland, diatom richness and the SAD exhibited distinct spatial patterns (i.e., primarily longitudinal in the US, but latitudinal in Finland), deviating from prior observations and thus inconsistent with existing climate-based concepts. These patterns were instead described with climate-water chemistry models, showing that more diverse communities with a more even distribution of common and rare species occur in streams of higher temperature seasonality and total phosphorus levels. Given that temperature seasonality is projected to decrease with global warming because the cold months are becoming warmer, diatom biodiversity and abundance equality may decline and lead to diminished community services. The operation of both climate and water chemistry mechanisms in structuring diatom communities underscores their complex response to the environment and the necessity for novel predictive frameworks. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n this inter-continental study of stream diatoms, we asked three important but still unresolved ecological questions: 1) What factors drive the biogeography of species richness and species abundance distribution (SAD); 2) Are climate-related hypotheses, which have dominated the research on the latitudinal and altitudinal diversity gradients, adequate in explaining spatial biotic variability; and 3) Is the SAD response to the environment independent of richness? We tested a number of climatic theories and hypotheses (i.e., the species-energy theory, the metabolic theory, the energy variability hypothesis, and the climatic tolerance hypothesis) but found no support for any of these concepts as the relationships of richness with explanatory variables were non-existent, weak or unexpected. Instead, we demonstrated that diatom richness and SAD evenness generally increased with temperature seasonality and at mid- to high total phosphorus concentrations. The spatial patterns of diatom richness and the SAD—mainly longitudinal in the US, but latitudinal in Finland—were defined primarily by the covariance of climate and water chemistry with space. The SAD was not entirely controlled by richness, emphasizing its utility for ecological research. Thus, we found support for the operation of both climate and water chemistry mechanisms in structuring diatom communities, which underscores their complex response to the environment and the necessity for novel predictive frameworks. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 25 Jul 2018 05:00:00 GMT “Multi-scale immune selection and the transmission-diversity feedback in antigenically diverse pathogen systems” https://amnat.org/an/newpapers/DecHolding-A.html Read the Article Mathematical model shows how immune selection balances the transmission-diversity feedback in pathogen systems Abstract Antigenic diversity is commonly used by pathogens to enhance their transmission success. Within-host clonal antigenic variation helps to maintain long infectious periods, whereas high levels of allelic diversity at the population-level significantly expands the pool of susceptible individuals. Diversity, however, is not necessarily a static property of a pathogen population but in many cases generated by the very act of infection and transmission, and it is therefore expected to respond dynamically to changes in transmission and immune selection. We hypothesised that this coupling creates a positive feedback whereby infection and disease transmission promote the generation of diversity, which itself facilitates immune evasion and further infections. To investigate this link in more detail we considered the human malaria parasite Plasmodium falciparum, one of the most important antigenically diverse pathogens. We developed an individual-based model in which antigenic diversity emerges as a dynamic property from the underlying transmission processes. Our results show that the balance between stochastic extinction and the generation of new antigenic variants is intrinsically linked to within-host and between-host immune selection. This in turn determines the level of diversity that can be maintained in a given population. Furthermore, the transmission-diversity feedback can lead to temporal lags in the response to natural or intervention-induced perturbations in transmission rates. Our results therefore have important implications for monitoring and assessing the effectiveness of disease control efforts. More forthcoming papers &raquo; <p><strong><a href="https://dx.doi.org/10.1086/699535"><i>Read the Article</i></a></strong></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699535">Read the Article</a></i> </p> --> <p><b>Mathematical model shows how immune selection balances the transmission-diversity feedback in pathogen systems </b></p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>ntigenic diversity is commonly used by pathogens to enhance their transmission success. Within-host clonal antigenic variation helps to maintain long infectious periods, whereas high levels of allelic diversity at the population-level significantly expands the pool of susceptible individuals. Diversity, however, is not necessarily a static property of a pathogen population but in many cases generated by the very act of infection and transmission, and it is therefore expected to respond dynamically to changes in transmission and