ASN RSS http://amnat.org/ Latest press releases and announcements from the ASN en-us Wed, 18 Jul 2018 05:00:00 GMT 60 “Dividing a maternal pie among half-sibs: genetic conflicts and the control of resource allocation to seeds in maize” http://amnat.org/an/newpapers/NovCailleau.html The DOI will be https://dx.doi.org/10.1086/699653 Sibling rivalry for maternal resource allocation: it also occurs in plants! Offspring size is a key fitness trait, which often results from various, possibly conflictual, interactions among parents and offspring. In angiosperms, seed mass is most often thought to result from maternal control. Paternal genotype and sibling rivalry is thought to play little role in this resource allocation. In this paper, Cailleau et al. present both a large-scale experiment and a new method to partition how the maternal sporophyte and half-sibs with different paternal genomes influence resource allocation. They find that the paternal genotypes in seeds influenced resource allocation by interacting with both the maternal plant and half-sibs. This paternal genotype influences the resource allocated to seed, often eliciting a greater maternal allocation than that observed upon selfing. They also find that there is strong sibling rivalry: maternal resources are allocated entirely competitively, and seeds with different paternal genotypes show different competitive ability to take up this resource. Furthermore, the researchers find evidence that competition between seeds with different paternal genotypes entails a cost and reduces the overall amount of resources allocated to the ear. These findings provide a better view of the control of resource allocation to seeds, which is essential for conflict theories, and may prove useful to optimize yield. Abstract Resource allocation to offspring is the battleground for various intra-familial conflicts. Understanding these conflicts requires knowledge of how the different actors (mother, siblings with different paternal genotypes) influence resource allocation. In angiosperms, resource to seeds is allocated post-fertilization and the paternally inherited genome in offspring can therefore influence resource allocation. However, the precise mode of resource allocation, and in particular the occurrence of sibling rivalry, has been rarely investigated in plants. In this paper, we develop a new method to analyze the resource allocation traits of the different actors (maternal sporophyte and half-sibs) using the data obtained from a large-scale diallel cross experiment in maize involving mixed hand pollination and colors markers to assess seed weight of known paternity. We found strong evidence for the occurrence of sibling rivalry: resources invested in an ear were allocated competitively and offspring with different paternal genotypes aggressively competed for this resource, entailing a measurable direct cost to the mother. We also show how resource allocation can be described for each genotype by two maternal (source effect, average sink responsiveness) and two offspring traits (ability to attract maternal resource, competitive ability towards siblings). We will discuss how these findings help understanding how genetic conflicts shape resource allocation traits in angiosperms. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699653 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699653">Read the Article</a></i> </p> --> <p><b>Sibling rivalry for maternal resource allocation: it also occurs in plants! </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;">O</span>ffspring size is a key fitness trait, which often results from various, possibly conflictual, interactions among parents and offspring. In angiosperms, seed mass is most often thought to result from maternal control. Paternal genotype and sibling rivalry is thought to play little role in this resource allocation. In this paper, Cailleau et al. present both a large-scale experiment and a new method to partition how the maternal sporophyte and half-sibs with different paternal genomes influence resource allocation. They find that the paternal genotypes in seeds influenced resource allocation by interacting with both the maternal plant and half-sibs. This paternal genotype influences the resource allocated to seed, often eliciting a greater maternal allocation than that observed upon selfing. They also find that there is strong sibling rivalry: maternal resources are allocated entirely competitively, and seeds with different paternal genotypes show different competitive ability to take up this resource. Furthermore, the researchers find evidence that competition between seeds with different paternal genotypes entails a cost and reduces the overall amount of resources allocated to the ear. These findings provide a better view of the control of resource allocation to seeds, which is essential for conflict theories, and may prove useful to optimize yield. </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;">R</span>esource allocation to offspring is the battleground for various intra-familial conflicts. Understanding these conflicts requires knowledge of how the different actors (mother, siblings with different paternal genotypes) influence resource allocation. In angiosperms, resource to seeds is allocated post-fertilization and the paternally inherited genome in offspring can therefore influence resource allocation. However, the precise mode of resource allocation, and in particular the occurrence of sibling rivalry, has been rarely investigated in plants. In this paper, we develop a new method to analyze the resource allocation traits of the different actors (maternal sporophyte and half-sibs) using the data obtained from a large-scale diallel cross experiment in maize involving mixed hand pollination and colors markers to assess seed weight of known paternity. We found strong evidence for the occurrence of sibling rivalry: resources invested in an ear were allocated competitively and offspring with different paternal genotypes aggressively competed for this resource, entailing a measurable direct cost to the mother. We also show how resource allocation can be described for each genotype by two maternal (source effect, average sink responsiveness) and two offspring traits (ability to attract maternal resource, competitive ability towards siblings). We will discuss how these findings help understanding how genetic conflicts shape resource allocation traits in angiosperms. </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, 10 Jul 2018 05:00:00 GMT “Disentangling pre- and post-natal maternal age effects on offspring performance in an insect with elaborate maternal care” http://amnat.org/an/newpapers/NovIvimeyC-A.html The DOI will be https://dx.doi.org/10.1086/699654 Abstract Maternal effect senescence has attracted much recent scientific interest. However, the age-related effects of pre- and post-natal maternal age are often conflated, as these naturally originate from the same individual. Additionally, many maternal effect senescence studies fail to account for potential biases associated with selective disappearance. Here we use a cross-fostered laboratory population of burying beetle, Nicrophorus vespilloides, to examine both the effects of female pre- and post-natal maternal age on offspring life history traits and the post-care outcomes of mothers while accounting for selective disappearance of post-natal caregivers. Neither pre- nor post-natal maternal age affected offspring longevity or larval weight at hatching, and post-natal age had no effect upon post-care maternal outcomes except to confirm the presence of actuarial senescence. There was weak evidence for concave relationships between two larval traits (dispersal weight and survival) and the age of egg-producers. Selective disappearance of caregivers had no clear effect on any of the measured offspring traits. Contrary to predictions from evolutionary theory, maternal effect senescence and reproductive effort increases do not always manifest, and current theory may be insufficient to account for the true diversity of aging patterns relating to maternal care. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699654 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699654">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;">M</span>aternal effect senescence has attracted much recent scientific interest. However, the age-related effects of pre- and post-natal maternal age are often conflated, as these naturally originate from the same individual. Additionally, many maternal effect senescence studies fail to account for potential biases associated with selective disappearance. Here we use a cross-fostered laboratory population of burying beetle, <i>Nicrophorus vespilloides</i>, to examine both the effects of female pre- and post-natal maternal age on offspring life history traits and the post-care outcomes of mothers while accounting for selective disappearance of post-natal caregivers. Neither pre- nor post-natal maternal age affected offspring longevity or larval weight at hatching, and post-natal age had no effect upon post-care maternal outcomes except to confirm the presence of actuarial senescence. There was weak evidence for concave relationships between two larval traits (dispersal weight and survival) and the age of egg-producers. Selective disappearance of caregivers had no clear effect on any of the measured offspring traits. Contrary to predictions from evolutionary theory, maternal effect senescence and reproductive effort increases do not always manifest, and current theory may be insufficient to account for the true diversity of aging patterns relating to maternal care. </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, 10 Jul 2018 05:00:00 GMT “Does population structure predict the rate of speciation? A comparative test across Australia's most diverse vertebrate radiation” http://amnat.org/an/newpapers/OctSinghal-A.html The DOI will be https://dx.doi.org/10.1086/699515 Abstract Population divergence is the first step in allopatric speciation, as has long been recognized in both theoretical models of speciation and empirical explorations of natural systems. All else being equal, lineages with substantial population differentiation should form new species more quickly than lineages that maintain range-wide genetic cohesion through high levels of gene flow. However, there have been few direct tests of the extent to which population differentiation predicts speciation rates as measured on phylogenetic trees. Here, we explicitly test the links between organismal traits, population-level processes, and phylogenetic speciation rates across a diverse clade of Australian lizards that shows remarkable variation in speciation rate. Using genome-wide ddRAD data from 892 individuals, we generated a comparative dataset on isolation-by-distance and population differentiation across 104 putative species-level lineages (OTUs). We find that species show substantial variation in the extent of population differentiation, and this variation is predicted by organismal traits that are thought to be proxies for dispersal and deme size. However, variation in population structure does not predict variation in speciation rate. Our results suggest that population differentiation is not the rate-limiting step in species formation and that other ecological and historical factors are primary determinants of speciation rates at macroevolutionary scales. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699515 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699515">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;">P</span>opulation divergence is the first step in allopatric speciation, as has long been recognized in both theoretical models of speciation and empirical explorations of natural systems. All else being equal, lineages with substantial population differentiation should form new species more quickly than lineages that maintain range-wide genetic cohesion through high levels of gene flow. However, there have been few direct tests of the extent to which population differentiation predicts speciation rates as measured on phylogenetic trees. Here, we explicitly test the links between organismal traits, population-level processes, and phylogenetic speciation rates across a diverse clade of Australian lizards that shows remarkable variation in speciation rate. Using genome-wide ddRAD data from 892 individuals, we generated a comparative dataset on isolation-by-distance and population differentiation across 104 putative species-level lineages (OTUs). We find that species show substantial variation in the extent of population differentiation, and this variation is predicted by organismal traits that are thought to be proxies for dispersal and deme size. However, variation in population structure does not predict variation in speciation rate. Our results suggest that population differentiation is not the rate-limiting step in species formation and that other ecological and historical factors are primary determinants of speciation rates at macroevolutionary scales. </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, 10 Jul 2018 05:00:00 GMT “Host dispersal responses to resource supplementation determine pathogen spread in wildlife metapopulations” http://amnat.org/an/newpapers/OctBecker.html The DOI will be https://dx.doi.org/10.1086/699477 How does resource supplementation and infection affect infectious disease spread in wildlife metapopulations? Urban parks, backyards, landfills, and agricultural fields provide wildlife with access to novel food sources. Food provided by humans in these locations can dramatically alter patterns of animal site fidelity and movement between habitats, with consequences for pathogen spread across the landscape. To better understand how the extent of food-subsidized habitat affects wildlife distributions and infection patterns, researchers at the University of Georgia developed a mathematical model that assumes that animal dispersal and the duration of site occupancy will depend on food availability and abundance at a given site as well as animal infection status. The authors found that both wildlife distributions across the landscape, and pathogen infection prevalence, depend on how productive food-provisioned patches are relative to natural patches. If habitats with human-provided food are occupied for longer by animals and produce more dispersers (such as might occur if animals survive better and produce more offspring when food is abundant and reliable), then infection becomes more widespread as more of the landscape is provisioned. However, if habitats with human-provided food produce fewer dispersers (such as might occur if animals stop moving as much when abundant food is present), then infection prevalence declines as more sites become provisioned. Reducing opportunities for pathogen spread can in turn increase landscape-level occupancy by wildlife. These results highlight that when wildlife are fed by humans, whether at landfills or through recreational wildlife feeding, this can alter the spread of pathogens across a landscape. To determine if food provisioning is beneficial or detrimental for wildlife abundance and health, future work is needed to examine how births, deaths, and movement behavior respond to human-provided resources. These results are especially applicable to highly mobile, nomadic, urban-feeding species such as flying foxes, white ibis (pictured), and many other birds and mammals. The research was led by Daniel Becker, a recent PhD graduate from the University of Georgia, overseen by University of Georgia faculty Sonia Altizer and Richard Hall, and resulted from a summer undergraduate research project from recent UC Berkeley undergraduate Celine Snedden. Abstract Many wildlife species occupy landscapes that vary in the distribution, abundance, and quality of food resources. Increasingly, urbanized and agricultural habitats provide supplemental food resources that can have profound consequences for host distributions, movement patterns, and pathogen exposure. Understanding how host and pathogen dispersal across landscapes is affected by the spatial extent of food-supplemented habitats is therefore important for predicting the consequences for pathogen spread and impacts on host occupancy. Here we develop a generalizable metapopulation model to understand how the relative abundance of provisioned habitats across the landscape, and host dispersal responses to provisioning and infection, influence patch occupancy by hosts and their pathogens. We find that pathogen invasion and landscape-level infection prevalence are greatest when provisioning increases patch attractiveness and disperser production and when infection has minimal costs on dispersal success. Alternatively, if provisioning promotes site fidelity or reduces disperser production, increasing the fraction of food-supplemented habitats can reduce landscape-scale infection prevalence and minimize disease-induced declines in host occupancy. This work highlights the importance of considering how resources and infection jointly influence host dispersal for predicting how changing resource distributions influence the spread of infectious diseases. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699477 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699477">Read the Article</a></i> </p> --> <p><b>How does resource supplementation and infection affect infectious disease spread in wildlife metapopulations? </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;">U</span>rban parks, backyards, landfills, and agricultural fields provide wildlife with access to novel food sources. Food provided by humans in these locations can dramatically alter patterns of animal site fidelity and movement between habitats, with consequences for pathogen spread across the landscape. To better understand how the extent of food-subsidized habitat affects wildlife distributions and infection patterns, researchers at the University of Georgia developed a mathematical model that assumes that animal dispersal and the duration of site occupancy will depend on food availability and abundance at a given site as well as animal infection status.</p> <p>The authors found that both wildlife distributions across the landscape, and pathogen infection prevalence, depend on how productive food-provisioned patches are relative to natural patches. If habitats with human-provided food are occupied for longer by animals and produce more dispersers (such as might occur if animals survive better and produce more offspring when food is abundant and reliable), then infection becomes more widespread as more of the landscape is provisioned. However, if habitats with human-provided food produce fewer dispersers (such as might occur if animals stop moving as much when abundant food is present), then infection prevalence declines as more sites become provisioned. Reducing opportunities for pathogen spread can in turn increase landscape-level occupancy by wildlife.</p> <p>These results highlight that when wildlife are fed by humans, whether at landfills or through recreational wildlife feeding, this can alter the spread of pathogens across a landscape. To determine if food provisioning is beneficial or detrimental for wildlife abundance and health, future work is needed to examine how births, deaths, and movement behavior respond to human-provided resources. These results are especially applicable to highly mobile, nomadic, urban-feeding species such as flying foxes, white ibis (pictured), and many other birds and mammals.</p> <p>The research was led by Daniel Becker, a recent PhD graduate from the University of Georgia, overseen by University of Georgia faculty Sonia Altizer and Richard Hall, and resulted from a summer undergraduate research project from recent UC Berkeley undergraduate Celine Snedden.</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;">M</span>any wildlife species occupy landscapes that vary in the distribution, abundance, and quality of food resources. Increasingly, urbanized and agricultural habitats provide supplemental food resources that can have profound consequences for host distributions, movement patterns, and pathogen exposure. Understanding how host and pathogen dispersal across landscapes is affected by the spatial extent of food-supplemented habitats is therefore important for predicting the consequences for pathogen spread and impacts on host occupancy. Here we develop a generalizable metapopulation model to understand how the relative abundance of provisioned habitats across the landscape, and host dispersal responses to provisioning and infection, influence patch occupancy by hosts and their pathogens. We find that pathogen invasion and landscape-level infection prevalence are greatest when provisioning increases patch attractiveness and disperser production and when infection has minimal costs on dispersal success. Alternatively, if provisioning promotes site fidelity or reduces disperser production, increasing the fraction of food-supplemented habitats can reduce landscape-scale infection prevalence and minimize disease-induced declines in host occupancy. This work highlights the importance of considering how resources and infection jointly influence host dispersal for predicting how changing resource distributions influence the spread of infectious diseases.</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, 10 Jul 2018 05:00:00 GMT “Rising temperatures, molting phenology and epizootic shell disease in the American lobster” http://amnat.org/an/newpapers/NovGroner.html The DOI will be https://dx.doi.org/10.1086/699478 Rising temperatures cause phenological mismatch between molting and epizootic shell disease in the American lobster Changing environmental conditions can alter the timing of key events during a species’ lifetime. In some cases this can cause a mismatch between an event and critical environmental or biological conditions. This ‘phenological mismatch’ has been investigated in a variety of scenarios such as the timing of breeding and migration with food availability and predation risk. However, it has not been well examined in the context of disease risk. In this paper, the authors’ investigated how changing seawater temperature is altering responses to an emerging disease of the American lobster, epizootic shell disease (ESD). Using a 34-year mark-recapture dataset from Long Island Sound, CT, the authors investigated relationships between seawater temperature, molting phenology, and seasonal variation of epizootic shell disease (ESD). ESD is an emerging disease of lobsters caused by a suite of bacteria on the lobster cuticle that feed upon materials in the shell. Molting can be beneficial for diseased lobsters because it allows them to discard their diseased shell. The authors’ analyses support the hypothesis that phenological mismatch is linked to seasonal variation in ESD. They found that warmer spring temperatures were associated with earlier spring molting. This increased the length of the intermolt period in the summer, when disease transmission is highest. For juvenile and adult male lobsters, earlier molting was associated with a greater proportion of diseased lobsters in September; however, in October, the proportion of diseased lobsters was most strongly associated with warmer summer seawater temperature. This suggests that spring temperatures affect the timing of the onset of disease by altering molting patterns, but, over time, this signal is swamped by the stronger signal of summer temperatures. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Population impacts of ESD are expected to increase with increasing seawater temperatures. Abstract Phenological mismatch, maladaptive changes in phenology resulting from altered timing of environmental cues, is an increasing concern in many ecological systems, yet its effects on disease are poorly characterized. American lobster (Homarus americanus) is declining at its southern geographic limit. Rising seawater temperatures are associated with seasonal outbreaks of epizootic shell disease (ESD), which peaks in prevalence in the fall. We used a 34-year mark-recapture dataset to investigate relationships between temperature, molting phenology, and ESD in Long Island Sound, where temperatures are increasing at 0.4&thinsp;&deg;C per decade. Our analyses support the hypothesis that phenological mismatch is linked to the epidemiology of ESD. Warming spring temperatures are correlated with earlier spring molting. Lobsters lose diseased cuticle by molting, and early molting increases the intermolt period in the summer, when disease prevalence is increasing to a fall peak. In juvenile and adult male lobsters, September ESD prevalence was correlated with early molting, while October ESD prevalence was correlated with summer seawater temperature. This suggests that temperature-induced molting phenology affects the timing of the onset of ESD, but, later in the summer, this signal is swamped by the stronger signal of summer temperatures, which we hypothesize are associated with an increased rate of new infections. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Yearly survival of diseased lobsters is <50% that of healthy lobsters. Thus, population impacts of ESD are expected to increase with increasing seawater temperatures. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699478 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699478">Read the Article</a></i> </p> --> <p><b>Rising temperatures cause phenological mismatch between molting and epizootic shell disease in the American lobster </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;">C</span>hanging environmental conditions can alter the timing of key events during a species&rsquo; lifetime. In some cases this can cause a mismatch between an event and critical environmental or biological conditions. This &lsquo;phenological mismatch&rsquo; has been investigated in a variety of scenarios such as the timing of breeding and migration with food availability and predation risk. However, it has not been well examined in the context of disease risk.</p> <p>In this paper, the authors&rsquo; investigated how changing seawater temperature is altering responses to an emerging disease of the American lobster, epizootic shell disease (ESD). Using a 34-year mark-recapture dataset from Long Island Sound, CT, the authors investigated relationships between seawater temperature, molting phenology, and seasonal variation of epizootic shell disease (ESD). ESD is an emerging disease of lobsters caused by a suite of bacteria on the lobster cuticle that feed upon materials in the shell. Molting can be beneficial for diseased lobsters because it allows them to discard their diseased shell.</p> <p>The authors&rsquo; analyses support the hypothesis that phenological mismatch is linked to seasonal variation in ESD. They found that warmer spring temperatures were associated with earlier spring molting. This increased the length of the intermolt period in the summer, when disease transmission is highest. For juvenile and adult male lobsters, earlier molting was associated with a greater proportion of diseased lobsters in September; however, in October, the proportion of diseased lobsters was most strongly associated with warmer summer seawater temperature. This suggests that spring temperatures affect the timing of the onset of disease by altering molting patterns, but, over time, this signal is swamped by the stronger signal of summer temperatures. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Population impacts of ESD are expected to increase with increasing seawater temperatures.</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;">P</span>henological mismatch, maladaptive changes in phenology resulting from altered timing of environmental cues, is an increasing concern in many ecological systems, yet its effects on disease are poorly characterized. American lobster (<i>Homarus americanus</i>) is declining at its southern geographic limit. Rising seawater temperatures are associated with seasonal outbreaks of epizootic shell disease (ESD), which peaks in prevalence in the fall. We used a 34-year mark-recapture dataset to investigate relationships between temperature, molting phenology, and ESD in Long Island Sound, where temperatures are increasing at 0.4&thinsp;&deg;C per decade. Our analyses support the hypothesis that phenological mismatch is linked to the epidemiology of ESD. Warming spring temperatures are correlated with earlier spring molting. Lobsters lose diseased cuticle by molting, and early molting increases the intermolt period in the summer, when disease prevalence is increasing to a fall peak. In juvenile and adult male lobsters, September ESD prevalence was correlated with early molting, while October ESD prevalence was correlated with summer seawater temperature. This suggests that temperature-induced molting phenology affects the timing of the onset of ESD, but, later in the summer, this signal is swamped by the stronger signal of summer temperatures, which we hypothesize are associated with an increased rate of new infections. October ESD prevalence was ~80% in years with hot summers, and ~30% in years with cooler summers. Yearly survival of diseased lobsters is &lt;50% that of healthy lobsters. Thus, population impacts of ESD are expected to increase with increasing seawater temperatures.</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, 10 Jul 2018 05:00:00 GMT “Coevolution slows the disassembly of mutualistic networks” http://amnat.org/an/newpapers/OctNuismer2018-A.html The DOI will be https://dx.doi.org/10.1086/699218 Disassembly of mutualistic networks is slowed by historical coevolution and mitigated by coevolutionary rescue Abstract Important groups of mutualistic species are threatened worldwide, and identifying factors that make them more or less fragile in the face of disturbance is becoming increasingly critical. Although much research has focused on identifying the ecological factors that favor the stability of communities rich in mutualists, much less has been devoted to understanding the role of historical and contemporary evolution. Here we develop mathematical models and computer simulations of coevolving mutualistic communities that allow us to explore the importance of coevolution in stabilizing communities against anthropogenic disturbance. Our results demonstrate that communities with a long history of coevolution are substantially more robust to disturbance, losing individual species and interactions at lower rates. In addition, our results identify a novel phenomenon – coevolutionary rescue – that mitigates the impacts of ongoing anthropogenic disturbance by re-wiring the network structure of the community in a way that compensates for the extinction of individual species and interactions. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699218 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699218">Read the Article</a></i> </p> --> <p><b>Disassembly of mutualistic networks is slowed by historical coevolution and mitigated by coevolutionary rescue </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;">I</span>mportant groups of mutualistic species are threatened worldwide, and identifying factors that make them more or less fragile in the face of disturbance is becoming increasingly critical. Although much research has focused on identifying the ecological factors that favor the stability of communities rich in mutualists, much less has been devoted to understanding the role of historical and contemporary evolution. Here we develop mathematical models and computer simulations of coevolving mutualistic communities that allow us to explore the importance of coevolution in stabilizing communities against anthropogenic disturbance. Our results demonstrate that communities with a long history of coevolution are substantially more robust to disturbance, losing individual species and interactions at lower rates. In addition, our results identify a novel phenomenon – coevolutionary rescue – that mitigates the impacts of ongoing anthropogenic disturbance by re-wiring the network structure of the community in a way that compensates for the extinction of individual species and interactions. </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, 28 Jun 2018 05:00:00 GMT “The role of geography in adaptive radiation” http://amnat.org/an/newpapers/OctSchenk.html The DOI will be https://dx.doi.org/10.1086/699221 Biogeographic transitions are important drivers of species diversity in adaptive radiations To explain why millions of species exist on Earth, biologists seek to discover how species evolve and the factors promoting diversification. Of particular interest are groups of closely related species that rapidly evolved many new species as they adapted to new niches, a process called adaptive radiation. Even though adaptive radiation is the most iconic process in the diversification of life (most famously in the Galapagos finches), most well-studied cases occur on islands, and we know relatively little about how or if these radiations occur on continents, where most species actually live. In the absence of obvious barriers like oceanic waters, how does diversification proceed across the continuous geography of a continent? Does it start in one region, slowly spreading out as species adapt to each new habitat in turn, or does it spread everywhere quickly, and only evolve adaptations later? In their study, Schenk and Steppan develop a new approach to examine how speciation proceeds across geographic space by studying 300 species from one of the most diverse groups of mammals, the South American sigmodontine rodents. Sigmodontines experienced an adaptive radiation following their colonization from North America approximately seven million years ago. Soon after colonizing South America, they expanded into many new regions quickly at the same time as they had a burst of diversification, and their dispersal across the heterogeneous landscape was important to their adaptive radiation. As time passed, both the rate of geographic dispersal and speciation slowed down in concert. While ecological divergence into different niches is important during adaptive radiations, movement into new and distinctive geographic regions allows speciation to repeatedly reoccur and can promote the remarkable biodiversity characteristic of adaptive radiations. Abstract Although the importance of biogeography in the speciation process is well-recognized, the fundamental role of geographic diversification during adaptive radiations has not been studied to determine its importance during the adaptive radiation process. We examined the relationship between lineage and regional diversification patterns in the South American rodent subfamily Sigmodontinae, one of the best candidates for an adaptive radiation in mammals, to propose a conceptual framework for geographic transitions during adaptive radiations. We reconstructed a time-calibrated phylogeny from four nuclear and one mitochondrial gene for 77% of sigmodontine diversity. Historical biogeography was reconstructed among 14 regions, to which we applied a sliding-window approach to estimate regional transition rates through time. We compared these rate patterns and measured whether regions consisted of species that were more phylogenetically related than expected by chance. Following the initial South American colonization around 7 million years ago, multiple expansions from northern regions correlated with a burst of speciation. Subsequently, both diversification and regional transition rates decreased overall and within the majority of regions. Despite high regional transition rates, nearly all regional assemblages were phylogenetically clustered, indicating within-region diversification was common. We conclude that biogeographic complexity and partitioning played a profound role in the adaptive radiation of the South American Sigmodontinae (Oryzomyalia), the degree to which is determined by the relative scales of spatial variation and dispersal abilities. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699221 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699221">Read the Article</a></i> </p> --> <p><b>Biogeographic transitions are important drivers of species diversity in adaptive radiations </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>o explain why millions of species exist on Earth, biologists seek to discover how species evolve and the factors promoting diversification. Of particular interest are groups of closely related species that rapidly evolved many new species as they adapted to new niches, a process called adaptive radiation. Even though adaptive radiation is the most iconic process in the diversification of life (most famously in the Galapagos finches), most well-studied cases occur on islands, and we know relatively little about how or if these radiations occur on continents, where most species actually live. In the absence of obvious barriers like oceanic waters, how does diversification proceed across the continuous geography of a continent? Does it start in one region, slowly spreading out as species adapt to each new habitat in turn, or does it spread everywhere quickly, and only evolve adaptations later?</p> <p>In their study, Schenk and Steppan develop a new approach to examine how speciation proceeds across geographic space by studying 300 species from one of the most diverse groups of mammals, the South American sigmodontine rodents. Sigmodontines experienced an adaptive radiation following their colonization from North America approximately seven million years ago. Soon after colonizing South America, they expanded into many new regions quickly at the same time as they had a burst of diversification, and their dispersal across the heterogeneous landscape was important to their adaptive radiation. As time passed, both the rate of geographic dispersal and speciation slowed down in concert. While ecological divergence into different niches is important during adaptive radiations, movement into new and distinctive geographic regions allows speciation to repeatedly reoccur and can promote the remarkable biodiversity characteristic of adaptive radiations.</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;">A</span>lthough the importance of biogeography in the speciation process is well-recognized, the fundamental role of geographic diversification during adaptive radiations has not been studied to determine its importance during the adaptive radiation process. We examined the relationship between lineage and regional diversification patterns in the South American rodent subfamily Sigmodontinae, one of the best candidates for an adaptive radiation in mammals, to propose a conceptual framework for geographic transitions during adaptive radiations. We reconstructed a time-calibrated phylogeny from four nuclear and one mitochondrial gene for 77% of sigmodontine diversity. Historical biogeography was reconstructed among 14 regions, to which we applied a sliding-window approach to estimate regional transition rates through time. We compared these rate patterns and measured whether regions consisted of species that were more phylogenetically related than expected by chance. Following the initial South American colonization around 7 million years ago, multiple expansions from northern regions correlated with a burst of speciation. Subsequently, both diversification and regional transition rates decreased overall and within the majority of regions. Despite high regional transition rates, nearly all regional assemblages were phylogenetically clustered, indicating within-region diversification was common. We conclude that biogeographic complexity and partitioning played a profound role in the adaptive radiation of the South American Sigmodontinae (Oryzomyalia), the degree to which is determined by the relative scales of spatial variation and dispersal abilities.</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> Thu, 28 Jun 2018 05:00:00 GMT “Environmental stress increases the magnitude of non-additive genetic variation in offspring fitness in the frog Crinia georgiana” http://amnat.org/an/newpapers/OctRudinB-A.html The DOI will be https://dx.doi.org/10.1086/699231 Environmental stress increases the magnitude of non-additive genetic variation in offspring fitness in a frog Abstract When organisms encounter heterogeneous environments, selection may favor the ability of individuals to tailor their phenotypes to suit the prevailing conditions. Understanding the genetic basis of plastic responses is therefore vital for predicting whether susceptible populations can adapt and persist under new selection pressures. Here, we investigated whether there is potential for adaptive plasticity in development time in the quacking frog Crinia georgiana, a species experiencing a drying climate. Using a North Carolina II breeding design, we exposed 90 family groups to two water depth treatments (baseline and low-water) late in larval development. We then estimated the contribution of additive and non-additive sources of genetic variation to early offspring fitness under both environments. Our results revealed a marked decline in larval fitness under the stressful (low-water) rearing environment, but also that additive genetic variation was negligible for all traits. However, in most cases we found significant sire-by-dam interactions, indicating the importance of non-additive genetic variation for offspring fitness. Moreover, sire-by-dam interactions were modified by the treatment, indicating that patterns of non-additive genetic variance depend on environmental context. For all traits, we found higher levels of non-additive genetic variation (relative to total phenotypic variation) when larvae were reared under stressful conditions, suggesting that the fitness costs associated with incompatible parental crosses (e.g. homozygous deleterious recessive alleles) will only be expressed when water availability is low. Taken together, our results highlight the need to consider patterns of non-additive genetic variation under contrasting selective regimes when considering the resilience of species to environmental change. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699231 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699231">Read the Article</a></i> </p> --> <p><b>Environmental stress increases the magnitude of non-additive genetic variation in offspring fitness in a frog </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;">W</span>hen organisms encounter heterogeneous environments, selection may favor the ability of individuals to tailor their phenotypes to suit the prevailing conditions. Understanding the genetic basis of plastic responses is therefore vital for predicting whether susceptible populations can adapt and persist under new selection pressures. Here, we investigated whether there is potential for adaptive plasticity in development time in the quacking frog <i>Crinia georgiana</i>, a species experiencing a drying climate. Using a North Carolina II breeding design, we exposed 90 family groups to two water depth treatments (baseline and low-water) late in larval development. We then estimated the contribution of additive and non-additive sources of genetic variation to early offspring fitness under both environments. Our results revealed a marked decline in larval fitness under the stressful (low-water) rearing environment, but also that additive genetic variation was negligible for all traits. However, in most cases we found significant sire-by-dam interactions, indicating the importance of non-additive genetic variation for offspring fitness. Moreover, sire-by-dam interactions were modified by the treatment, indicating that patterns of non-additive genetic variance depend on environmental context. For all traits, we found higher levels of non-additive genetic variation (relative to total phenotypic variation) when larvae were reared under stressful conditions, suggesting that the fitness costs associated with incompatible parental crosses (e.g. homozygous deleterious recessive alleles) will only be expressed when water availability is low. Taken together, our results highlight the need to consider patterns of non-additive genetic variation under contrasting selective regimes when considering the resilience of species to environmental change.</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> Thu, 28 Jun 2018 05:00:00 GMT “Competition and ‘stragglers’ as mediators of developmental synchrony in periodical cicadas” http://amnat.org/an/newpapers/OctBlackwood-A.html The DOI will be https://dx.doi.org/10.1086/699255 Abstract Periodical cicadas are enigmatic organisms: broods spanning large spatial ranges consist of developmentally synchronized populations of 3-4 sympatric species that emerge as adults every 13 or 17 years. Only one brood typically occupies any single location, with well-defined boundaries separating distinct broods. The cause of such synchronous development remains uncertain but it is known that synchronous emergence of large numbers of adults in a single year satiates predators, allowing a substantial fraction of emerging adults to survive long enough to reproduce. Competition among nymphs feeding on tree roots almost certainly plays a role in limiting populations. However, due to the difficulty of working with such long-lived subterranean life stages, the mechanisms governing competition in periodical cicadas have not been identified. A second process that may affect synchrony among periodical cicadas is their ability to delay or accelerate their emergence as adults by one year and accelerate it by four years (“stragglers”). We develop a non-linear Leslie-type matrix model that describes cicada dynamics accounting for predation, competition and stragglers. Using numerical simulations, we identify conditions that generate dynamics in which a single brood occupies a given geographical location. Our results show that while stragglers have potential for introducing multiple sympatric broods, the interaction of interbrood competition with predation-driven Allee effects creates a system resistant to such invasions and populations maintain developmental synchrony. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/699255 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/699255">Read the Article</a></i> </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;">P</span>eriodical cicadas are enigmatic organisms: broods spanning large spatial ranges consist of developmentally synchronized populations of 3-4 sympatric species that emerge as adults every 13 or 17 years. Only one brood typically occupies any single location, with well-defined boundaries separating distinct broods. The cause of such synchronous development remains uncertain but it is known that synchronous emergence of large numbers of adults in a single year satiates predators, allowing a substantial fraction of emerging adults to survive long enough to reproduce. Competition among nymphs feeding on tree roots almost certainly plays a role in limiting populations. However, due to the difficulty of working with such long-lived subterranean life stages, the mechanisms governing competition in periodical cicadas have not been identified. A second process that may affect synchrony among periodical cicadas is their ability to delay or accelerate their emergence as adults by one year and accelerate it by four years (&ldquo;stragglers&rdquo;). We develop a non-linear Leslie-type matrix model that describes cicada dynamics accounting for predation, competition and stragglers. Using numerical simulations, we identify conditions that generate dynamics in which a single brood occupies a given geographical location. Our results show that while stragglers have potential for introducing multiple sympatric broods, the interaction of interbrood competition with predation-driven Allee effects creates a system resistant to such invasions and populations maintain developmental synchrony.