immune selection. We hypothesised that this coupling creates a positive feedback whereby infection and disease transmission promote the generation of diversity, which itself facilitates immune evasion and further infections. To investigate this link in more detail we considered the human malaria parasite <i>Plasmodium falciparum</i>, one of the most important antigenically diverse pathogens. We developed an individual-based model in which antigenic diversity emerges as a dynamic property from the underlying transmission processes. Our results show that the balance between stochastic extinction and the generation of new antigenic variants is intrinsically linked to within-host and between-host immune selection. This in turn determines the level of diversity that can be maintained in a given population. Furthermore, the transmission-diversity feedback can lead to temporal lags in the response to natural or intervention-induced perturbations in transmission rates. Our results therefore have important implications for monitoring and assessing the effectiveness of disease control efforts. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 25 Jul 2018 05:00:00 GMT “Early and adult social environments shape sex-specific actuarial senescence patterns in a cooperative breeder” https://amnat.org/an/newpapers/OctVBerger.html Read the Article Individuals from social species typically show a slow growth, a delayed age at first reproduction, and a long life compared to individuals from non-social species with similar size. In cooperative breeders such as meerkats, wolves, or beavers, helpers assist a dominant pair to raise pups. So far, whether sociality influences actuarial senescence (i.e. the age-specific decrease in survival) remains unknown, although helpers take care of pups, which contributes to decreasing the amount of energy that dominants allocate to parental care. We can thus expect that the presence of helpers delays and slows down senescence. A team of researchers from the University of Lyon combined their expertise in demography and sociality to test this expectation in a cooperative breeder, the Alpine marmot. They found that the beneficial effect of helpers depended on the timing of the help. Having helpers as adult slowed down much senescence more than having helpers early in life. Moreover, the benefits of being helped was sex-specific, with actuarial senescence reduced in females but not in males. Their work emphasizes that sociality influences senescence but that the benefits in terms of reduced senescence are sex-specific and depend on when help occurs. These findings have important theoretical implications on current evolutionary theories of ageing, which do not include yet a social component. Abstract Sociality modulates life history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided, and on the sex of the dominant. Being helped when adult slowed down senescence in both sexes. However, the effect of the presence of helpers during the year of birth of a dominant was sex-specific. Among dominants helped during adulthood, females born in the presence of helpers senesced slower, whereas males senesced faster. Among dominants without helpers during adulthood, females with helpers at birth senesced faster. Social environment modulates senescence, but acts differently between sexes and life stages. Résumé : Les environnements sociaux précoce et adulte déterminent les patrons de sénescence actuarielle spécifiques aux sexes chez une espèce à reproduction coopérative La socialité détermine les traits d’histoire de vie par des modifications de l’allocation des ressources aux traits liés à la valeur sélective. Cependant, l’influence des facteurs sociaux à différentes étapes du cycle de vie sur la sénescence reste encore largement méconnue. Afin de répondre à cette question, nous avons mesuré l’influence de l’environnement social précoce et adulte sur la sénescence actuarielle chez la marmotte alpine, une espèce pratiquant l’élevage coopératif. L’influence d’auxiliaires sur la sénescence actuarielle diffère très fortement selon le moment du cycle de vie où l’aide est apportée et selon le sexe du dominant. Recevoir de l’aide durant la vie adulte ralentit la sénescence dans les deux sexes. Cependant, l’effet de la présence d’auxiliaires à la naissance du dominant diffère entre sexes. Parmi les dominants qui ont reçu de l’aide durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus lentement alors que les mâles vieillissent plus vite. Parmi les dominants qui n’ont pas bénéficié d’auxiliaires durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus vite. L’environnement social détermine donc la sénescence, mais les effets diffèrent selon le sexe et les étapes de vie. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699513"><i>Read the Article </i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699513">Read the Article</a></i> </p> --><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>ndividuals from social species typically show a slow growth, a delayed age at first reproduction, and a long life compared to individuals from non-social species with similar size. In cooperative breeders such as meerkats, wolves, or beavers, helpers assist a dominant pair to raise pups. So far, whether sociality influences actuarial senescence (i.e. the age-specific decrease in survival) remains unknown, although helpers take care of pups, which contributes to decreasing the amount of energy that dominants allocate to parental care. We can thus expect that the presence of helpers delays and slows down senescence.</p> <p>A team of researchers from the University of Lyon combined their expertise in demography and sociality to test this expectation in a cooperative breeder, the Alpine marmot. They found that the beneficial effect of helpers depended on the timing of the help. Having helpers as adult slowed down much senescence more than having helpers early in life. Moreover, the benefits of being helped was sex-specific, with actuarial senescence reduced in females but not in males.</p> <p>Their work emphasizes that sociality influences senescence but that the benefits in terms of reduced senescence are sex-specific and depend on when help occurs. These findings have important theoretical implications on current evolutionary theories of ageing, which do not include yet a social component. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>ociality modulates life history traits through changes in resource allocation to fitness-related traits. However, how social factors at different stages of the life cycle modulate senescence remains poorly understood. To address this question, we assessed the influence of social environment in both early life and adulthood on actuarial senescence in the Alpine marmot, a cooperative breeder. The influence of helpers on actuarial senescence strongly differed depending on when help was provided, and on the sex of the dominant. Being helped when adult slowed down senescence in both sexes. However, the effect of the presence of helpers during the year of birth of a dominant was sex-specific. Among dominants helped during adulthood, females born in the presence of helpers senesced slower, whereas males senesced faster. Among dominants without helpers during adulthood, females with helpers at birth senesced faster. Social environment modulates senescence, but acts differently between sexes and life stages. </p> <h4>Résumé : Les environnements sociaux précoce et adulte déterminent les patrons de sénescence actuarielle spécifiques aux sexes chez une espèce à reproduction coopérative</h4> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">L</span>a socialité détermine les traits d’histoire de vie par des modifications de l’allocation des ressources aux traits liés à la valeur sélective. Cependant, l’influence des facteurs sociaux à différentes étapes du cycle de vie sur la sénescence reste encore largement méconnue. Afin de répondre à cette question, nous avons mesuré l’influence de l’environnement social précoce et adulte sur la sénescence actuarielle chez la marmotte alpine, une espèce pratiquant l’élevage coopératif. L’influence d’auxiliaires sur la sénescence actuarielle diffère très fortement selon le moment du cycle de vie où l’aide est apportée et selon le sexe du dominant. Recevoir de l’aide durant la vie adulte ralentit la sénescence dans les deux sexes. Cependant, l’effet de la présence d’auxiliaires à la naissance du dominant diffère entre sexes. Parmi les dominants qui ont reçu de l’aide durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus lentement alors que les mâles vieillissent plus vite. Parmi les dominants qui n’ont pas bénéficié d’auxiliaires durant leur vie adulte, les femelles nées avec des auxiliaires vieillissent plus vite. L’environnement social détermine donc la sénescence, mais les effets diffèrent selon le sexe et les étapes de vie. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Wed, 25 Jul 2018 05:00:00 GMT “A new framework for evaluating estimates of symbiotic nitrogen fixation in forests” https://amnat.org/an/newpapers/NovWinbourne-A.html Read the Article Rates of symbiotic nitrogen fixation are more uncertain than previously believed, shown with field data and simulations Abstract Symbiotic nitrogen fixation (SNF) makes atmospheric nitrogen biologically available and regulates carbon storage in many terrestrial ecosystems. Despite its global importance, estimates of SNF rates are highly uncertain, particularly in tropical forests where rates are assumed to be high. Here we provide a framework for evaluating the uncertainty of sample-based SNF estimates and discuss its implications for quantifying SNF and thus understanding of forest function. We apply this framework to field datasets from six lowland tropical rainforests (mature and secondary) in Brazil and Costa Rica. We use this dataset to estimate parameters influencing SNF estimation error, notably the root nodule abundance and variation in SNF rates among soil cores containing root nodules. We then use simulations to gauge the relationship between sampling effort and SNF estimation accuracy for a combination of parameters. Field data illuminate a highly right skewed log-normal distribution of SNF rates among soil cores containing root nodules which were rare and spanned five orders of magnitude. Consequently, simulations demonstrated that sample sizes of hundreds to even thousands of soil cores are needed to obtain estimates of SNF that are within, for example, a factor of 2 of the actual rate with 75% probability. This represents sample sizes that are larger than most studies to date. As a result of this previously undescribed uncertainty, we