</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> Thu, 28 Jun 2018 05:00:00 GMT Joint Societies Letter to the EPA on Using All Available Data http://amnat.org/announcements/LTREPA.html On behalf of the Society for the Study of Evolution, the American Society of Naturalists, and the Society of Systematic Biologists (over 4600 members in total), we are writing to express significant concerns regarding the proposed EPA rule&nbsp; announced on April 24, 2018. The proposed rule would mandate that research conducted by the EPA must be based on data that are publicly available. The rationale for the proposed revision is that it is &#39;intended to strengthen the transparency of EPA regulatory science&#39; through ensuring &#39;that the data underlying those are publicly available in a manner sufficient for independent validation.&#39; In effect, the proposed rule would severely limit the type of data able to be used by EPA scientists:&nbsp; it would restrict them to use only data made publicly available by parties that may be affected about the outcome of EPA research, and it would restrict EPA scientists from using data that has proprietary information, patient confidentiality issues, or other ethical restrictions to the dissemination of confidential information.&nbsp; In short, it could bias the data used by EPA scientists, preventing objective analysis and resulting policy recommendations. We agree that data transparency strengthens the rigor of published scientific work. However, there are certain cases in which data cannot be made public, for example when they contain personal identifiers. In such cases, the proposed rule could unduly remove the use of otherwise appropriate data from scientific studies, significantly limiting the types of data used to inform decisions on public and environmental health. The scientific community has a high standard of scientific rigor and has already instituted mechanisms to deal with cases in which not all data can be made public. Prior to publication, peer reviewers can sometimes have access to confidential information. Both before and after publication, work is evaluated by scientific peers on the appropriateness and clarity of the methods that were used, the analysis that was performed, and the logical interpretation of the results. Lastly, data are shared with specific researchers who seek to replicate or build upon the published work. Decisions are best made when all evidence is considered. Peer reviewed evidence has passed a high level of rigor. Excluding studies because their associated data contain specific confidential details will make it more difficult for the EPA to act in the best interest of the public and the environment. We are deeply concerned that this rule will significantly bias the information that is used, resulting in poor policy decisions. Sincerely, &nbsp; Dr. Hopi Hoekstra; President, Society for the Study of Evolution Dr. Sharon Strauss; President, American Society of Naturalists Dr. Susana Magall&oacute;n; President, Society of Systematic Biologists &nbsp; [1] U.S. Environmental Protection Agency, News Release (2018), “EPA Administrator Pruitt proposes rule to strengthen science used In EPA regulations”; www.epa.gov/newsreleases/epa-administrator-pruitt-proposes-rule-strengthen-science-used-epa-regulations. <p>On behalf of the Society for the Study of Evolution, the American Society of Naturalists, and the Society of Systematic Biologists (over 4600 members in total), we are writing to express significant concerns regarding the proposed EPA rule&nbsp; announced on April 24, 2018.</p> <p>The proposed rule would mandate that research conducted by the EPA must be based on data that are publicly available. The rationale for the proposed revision is that it is &#39;intended to strengthen the transparency of EPA regulatory science&#39; through ensuring &#39;that the data underlying those are publicly available in a manner sufficient for independent validation.&#39; In effect, the proposed rule would severely limit the type of data able to be used by EPA scientists:&nbsp; it would restrict them to use only data made publicly available by parties that may be affected about the outcome of EPA research, and it would restrict EPA scientists from using data that has proprietary information, patient confidentiality issues, or other ethical restrictions to the dissemination of confidential information.&nbsp; In short, it could bias the data used by EPA scientists, preventing objective analysis and resulting policy recommendations.</p> <p>We agree that data transparency strengthens the rigor of published scientific work. However, there are certain cases in which data cannot be made public, for example when they contain personal identifiers. In such cases, the proposed rule could unduly remove the use of otherwise appropriate data from scientific studies, significantly limiting the types of data used to inform decisions on public and environmental health.</p> <p>The scientific community has a high standard of scientific rigor and has already instituted mechanisms to deal with cases in which not all data can be made public. Prior to publication, peer reviewers can sometimes have access to confidential information. Both before and after publication, work is evaluated by scientific peers on the appropriateness and clarity of the methods that were used, the analysis that was performed, and the logical interpretation of the results. Lastly, data are shared with specific researchers who seek to replicate or build upon the published work.</p> <p>Decisions are best made when all evidence is considered. Peer reviewed evidence has passed a high level of rigor. Excluding studies because their associated data contain specific confidential details will make it more difficult for the EPA to act in the best interest of the public and the environment. We are deeply concerned that this rule will significantly bias the information that is used, resulting in poor policy decisions.</p> <p>Sincerely,<br /> &nbsp;<br /> Dr. Hopi Hoekstra; President, Society for the Study of Evolution<br /> Dr. Sharon Strauss; President, American Society of Naturalists<br /> Dr. Susana Magall&oacute;n; President, Society of Systematic Biologists</p> <p>&nbsp;</p> <p>[1] U.S. Environmental Protection Agency, News Release (2018), &ldquo;EPA Administrator Pruitt proposes rule to strengthen science used In EPA regulations&rdquo;; <a href="http://www.epa.gov/newsreleases/epa-administrator-pruitt-proposes-rule-strengthen-science-used-epa-regulations" target="_blank">www.epa.gov/newsreleases/epa-administrator-pruitt-proposes-rule-strengthen-science-used-epa-regulations</a>.</p> Tue, 19 Jun 2018 05:00:00 GMT Links to the ASN Policy Statements http://amnat.org/announcements/Policy.html Joint Societies Letter to the EPA on Using All Available Data Letter to the NSF about the Doctoral Dissertation Improvement Grant Program ASN Attends Congressional Visits Day 2017 Letter to the U.S. Congress on the Endangered Species Act Letter to the U.S. Congress on Plant Conservation Legislation Joint Societies&#39; Letter to the Trump Administration on Travel Restrictions Letter to the US Congress on Proposed Tax Cuts and Jobs Act <ul> <li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://www.amnat.org/announcements/LTREPA.html">Joint Societies Letter to the EPA on Using All Available Data</a></h2> </li><li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://www.amnat.org/announcements/LTRDDIG.html">Letter to the NSF about the Doctoral Dissertation Improvement Grant Program</a></h2> </li> <li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://www.amnat.org/announcements/ReportAIBS.html">ASN Attends Congressional Visits Day 2017</a></h2> </li> <li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://www.amnat.org/announcements/LTRspecies.html">Letter to the U.S. Congress on the Endangered Species Act</a></h2> </li> <li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://www.amnat.org/announcements/LTRplant.html">Letter to the U.S. Congress on Plant Conservation Legislation</a></h2> </li> <li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://www.amnat.org/announcements/LTRvisa.html">Joint Societies&#39; Letter to the Trump Administration on Travel Restrictions</a></h2> </li> <li> <h2 style="margin: 0px; padding: 0px; font-size: 24px; color: rgb(0, 88, 37); font-family: Georgia, Georgia, &quot;Times New Roman&quot;, Times, serif; line-height: 31.2px; text-decoration: none; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(235, 253, 255);"><a href="http://amnat.org/announcements/LTRTuitionTax.html">Letter to the US Congress on Proposed Tax Cuts and Jobs Act</a></h2> </li> </ul> Tue, 19 Jun 2018 05:00:00 GMT ASN Stand-alone Meeting 2020 http://amnat.org/announcements/ASNAsilomar.html Planning for stand-alone meetings requires a two-year lead time.&nbsp; We had feedback from some attendees at the 2018 meeting that they would like the meeting to move around the country more.&nbsp; Unfortunately, the lead time was too short to change venues for the the 2020 meeting, we will again meet in Asilomar. Casey ter Horst has generously agreed to organize this meeting. We are actively looking NOW for organizers and venues in other parts of the country for the 2022 meetings. Please make suggestions! To recap: we need a venue that can accommodate 220 people, with approx. 7 smaller meeting rooms, one large room that can accommodate all present, joint eating facilities, and that ideally is located in a nice natural setting, in a place that is pleasant outside in January and not prohibitively expensive. These are harder criteria to meet than one might imagine. Anyone with suggestions for either organizer or venue, please contact Sharon Strauss (systrauss@ucdavis.edu) and Michael Whitlock (whitlock@zoology.ubc.ca) &nbsp; <p>Planning for stand-alone meetings requires a two-year lead time.&nbsp; We had feedback from some attendees at the 2018 meeting that they would like the meeting to move around the country more.&nbsp; Unfortunately, the lead time was too short to change venues for the the 2020 meeting, we will again meet in Asilomar. Casey ter Horst has generously agreed to organize this meeting.</p> <p>We are actively looking NOW for organizers and venues in other parts of the country for the 2022 meetings. Please make suggestions!</p> <p>To recap: we need a venue that can accommodate 220 people, with approx. 7 smaller meeting rooms, one large room that can accommodate all present, joint eating facilities, and that ideally is located in a nice natural setting, in a place that is pleasant outside in January and not prohibitively expensive. These are harder criteria to meet than one might imagine.