suggest current estimates of SNF in tropical forests are not sufficiently constrained to elucidate forest stand-level controls of SNF, which hinders our understanding of the impact of SNF on tropical forest ecosystem processes. Uma nova abordagem para avaliar as estimativas de fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio em florestas A&nbsp;fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio (FSN) torna o nitrog&ecirc;nio atmosf&eacute;rico biologicamente dispon&iacute;vel e regula o armazenamento de carbono em muitos ecossistemas terrestres. Apesar da sua import&acirc;ncia global, as estimativas de taxas de FSN ainda s&atilde;o muito incertas, principalmente em florestas tropicais, onde presume-se que as taxas sejam altas. O presente estudo avalia as incertezas nas estimativas de FSN baseadas em coleta de amostras e discute as implica&ccedil;&otilde;es desses resultados na quantifica&ccedil;&atilde;o de FSN, com intuito de melhorar o entendimento sobre o funcionamento das florestas tropicais. Esse esquema de avalia&ccedil;&atilde;o de incerteza foi aplicado a um conjunto de dados oriundos de seis florestas tropicais de terras baixas (maduras e secund&aacute;rias) localizadas no Brasil e na Costa Rica. Usamos esse conjunto de dados para estimar os par&acirc;metros que influenciam o erro da estimativa de FSN, principalmente a abund&acirc;ncia de n&oacute;dulos radiculares e varia&ccedil;&atilde;o nas taxas de FSN. Em seguida, calculamos atrav&eacute;s de simula&ccedil;&otilde;es a rela&ccedil;&atilde;o entre o esfor&ccedil;o de amostragem e a precis&atilde;o da estimativa de FSN. Os dados de campo evidenciam uma distribui&ccedil;&atilde;o log-normal com alta assimetria &agrave; direita das taxas de FSN nas amostras de solo contendo n&oacute;dulos de raiz, os quais foram raros. Consequentemente, as simula&ccedil;&otilde;es demonstraram que s&atilde;o necess&aacute;rias centenas ou at&eacute; mesmo milhares de amostras para se obter estimativas de FSN que tenham, por exemplo, 75% de probabilidade de distar da taxa verdadeira 2 vezes ou menos. Esse n&uacute;mero &eacute; muito maior do que o usado na maioria dos estudos j&aacute; publicados. Sugerimos que estimativas atuais de FSN em florestas tropicais s&atilde;o muito incertas para elucidar os controles de FSN em n&iacute;vel de parcelas amostrais, dificultando nossa compreens&atilde;o do impacto da FSN nos processos ecossist&ecirc;micos das florestas tropicais. More forthcoming papers &raquo; <p><a href="https://dx.doi.org/10.1086/699828"><i>Read the Article</i></a></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699828">Read the Article</a></i> </p> --> <p><b>Rates of symbiotic nitrogen fixation are more uncertain than previously believed, shown with field data and simulations </b></p><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">S</span>ymbiotic nitrogen fixation (SNF) makes atmospheric nitrogen biologically available and regulates carbon storage in many terrestrial ecosystems. Despite its global importance, estimates of SNF rates are highly uncertain, particularly in tropical forests where rates are assumed to be high. Here we provide a framework for evaluating the uncertainty of sample-based SNF estimates and discuss its implications for quantifying SNF and thus understanding of forest function. We apply this framework to field datasets from six lowland tropical rainforests (mature and secondary) in Brazil and Costa Rica. We use this dataset to estimate parameters influencing SNF estimation error, notably the root nodule abundance and variation in SNF rates among soil cores containing root nodules. We then use simulations to gauge the relationship between sampling effort and SNF estimation accuracy for a combination of parameters. Field data illuminate a highly right skewed log-normal distribution of SNF rates among soil cores containing root nodules which were rare and spanned five orders of magnitude. Consequently, simulations demonstrated that sample sizes of hundreds to even thousands of soil cores are needed to obtain estimates of SNF that are within, for example, a factor of 2 of the actual rate with 75% probability. This represents sample sizes that are larger than most studies to date. As a result of this previously undescribed uncertainty, we suggest current estimates of SNF in tropical forests are not sufficiently constrained to elucidate forest stand-level controls of SNF, which hinders our understanding of the impact of SNF on tropical forest ecosystem processes.</p> <h4>Uma nova abordagem para avaliar as estimativas de fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio em florestas</h4> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">A</span>&nbsp;fixa&ccedil;&atilde;o simbi&oacute;tica de nitrog&ecirc;nio (FSN) torna o nitrog&ecirc;nio atmosf&eacute;rico biologicamente dispon&iacute;vel e regula o armazenamento de carbono em muitos ecossistemas terrestres. Apesar da sua import&acirc;ncia global, as estimativas de taxas de FSN ainda s&atilde;o muito incertas, principalmente em florestas tropicais, onde presume-se que as taxas sejam altas. O presente estudo avalia as incertezas nas estimativas de FSN baseadas em coleta de amostras e discute as implica&ccedil;&otilde;es desses resultados na quantifica&ccedil;&atilde;o de FSN, com intuito de melhorar o entendimento sobre o funcionamento das florestas tropicais. Esse esquema de avalia&ccedil;&atilde;o de incerteza foi aplicado a um conjunto de dados oriundos de seis florestas tropicais de terras baixas (maduras e secund&aacute;rias) localizadas no Brasil e na Costa Rica. Usamos esse conjunto de dados para estimar os par&acirc;metros que influenciam o erro da estimativa de FSN, principalmente a abund&acirc;ncia de n&oacute;dulos radiculares e varia&ccedil;&atilde;o nas taxas de FSN. Em seguida, calculamos atrav&eacute;s de simula&ccedil;&otilde;es a rela&ccedil;&atilde;o entre o esfor&ccedil;o de amostragem e a precis&atilde;o da estimativa de FSN. Os dados de campo evidenciam uma distribui&ccedil;&atilde;o log-normal com alta assimetria &agrave; direita das taxas de FSN nas amostras de solo contendo n&oacute;dulos de raiz, os quais foram raros. Consequentemente, as simula&ccedil;&otilde;es demonstraram que s&atilde;o necess&aacute;rias centenas ou at&eacute; mesmo milhares de amostras para se obter estimativas de FSN que tenham, por exemplo, 75% de probabilidade de distar da taxa verdadeira 2 vezes ou menos. Esse n&uacute;mero &eacute; muito maior do que o usado na maioria dos estudos j&aacute; publicados. Sugerimos que estimativas atuais de FSN em florestas tropicais s&atilde;o muito incertas para elucidar os controles de FSN em n&iacute;vel de parcelas amostrais, dificultando nossa compreens&atilde;o do impacto da FSN nos processos ecossist&ecirc;micos das florestas tropicais.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"><span style="font-family: Georgia; font-size: large;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 24 Jul 2018 05:00:00 GMT “Early-life stress strengthens trait covariance: a plastic response that results in reduced flexibility” https://amnat.org/an/newpapers/NovMerrill.html The DOI will be https://dx.doi.org/10.1086/699839 Early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications Nobody likes stress; it can result in suppressed immunity, increased levels of free radicals, and elevated energy expenditure, among others. But for most organisms, once the stressor has passed, things revert to normal. For developing organisms, however, stressful experiences can have permanent effects. Individuals stressed in early life may be smaller, have less impressive sexual displays, develop altered stress responses later in life, and have modified immune function. In addition to impacting the development of these individual traits, early-life stress could also alter the relationships among different traits, or within traits over time by more broadly impacting an organism’s developmental machinery. Merrill and Grindstaff investigated this idea and found that zebra finches exposed to simulated early-life stress in the form of daily oral doses of the “stress hormone” corticosterone, developed along more rigid trajectories.As metrics of developmental flexibility, Merrill and Grindstaff measured morphological and physiological traits in control and corticosterone-treated birds prior to, during, and after corticosterone administration, which occurred during the nestling and fledgling stages. They then examined the strength of association within traits over time (e.g. body mass when the birds were 10 and 60 days old) and among different traits at the same age (e.g. body mass and wing length when the birds were 60 days old) to determine whether early-life stress resulted in tighter or weaker trait correlations. All of the within-trait correlations, and the vast majority of the among-trait correlations, were tighter for corticosterone-treated birds, providing strong evidence that sustained exposure to elevated levels of this stress hormone in early-life broadly alters developmental patterns. This is important because independent of early-life treatment, birds with tighter within and among trait correlations died earlier. If developmental flexibility is constrained by early-life stress, then this alteration may have profound impacts on the organism and could limit capacity to respond to changing environmental conditions. Abstract Stress exposure during development can impact both the expression of individual traits and associations between traits, but whether stress results in stronger or weaker associations between traits is unclear. In this study, we examined within and among-trait associations for morphological and physiological traits in zebra finches (Taeniopygia guttata) exposed to corticosterone (CORT) during the nestling and fledgling stages, and in control birds. Birds exposed to CORT exhibited stronger within-trait correlations over time and stronger associations among traits. We found preliminary evidence that birds that died before the median age of death had stronger within and among-trait correlations independent of treatment, and among CORT-treated birds, smaller birds were more likely to survive beyond the median age than larger birds. These findings suggest that early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications, and that these costs may be greater for larger offspring. Furthermore, our results provide experimental evidence for pleiotropic effects of hormones during development through altered patterns of phenotypic correlation. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699839 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699839">Read the Article</a></i> </p> --> <p><b>Early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">N</span>obody likes stress; it can result in suppressed immunity, increased levels of free radicals, and elevated energy expenditure, among others. But for most organisms, once the stressor has passed, things revert to normal. For developing organisms, however, stressful experiences can have permanent effects. Individuals stressed in early life may be smaller, have less impressive sexual displays, develop altered stress responses later in life, and have modified immune function. In addition to impacting the development of these individual traits, early-life stress could also alter the relationships among different traits, or within traits over time by more broadly impacting an organism’s developmental machinery. Merrill and Grindstaff investigated this idea and found that zebra finches exposed to simulated early-life stress in the form of daily oral doses of the “stress hormone” corticosterone, developed along more rigid trajectories.</p><p>As metrics of developmental flexibility, Merrill and Grindstaff measured morphological and physiological traits in control and corticosterone-treated birds prior to, during, and after corticosterone administration, which occurred during the nestling and fledgling stages. They then examined the strength of association within traits over time (e.g. body mass when the birds were 10 and 60 days old) and among different traits at the same age (e.g. body mass and wing length when the birds were 60 days old) to determine whether early-life stress resulted in tighter or weaker trait correlations. All of the within-trait correlations, and the vast majority of the among-trait correlations, were tighter for corticosterone-treated birds, providing strong evidence that sustained exposure to elevated levels of this stress hormone in early-life broadly alters developmental patterns. This is important because independent of early-life treatment, birds with tighter within and among trait correlations died earlier. If developmental flexibility is constrained by early-life stress, then this alteration may have profound impacts on the organism and could limit capacity to respond to changing environmental conditions. </p><hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">S</span>tress exposure during development can impact both the expression of individual traits and associations between traits, but whether stress results in stronger or weaker associations between traits is unclear. In this study, we examined within and among-trait associations for morphological and physiological traits in zebra finches (<i>Taeniopygia guttata</i>) exposed to corticosterone (CORT) during the nestling and fledgling stages, and in control birds. Birds exposed to CORT exhibited stronger within-trait correlations over time and stronger associations among traits. We found preliminary evidence that birds that died before the median age of death had stronger within and among-trait correlations independent of treatment, and among CORT-treated birds, smaller birds were more likely to survive beyond the median age than larger birds. These findings suggest that early-life stress hormone exposure can result in reduced developmental flexibility, with potential fitness ramifications, and that these costs may be greater for larger offspring. Furthermore, our results provide experimental evidence for pleiotropic effects of hormones during development through altered patterns of phenotypic correlation. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 24 Jul 2018 05:00:00 GMT “Female-biased sex ratios increase colony survival and reproductive output in the spider Anelosimus studiosus” https://amnat.org/an/newpapers/NovLichtenstein.html The DOI will be https://dx.doi.org/10.1086/699838 Female-biased sex ratios increase social spider colony survival, generating group selection on female-biased sex ratios Animals across the world tend to have 1&thinsp;:&thinsp;1 sex ratios, because whichever sex is rarer, it will always be advantageous to produce more of it. However, a few animals have highly female-skewed ratios, including social spiders, inbred spiders that work together to capture prey. In a new paper appearing in The&nbsp;American Naturalist, James L. L. Lichtenstein and colleagues evaluate one advantage to producing many daughters: Extremely inbred social groups with many females can grow more quickly, helping groups survive and reproduce. The authors tested this by assembling colonies of the semi-social spider Anelosimus studiosus and then putting colonies in the wild with manipulated sizes and sex ratios in areas where spider colonies thrive and places where they struggle. The researchers thought that groups with female-biased sex ratios would be more likely to survive and produce egg cases, especially for small colonies and colonies in areas where spiders struggle to survive. After five months, the scientists returned to these colonies to see whether they were alive and how many egg cases they produced. As expected, female-biased colonies were more likely to survive and produced more egg cases. These advantages were stronger when spider colonies were small and were in tough areas. This means that colonies full of female spiders were able to flourish in harrowing conditions by doing more helping capture prey