</p> <p>Anyone with suggestions for either organizer or venue, please contact Sharon Strauss (<a href="mailto:systrauss@ucdavis.edu?subject=Stand-Alone%20Meeting%20Location">systrauss@ucdavis.edu</a>) and Michael Whitlock (<a href="mailto:whitlock@zoology.ubc.ca?subject=Stand-Alone%20Meeting%20Location">whitlock@zoology.ubc.ca</a>)</p> <p>&nbsp;</p> Tue, 19 Jun 2018 05:00:00 GMT “Introgression across hybrid zones is not mediated by Large X-effects in green toads with undifferentiated sex chromosomes” http://amnat.org/an/newpapers/NovGerchen-A.html Abstract Divergence between incipient species remains an incompletely understood process. Hybrid zones provide great research potential, reflecting natural organismal genomic interactions and gene evolution in a variety of recombinants over generations. While sex chromosomes are known evolutionary drivers of reproductive isolation, empirical population genetics mostly examined species with heteromorphic sex chromosomes. We recently reported restricted introgression at sex-linked markers in an amphibian system with homomorphic sex chromosomes (Hyla), consistent with a Large X-effect, designating a greater role of sex chromosomes in driving hybrid incompatibilities. Here, using a similar approach, we examined two hybrid zones of Palearctic green toads (Bufo viridis subgroup), involving several lineages that arose at different times and form secondary contacts. We find no evidence for differential introgression of sex-linked vs. autosomal markers across both zones. This absence of Large X-effects in Bufo indicates that, unlike in Hyla, hybrid incompatibilities may not result from faster-heterogametic sex and faster-male aspects of Haldane’s rule. The recent suppression of XY recombination in Hyla, but not in Bufo, may have driven greater divergence between Hyla sex chromosomes, causing stronger reproductive isolation. Alternatively, stronger linkage among Hyla’s sex-linked markers could restrict introgression. We hypothesize that the degree of sex-specific recombination may condition the importance of homomorphic sex chromosomes in speciation. More forthcoming papers &raquo; <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>ivergence between incipient species remains an incompletely understood process. Hybrid zones provide great research potential, reflecting natural organismal genomic interactions and gene evolution in a variety of recombinants over generations. While sex chromosomes are known evolutionary drivers of reproductive isolation, empirical population genetics mostly examined species with heteromorphic sex chromosomes. We recently reported restricted introgression at sex-linked markers in an amphibian system with homomorphic sex chromosomes (<i>Hyla</i>), consistent with a Large X-effect, designating a greater role of sex chromosomes in driving hybrid incompatibilities. Here, using a similar approach, we examined two hybrid zones of Palearctic green toads (<i>Bufo viridis</i> subgroup), involving several lineages that arose at different times and form secondary contacts. We find no evidence for differential introgression of sex-linked vs. autosomal markers across both zones. This absence of Large X-effects in <i>Bufo</i> indicates that, unlike in <i>Hyla</i>, hybrid incompatibilities may not result from <i>faster-heterogametic sex</i> and <i>faster-male</i> aspects of Haldane’s rule. The recent suppression of XY recombination in <i>Hyla</i>, but not in <i>Bufo</i>, may have driven greater divergence between <i>Hyla</i> sex chromosomes, causing stronger reproductive isolation. Alternatively, stronger linkage among <i>Hyla</i>’s sex-linked markers could restrict introgression. We hypothesize that the degree of sex-specific recombination may condition the importance of homomorphic sex chromosomes in speciation. </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> Mon, 11 Jun 2018 05:00:00 GMT “Collective action promoted by key individuals” http://amnat.org/an/newpapers/OctWheatcroft.html The DOI will be https://dx.doi.org/10.1086/698874 High-gain individuals help form cooperative groups by incentivizing low-gain individuals to join A&nbsp;farmer rushes out of her house to confront a bear raiding her crops. She is soon followed by her neighbor, and together they succeed in scaring the bear away. The next day, the farmer is at the market when the bear comes again. This time, the bear has a feast while the neighbor watches on. Why might the neighbor join with another to perform an action she would not do on her own, especially given she would also benefit if the bear is driven away from the general vicinity? Complicated explanations, such as that of reciprocal altruism (“I help you now in the expectation you will help me later”) prevail in the literature. A simpler one comes with two conditions. First, the benefits should outweigh the costs for some individuals (i.e., the farmer) who perform the behavior even when alone. Second, once one individual is performing the behavior, the costs for others (i.e., the neighbor) are sufficiently reduced so that they are outweighed by the benefits. David Wheatcroft and Trevor Price asked if this idea can explain cooperative behaviors in nature. They studied responses of small birds to various enemies over four years in the western Himalayas. Crows prey upon the eggs and chicks of small birds, and cuckoos parasitize their nests. Wheatcroft and Price used taxidermied mounts of crows and cuckoos to show that, when acting alone, the only individuals to strongly attack the mounts were those with nests nearby. As long as nest owners are present, birds without nearby nests also join. By contrast, hawk and owl mounts are always vigorously attacked. Wheatcroft and Price then developed a theory of changing cost:benefit relationships, assuming the principles outlined above apply. They show that the results are as expected if crows and cuckoos are not too costly to attack and costs decline with the number of birds attacking the mount, but benefits always accrue to individuals attacking hawks and owls. Simple mechanisms (i.e., join if you benefit) may regularly explain the formation of cooperative groups. Abstract Explaining why individuals participate in risky group behaviors has been a long-term challenge. We experimentally studied the formation of groups of birds (“mobs”) that aggressively confront predators and avian nest parasites and developed a theoretical model to evaluate the conditions under which mobs arise. We presented taxidermied mounts of predators on adult birds (hawks and owls) and of nest threats (crows and cuckoos) at different distances to nests of Phylloscopus warblers. Even when alone, birds are aggressive towards predators of adult birds, both at and away from their nests. By contrast, birds aggressively confront nest threats alone only when they have a nest nearby. However, strong initial responses by nest owners lead individuals without nearby nests to increase their responses, thereby generating a mob. Building on these findings, we derive the conditions when individuals are incentivized to invest more when joining a high-gain individual compared to when acting alone. Strong responses of high-gain individuals acting alone tend to reduce the investments of other high-gain individuals that subsequently join. However, individuals that benefit sufficiently little from acting alone increase their investments when joining a high-gain individual and can even be sufficiently incentivized to join in when they would otherwise not act alone. Together, these results suggest an important role for key individuals in the generation of some group behaviors. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698874 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698874">Read the Article</a></i> </p> --> <p><b>High-gain individuals help form cooperative groups by incentivizing low-gain individuals to join </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;farmer rushes out of her house to confront a bear raiding her crops. She is soon followed by her neighbor, and together they succeed in scaring the bear away. The next day, the farmer is at the market when the bear comes again. This time, the bear has a feast while the neighbor watches on. Why might the neighbor join with another to perform an action she would not do on her own, especially given she would also benefit if the bear is driven away from the general vicinity? Complicated explanations, such as that of reciprocal altruism (“I help you now in the expectation you will help me later”) prevail in the literature. A simpler one comes with two conditions. First, the benefits should outweigh the costs for some individuals (i.e., the farmer) who perform the behavior even when alone. Second, once one individual is performing the behavior, the costs for others (i.e., the neighbor) are sufficiently reduced so that they are outweighed by the benefits. </p><p>David Wheatcroft and Trevor Price asked if this idea can explain cooperative behaviors in nature. They studied responses of small birds to various enemies over four years in the western Himalayas. Crows prey upon the eggs and chicks of small birds, and cuckoos parasitize their nests. Wheatcroft and Price used taxidermied mounts of crows and cuckoos to show that, when acting alone, the only individuals to strongly attack the mounts were those with nests nearby. As long as nest owners are present, birds without nearby nests also join. By contrast, hawk and owl mounts are always vigorously attacked. Wheatcroft and Price then developed a theory of changing cost:benefit relationships, assuming the principles outlined above apply. They show that the results are as expected if crows and cuckoos are not too costly to attack and costs decline with the number of birds attacking the mount, but benefits always accrue to individuals attacking hawks and owls. Simple mechanisms (i.e., join if you benefit) may regularly explain the formation of cooperative 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;">E</span>xplaining why individuals participate in risky group behaviors has been a long-term challenge. We experimentally studied the formation of groups of birds (“mobs”) that aggressively confront predators and avian nest parasites and developed a theoretical model to evaluate the conditions under which mobs arise. We presented taxidermied mounts of predators on adult birds (hawks and owls) and of nest threats (crows and cuckoos) at different distances to nests of <i>Phylloscopus</i> warblers. Even when alone, birds are aggressive towards predators of adult birds, both at and away from their nests. By contrast, birds aggressively confront nest threats alone only when they have a nest nearby. However, strong initial responses by nest owners lead individuals without nearby nests to increase their responses, thereby generating a mob. Building on these findings, we derive the conditions when individuals are incentivized to invest more when joining a high-gain individual compared to when acting alone. Strong responses of high-gain individuals acting alone tend to reduce the investments of other high-gain individuals that subsequently join. However, individuals that benefit sufficiently little from acting alone increase their investments when joining a high-gain individual and can even be sufficiently incentivized to join in when they would otherwise not act alone. Together, these results suggest an important role for key individuals in the generation of some group behaviors. </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, 05 Jun 2018 05:00:00 GMT “Gene-culture co-inheritance of a behavioral trait” http://amnat.org/an/newpapers/SepAguilar-A.html The DOI will be https://dx.doi.org/10.1086/698872 Gene-Culture Price equation shows when cultural selection beats genetic selection Abstract Many physical and behavioral traits in animals, including humans, are inherited both genetically and culturally. The presence of different inheritance systems affecting the same trait can result in complex evolutionary dynamics. Here, we present a general model that elucidates the distinct roles of cultural and genetic inheritance systems, and their interaction, in driving the evolution of complex phenotypes. In particular, we derive a Price equation that incorporates both cultural and genetic inheritance of a phenotype where the effects of genes and culture are additive. We then use this equation to investigate whether a genetically maladaptive phenotype can evolve under dual transmission. We examine the special case of altruism using an illustrative model, and show that cultural selection can overcome genetic selection when the variance in culture is sufficiently high with respect to genes. We also show that the presence of cultural transmission can modify genetic selection itself, making genetic selection more favorable to a trait than under purely genetic inheritance. Lastly, we consider the effect of different timescales of genetic and cultural transmission. We discuss the implications of our results for understanding the evolution of important co-inherited behaviors, including how our framework can be used to generate quantitative estimates of selection pressures required for a genetically maladaptive trait to evolve. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698872 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698872">Read the Article</a></i> </p> --> <p><b>Gene-Culture Price equation shows when cultural selection beats genetic selection </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;">M</span>any physical and behavioral traits in animals, including humans, are inherited both genetically and culturally. The presence of different inheritance systems affecting the same trait can result in complex evolutionary dynamics. Here, we present a general model that elucidates the distinct roles of cultural and genetic inheritance systems, and their interaction, in driving the evolution of complex phenotypes. In particular, we derive a Price equation that incorporates both cultural and genetic inheritance of a phenotype where the effects of genes and culture are additive. We then use this equation to investigate whether a genetically maladaptive phenotype can evolve under dual transmission. We examine the special case of altruism using an illustrative model, and show that cultural selection can overcome genetic selection when the variance in culture is sufficiently high with respect to genes. We also show that the presence of cultural transmission can modify genetic selection itself, making genetic selection more favorable to a trait than under purely genetic inheritance. Lastly, we consider the effect of different timescales of genetic and cultural transmission. We discuss the implications of our results for understanding the evolution of important co-inherited behaviors, including how our framework can be used to generate quantitative estimates of selection pressures required for a genetically maladaptive trait to evolve. </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, 05 Jun 2018 05:00:00 GMT “Fitness consequences of interspecific nesting associations among cavity nesting birds” http://amnat.org/an/newpapers/SepMouton.html The DOI will be https://dx.doi.org/10.1086/698873 Nest tree availability and nest predation risk affect the benefits and rate of nest tree sharing in cavity nesting birds Some of the most visually striking and exciting sights in nature are large herds, flocks, schools, and colonies of animals. Animals may benefit from being in a group with other species because it can reduce their chances of being killed by a predator, but on the other hand, large groups can attract predators. Competition over resources (i.e. food or breeding sites) between similar species can also cause fighting within the group making it difficult for groups to form. This suggests that similar species that often fight should keep their distance and not form groups. However, birds that nest in holes in trees (cavity nesters) are well known for aggressively attacking one another, especially around nests, can be seen sometimes nesting together in the same tree. How commonly does this occur? Why do they share nest trees in the first place? James Mouton and Tom Martin set out to answer these questions by looking at whether the number of nests sharing trees changed in years with different availability of nest sites and risk that a predator eats the eggs or offspring). They found that sharing nest trees was more common in years with more nest trees and in years with higher risk of nest predation. They also found that nests in shared trees were less likely to be depredated than solitary nests, but only in years with high risk of predation. Together, these findings suggest that birds may fight less when nest sites are abundant, allowing them to nest close together more often and that birds may nest close together even when then fight if predation risk is especially high. Still, experiments are needed to fully understand these patterns. Ultimately, it seems that even though they are known for fighting, cavity nesting birds tolerate nesting together in the right conditions. Abstract Interspecific aggregations of prey may provide benefits by mitigating predation risk, but they can also create costs if they increase competition for resources or are more easily detectable by predators. Variation in predation risk and resource availability may influence the occurrence and fitness effects of aggregating in nature. Yet, tests of such possibilities are lacking. Cavity nesting birds provide an interesting test case. They compete aggressively for resources and experience low nest predation rates, which might predict dispersion, but we found they commonly aggregate by sharing nest trees across 19 years of study. Tree sharing was more common when aspen were more abundant and somewhat more common in years with higher nest predation risk. Nest success was higher in shared trees when nest predation risk was higher than average. Ultimately, the costs and benefits of aggregating (nest tree sharing) varied across years and we outline hypotheses for future studies. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698873 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698873">Read the Article</a></i> </p> --> <p><b>Nest tree availability and nest predation risk affect the benefits and rate of nest tree sharing in cavity nesting birds </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>ome of the most visually striking and exciting sights in nature are large herds, flocks, schools, and colonies of animals. Animals may benefit from being in a group with other species because it can reduce their chances of being killed by a predator, but on the other hand, large groups can attract predators. Competition over resources (i.e. food or breeding sites) between similar species can also cause fighting within the group making it difficult for groups to form. This suggests that similar species that often fight should keep their distance and not form groups. However, birds that nest in holes in trees (cavity nesters) are well known for aggressively attacking one another, especially around nests, can be seen sometimes nesting together in the same tree. How commonly does this occur? Why do they share nest trees in the first place? </p><p>James Mouton and Tom Martin set out to answer these questions by looking at whether the number of nests sharing trees changed in years with different availability of nest sites and risk that a predator eats the eggs or offspring). They found that sharing nest trees was more common in years with more nest trees and in years with higher risk of nest predation. They also found that nests in shared trees were less likely to be depredated than solitary nests, but only in years with high risk of predation. Together, these findings suggest that birds may fight less when nest sites are abundant, allowing them to nest close together more often and that birds may nest close together even when then fight if predation risk is especially high. Still, experiments are needed to fully understand these patterns. Ultimately, it seems that even though they are known for fighting, cavity nesting birds tolerate nesting together in the right 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;">I</span>nterspecific aggregations of prey may provide benefits by mitigating predation risk, but they can also create costs if they increase competition for resources or are more easily detectable by predators. Variation in predation risk and resource availability may influence the occurrence and fitness effects of aggregating in nature. Yet, tests of such possibilities are lacking. Cavity nesting birds provide an interesting test case. They compete aggressively for resources and experience low nest predation rates, which might predict dispersion, but we found they commonly aggregate by sharing nest trees across 19 years of study. Tree sharing was more common when aspen were more abundant and somewhat more common in years with higher nest predation risk. Nest success was higher in shared trees when nest predation risk was higher than average. Ultimately, the costs and benefits of aggregating (nest tree sharing) varied across years and we outline hypotheses for future studies. </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, 05 Jun 2018 05:00:00 GMT “Female life history trade-offs and the maintenance of genetic variation in Drosophila melanogaster” http://amnat.org/an/newpapers/OctArbuthnott.html The DOI will be https://dx.doi.org/10.1086/698727 Many processes and trade-offs work together to weaken selection, allowing populations to maintain genetic diversity Why do we see so much variation within species, with individuals differing widely in traits that affect fitness? Natural and sexual selection should favour advantageous traits, and populations should become more homogeneous as selection increases the frequency of these traits. Yet substantial variation is observed in fitness-related traits in a wide variety of species. In this study, Arbuthnott tests a number of alternate hypotheses as to how variation is maintained using inbred lines of fruit flies. From dozens of trait measurements and experiments, the author finds that no one mechanism is strong enough to counteract selection and maintain variation on its own. However, the author finds a number of weak genetic correlations and trade-offs between different fitness-related traits, and suggests that several mechanisms may each weaken selection incrementally. When these weakening mechanisms are combined, they may act to slow the purging of disadvantageous traits, and maintain genetic variation within populations. This comprehensive study is the first to suggest that many weak processes may act together to maintain variation, which may have important implications for our understanding of genetic diversity and evolution. Abstract Why do we observe substantial variation in fitness-related traits under strong natural or sexual selection? While there is support for several selective and neutral mechanisms acting in select systems, we lack a comprehensive analysis of the relative importance of various mechanisms within a single system. Furthermore, while sexually selected male traits have been a central focus of this paradox, female sexual traits have rarely been considered. In this study, I evaluate the contribution of various selective mechanisms towards the maintenance of substantial variation in female attractiveness and offspring production observed among Drosophila melanogaster genotypes. I tested for contributions from antagonistic pleiotropy, frequency-dependent selection, changing environments, and sexual conflict. I found negative genetic correlations between some traits (male attractiveness vs. female resistance to male harm, early offspring production and reproductive senescence), and genotype-specific changes in fitness between environments. However, no measurement found strong trade-offs among the fitness components of these genotypes. Overall, I find little evidence that any one mechanism is strong enough to maintain genetic variation on its own. Instead, I suggest that many mechanisms may weaken the selection among genotypes, which would collectively allow neutral processes such as mutation-selection balance to maintain genetic variation within populations. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698727 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698727">Read the Article</a></i> </p> --> <p><b>Many processes and trade-offs work together to weaken selection, allowing populations to maintain genetic diversity </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;">W</span>hy do we see so much variation within species, with individuals differing widely in traits that affect fitness? Natural and sexual selection should favour advantageous traits, and populations should become more homogeneous as selection increases the frequency of these traits. Yet substantial variation is observed in fitness-related traits in a wide variety of species. In this study, Arbuthnott tests a number of alternate hypotheses as to how variation is maintained using inbred lines of fruit flies. From dozens of trait measurements and experiments, the author finds that no one mechanism is strong enough to counteract selection and maintain variation on its own. However, the author finds a number of weak genetic correlations and trade-offs between different fitness-related traits, and suggests that several mechanisms may each weaken selection incrementally. When these weakening mechanisms are combined, they may act to slow the purging of disadvantageous traits, and maintain genetic variation within populations. This comprehensive study is the first to suggest that many weak processes may act together to maintain variation, which may have important implications for our understanding of genetic diversity and evolution.</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;">W</span>hy do we observe substantial variation in fitness-related traits under strong natural or sexual selection? While there is support for several selective and neutral mechanisms acting in select systems, we lack a comprehensive analysis of the relative importance of various mechanisms within a single system. Furthermore, while sexually selected male traits have been a central focus of this paradox, female sexual traits have rarely been considered. In this study, I evaluate the contribution of various selective mechanisms towards the maintenance of substantial variation in female attractiveness and offspring production observed among <i>Drosophila melanogaster</i> genotypes. I tested for contributions from antagonistic pleiotropy, frequency-dependent selection, changing environments, and sexual conflict. I found negative genetic correlations between some traits (male attractiveness vs. female resistance to male harm, early offspring production and reproductive senescence), and genotype-specific changes in fitness between environments. However, no measurement found strong trade-offs among the fitness components of these genotypes. Overall, I find little evidence that any one mechanism is strong enough to maintain genetic variation on its own. Instead, I suggest that many mechanisms may weaken the selection among genotypes, which would collectively allow neutral processes such as mutation-selection balance to maintain genetic variation within populations.</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, 30 May 2018 05:00:00 GMT “Prey limitation drives variation in allometric scaling of predator-prey interactions” http://amnat.org/an/newpapers/OctCostaP.html The DOI will be https://dx.doi.org/10.1086/698726 Variation in allometric scaling of predator-prey interactions is predicted by gradients of prey limitation Predators should carefully choose their prey. Small-sized prey may be tricky to find and capture, and usually have low energetic return. In turn, too large prey are difficult to overcome, subdue, and even ingest. Therefore, foraging theories predict an intermediate optimal relative size-difference between predators and their prey. Although this theoretical concept has been widely used to model the dynamics and structure of predator-prey populations and food webs, empirical systems show a tremendous variation in predator-prey size ratios. To investigate the underlying causes of this unexpected variation, the authors analyzed more than 6,000 trophic interactions between tropical frog species and their prey across a diverse range of communities in the Pantanal wetlands of Brazil. Surprisingly, they demonstrated that variation in the relative size of predators and their prey is not simply “noise” but instead can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. Importantly, this study shows for the first time that the variance of size-scaling ratios is neither negligible nor constant as currently assumed, but instead it changes predictably across communities. This variation has important consequences for ecological and evolutionary dynamics of food webs. Together, these findings make clear that prey limitation leads to deviations from the universal size-scaling constant and thus challenges current paradigms of metabolic and food web theories. Abstract Ecologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, Predator-Prey Size Ratios (PPSR) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here, we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. We analyzed >6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size-dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.A limitação de presas explica a variação na alometria de interações predador-presa Ecólogos têm buscado há muito tempo uma constante alométrica universal que governe relações tróficas. Embora esse seja um conceito teórico atraente, razões de tamanho predador-presa (PPSR) variam amplamente entre e dentro de teias tróficas naturais, o que indica que predadores desviam de seus tamanhos ótimos de presa consumindo recursos relativamente maiores ou menores. Aqui, nós sugerimos que essa inesperada variação alométrica em interações tróficas pode ser predita por gradientes de limitação de presas, o que seria consistente com a Teoria do Forrageamento Ótimo. Nós analisamos >6.000 interações tróficas em 52 populações de quatro espécies de rãs tropicais ao longo de um gradiente de limitação de presas. A PPSR média e sua variância diferiram até duas ordens de magnitude entre e dentro das teias tróficas. Particularmente, conforme a disponibilidade de presas diminuiu nas teias tróficas, a PPSR e sua variância se tornaram mais dependentes do tamanho corpóreo dos predadores. Desse modo, interações tróficas não seguem uma constante alométrica fixa, mas variam previsivelmente de acordo com a magnitude da limitação de presas. Nossos resultados enfatizam a importância de diferentes contextos ecológicos no arranjo de teias tróficas e a necessidade de incorporar os mecanismos ecológicos que afetam a PPSR e sua variância em modelos de teias tróficas e comunidades. More forthcoming papers &raquo; <p><i>The DOI will be https://dx.doi.org/10.1086/698726 </i></p> <!-- <p><i><a href="https://dx.doi.org/10.1086/698726">Read the Article</a></i> </p> --> <p><b>Variation in allometric scaling of predator-prey interactions is predicted by gradients of prey limitation </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>redators should carefully choose their prey. Small-sized prey may be tricky to find and capture, and usually have low energetic return. In turn, too large prey are difficult to overcome, subdue, and even ingest. Therefore, foraging theories predict an intermediate optimal relative size-difference between predators and their prey. Although this theoretical concept has been widely used to model the dynamics and structure of predator-prey populations and food webs, empirical systems show a tremendous variation in predator-prey size ratios. </p><p>To investigate the underlying causes of this unexpected variation, the authors analyzed more than 6,000 trophic interactions between tropical frog species and their prey across a diverse range of communities in the Pantanal wetlands of Brazil. Surprisingly, they demonstrated that variation in the relative size of predators and their prey is not simply &ldquo;noise&rdquo; but instead can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. Importantly, this study shows for the first time that the variance of size-scaling ratios is neither negligible nor constant as currently assumed, but instead it changes predictably across communities. This variation has important consequences for ecological and evolutionary dynamics of food webs. Together, these findings make clear that prey limitation leads to deviations from the universal size-scaling constant and thus challenges current paradigms of metabolic and food web theories.</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;">E</span>cologists have long searched for a universal size-scaling constant that governs trophic interactions. Although this is an appealing theoretical concept, Predator-Prey Size Ratios (PPSR) vary strikingly across and within natural food webs, meaning that predators deviate from their optimal prey size by consuming relatively larger or smaller prey. Here, we suggest that this unexpected variation in allometric scaling of trophic interactions can be predicted by gradients of prey limitation consistent with predictions from Optimal Foraging Theory. We analyzed &gt;6,000 trophic interactions of 52 populations from four tropical frog species along a gradient of prey limitation. The mean of PPSR and its variance differed up to two orders of magnitude across and within food webs. Importantly, as prey availability decreased across food webs, PPSR and its variance became more size-dependent. Thus, trophic interactions did not follow a fixed allometric scaling but changed predictably with the strength of prey limitation. Our results emphasize the importance of ecological contexts in arranging food webs and the need to incorporate ecological drivers of PPSR and its variance in food web and community models.</p><h4>A limitação de presas explica a variação na alometria de interações predador-presa</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;">E</span>cólogos têm buscado há muito tempo uma constante alométrica universal que governe relações tróficas. Embora esse seja um conceito teórico atraente, razões de tamanho predador-presa (PPSR) variam amplamente entre e dentro de teias tróficas naturais, o que indica que predadores desviam de seus tamanhos ótimos de presa consumindo recursos relativamente maiores ou menores. Aqui, nós sugerimos que essa inesperada variação alométrica em interações tróficas pode ser predita por gradientes de limitação de presas, o que seria consistente com a Teoria do Forrageamento Ótimo. Nós analisamos >6.000 interações tróficas em 52 populações de quatro espécies de rãs tropicais ao longo de um gradiente de limitação de presas. A PPSR média e sua variância diferiram até duas ordens de magnitude entre e dentro das teias tróficas. Particularmente, conforme a disponibilidade de presas diminuiu nas teias tróficas, a PPSR e sua variância se tornaram mais dependentes do tamanho corpóreo dos predadores. Desse modo, interações tróficas não seguem uma constante alométrica fixa, mas variam previsivelmente de acordo com a magnitude da limitação de presas. Nossos resultados enfatizam a importância de diferentes contextos ecológicos no arranjo de teias tróficas e a necessidade de incorporar os mecanismos ecológicos que afetam a PPSR e sua variância em modelos de teias tróficas e comunidades. </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, 23 May 2018 05:00:00 GMT