and maintain webs more than male spiders, producing offspring who can work, or both. This advantage may explain the evolution of female-biased ratios in this very interesting yet very specific case. Abstract Negative frequency-dependent selection acting on the sexes is hypothesized to drive populations towards a balanced sex ratio. However, numerous examples of female-biased sex ratios pepper the arthropods. Theoretical examinations have proposed that female-biased populations or groups can have higher chances of surviving and propagating, which may be advantageous. We evaluate this hypothesis in the semi-social spider, Anelosimus studiosus, by creating artificial colonies of varying sex ratios and sizes and observing colony performance at sites with high vs. low group extinction rates. We also tested whether colony extinction rates and sex ratios were correlated across 25 collection sites spanning 10º latitude. We found that colonies with female-biased sex ratios produced more egg cases and were more likely to survive the duration of a field season, suggesting that female-biased sex ratios confer both survival and reproductive advantages upon colonies. The effect of sex ratio on colony survival and reproductive output was strongest for small colonies in high extinction areas. Moreover, we found that female-biased sex ratios correlated with greater extinction rates across 25 sites, indicating that female-biased sex ratios may have evolved at some sites in response to high extinction rates. These findings suggest that selection favoring groups with female-biased sex ratios may operate in A.&nbsp;studiosus, shedding light on some of factors that may drive the evolution of biased sex ratios. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699838 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699838">Read the Article</a></i> </p> --> <p><b>Female-biased sex ratios increase social spider colony survival, generating group selection on female-biased sex ratios </b></p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>nimals across the world tend to have 1&thinsp;:&thinsp;1 sex ratios, because whichever sex is rarer, it will always be advantageous to produce more of it. However, a few animals have highly female-skewed ratios, including social spiders, inbred spiders that work together to capture prey. In a new paper appearing in <i>The&nbsp;American Naturalist</i>, James L. L. Lichtenstein and colleagues evaluate one advantage to producing many daughters: Extremely inbred social groups with many females can grow more quickly, helping groups survive and reproduce. The authors tested this by assembling colonies of the semi-social spider <i>Anelosimus studiosus</i> and then putting colonies in the wild with manipulated sizes and sex ratios in areas where spider colonies thrive and places where they struggle. The researchers thought that groups with female-biased sex ratios would be more likely to survive and produce egg cases, especially for small colonies and colonies in areas where spiders struggle to survive. After five months, the scientists returned to these colonies to see whether they were alive and how many egg cases they produced. </p> <p>As expected, female-biased colonies were more likely to survive and produced more egg cases. These advantages were stronger when spider colonies were small and were in tough areas. This means that colonies full of female spiders were able to flourish in harrowing conditions by doing more helping capture prey and maintain webs more than male spiders, producing offspring who can work, or both. This advantage may explain the evolution of female-biased ratios in this very interesting yet very specific case.</p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">N</span>egative frequency-dependent selection acting on the sexes is hypothesized to drive populations towards a balanced sex ratio. However, numerous examples of female-biased sex ratios pepper the arthropods. Theoretical examinations have proposed that female-biased populations or groups can have higher chances of surviving and propagating, which may be advantageous. We evaluate this hypothesis in the semi-social spider, <i>Anelosimus studiosus</i>, by creating artificial colonies of varying sex ratios and sizes and observing colony performance at sites with high vs. low group extinction rates. We also tested whether colony extinction rates and sex ratios were correlated across 25 collection sites spanning 10º latitude. We found that colonies with female-biased sex ratios produced more egg cases and were more likely to survive the duration of a field season, suggesting that female-biased sex ratios confer both survival and reproductive advantages upon colonies. The effect of sex ratio on colony survival and reproductive output was strongest for small colonies in high extinction areas. Moreover, we found that female-biased sex ratios correlated with greater extinction rates across 25 sites, indicating that female-biased sex ratios may have evolved at some sites in response to high extinction rates. These findings suggest that selection favoring groups with female-biased sex ratios may operate in <i>A.&nbsp;studiosus</i>, shedding light on some of factors that may drive the evolution of biased sex ratios.</p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 24 Jul 2018 05:00:00 GMT