ASN RSS https://amnat.org/ Latest press releases and announcements from the ASN en-us Wed, 22 Jan 2020 06:00:00 GMT 60 “Dispersal increases the resilience of tropical savanna and forest distributions” https://amnat.org/an/newpapers/May-Goel.html Nikunj Goel, Vishwesha Guttal, Simon A. Levin, and A. Carla Staver (May 2020) Dispersal may allow recovery of tropical savanna and forest biomes, but it may be slow Read the Article (Just Accepted) Anthropogenic carbon emissions are changing the global climate at an unprecedented rate. Although it is well accepted that these climatic changes will result in large-scale biome shifts, it is unclear whether these shifts are reversible. Historically, biogeographers have argued that biomes match perfectly to their prevailing climate, such that biomes continuously track spatially shifting climatic envelopes. Based on this historical view, biome shifts should be reversible, provided climatic changes are reversed. However, recent theoretical and empirical advances suggest that, in tropical savanna and forest ecosystems, fires can maintain multiple biomes states in intermediate rainfall conditions (the bistable region). If the rainfall changes beyond this bistable region, tropical ecosystems will undergo large-scale irreversible biome shifts. “Both of these modeling frameworks, however, ignore the fact that savanna and forest interact spatially at their ecotone through seed dispersal, which may facilitate biome recovery as seen in many abandoned agricultural plots in tropical forests,” said the lead author Nikunj Goel, Master’s student at Yale University in Department of Ecology and Evolutionary Biology (now a Ph.D. candidate at The&nbsp;University of Texas at Austin). In a new paper in The&nbsp;American Naturalist, Nikunj and his collaborators from Yale University, Princeton University, and Indian Institute of Science present a spatially explicit reaction-diffusion model to examine the role of dispersal in determining distribution and recovery of tropical biomes. Their model suggests that the savanna-forest boundary is not only determined by climate but also by continental-scale source-sink dynamics that are mediated by the geometrical shape of rainfall contours. The researchers find this non-intuitive prediction is consistent with biome patterns in sub-Saharan Africa. Intriguingly, the diffusion models predict that biome shifts due to global change might be reversible unless the remnant biome patches are too small. Abstract Global change may induce changes in savanna and forest distributions, but the dynamics of these changes remain unclear. Classical biome theory suggests that climate is predictive of biome distributions, such that shifts will be continuous and reversible. This view, however, cannot explain the overlap in the climatic ranges of tropical biomes, which some argue may result from fire-vegetation feedbacks, maintaining savanna and forest as bistable states. Under this view, biome shifts are argued to be discontinuous and irreversible. Mean-field bistable models, however, too, are limited as they cannot reproduce the spatial aggregation of biomes. Here, we suggest that both models ignore spatial processes, such as dispersal, which may be important when savanna and forest abut. We examine the contributions of dispersal to determining biome distributions using a 2D reaction-diffusion model, comparing results qualitatively to empirical savanna and forest distributions in sub-Saharan Africa. We find that the diffusion model resolves both the aforementioned limitations of biome models. First, local dispersive spatial interactions, with an underlying precipitation gradient, can reproduce the spatial aggregation of biomes with a stable savanna-forest boundary. Second, the boundary is not only determined by the amount of precipitation but also by the geometrical shape of the precipitation contours. These geometrical effects arise from continental-scale source-sink dynamics, which reproduces the mismatch between biome and climate. Dynamically, the spatial model predicts that dispersal may increase the resilience of tropical biome in response to global change: the boundary continuously tracks climate, recovering following disturbances, unless the remnant biome patches are too small. More forthcoming papers &raquo; <p>Nikunj Goel, Vishwesha Guttal, Simon A. Levin, and A. Carla Staver (May 2020) </p> <p><b>Dispersal may allow recovery of tropical savanna and forest biomes, but it may be slow </b></p> <p><i><a href="https://dx.doi.org/10.1086/708270">Read the Article</a></i> (Just Accepted) </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>nthropogenic carbon emissions are changing the global climate at an unprecedented rate. Although it is well accepted that these climatic changes will result in large-scale biome shifts, it is unclear whether these shifts are reversible. Historically, biogeographers have argued that biomes match perfectly to their prevailing climate, such that biomes continuously track spatially shifting climatic envelopes. Based on this historical view, biome shifts should be reversible, provided climatic changes are reversed. However, recent theoretical and empirical advances suggest that, in tropical savanna and forest ecosystems, fires can maintain multiple biomes states in intermediate rainfall conditions (the bistable region). If the rainfall changes beyond this bistable region, tropical ecosystems will undergo large-scale irreversible biome shifts. “Both of these modeling frameworks, however, ignore the fact that savanna and forest interact spatially at their ecotone through seed dispersal, which may facilitate biome recovery as seen in many abandoned agricultural plots in tropical forests,” said the lead author Nikunj Goel, Master’s student at Yale University in Department of Ecology and Evolutionary Biology (now a Ph.D. candidate at The&nbsp;University of Texas at Austin). </p><p>In a new paper in <i>The&nbsp;American Naturalist</i>, Nikunj and his collaborators from Yale University, Princeton University, and Indian Institute of Science present a spatially explicit reaction-diffusion model to examine the role of dispersal in determining distribution and recovery of tropical biomes. Their model suggests that the savanna-forest boundary is not only determined by climate but also by continental-scale source-sink dynamics that are mediated by the geometrical shape of rainfall contours. The researchers find this non-intuitive prediction is consistent with biome patterns in sub-Saharan Africa. Intriguingly, the diffusion models predict that biome shifts due to global change might be reversible unless the remnant biome patches are too small. </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;">G</span>lobal change may induce changes in savanna and forest distributions, but the dynamics of these changes remain unclear. Classical biome theory suggests that climate is predictive of biome distributions, such that shifts will be continuous and reversible. This view, however, cannot explain the overlap in the climatic ranges of tropical biomes, which some argue may result from fire-vegetation feedbacks, maintaining savanna and forest as bistable states. Under this view, biome shifts are argued to be discontinuous and irreversible. Mean-field bistable models, however, too, are limited as they cannot reproduce the spatial aggregation of biomes. Here, we suggest that both models ignore spatial processes, such as dispersal, which may be important when savanna and forest abut. We examine the contributions of dispersal to determining biome distributions using a 2D reaction-diffusion model, comparing results qualitatively to empirical savanna and forest distributions in sub-Saharan Africa. We find that the diffusion model resolves both the aforementioned limitations of biome models. First, local dispersive spatial interactions, with an underlying precipitation gradient, can reproduce the spatial aggregation of biomes with a stable savanna-forest boundary. Second, the boundary is not only determined by the amount of precipitation but also by the geometrical shape of the precipitation contours. These geometrical effects arise from continental-scale source-sink dynamics, which reproduces the mismatch between biome and climate. Dynamically, the spatial model predicts that dispersal may increase the resilience of tropical biome in response to global change: the boundary continuously tracks climate, recovering following disturbances, unless the remnant biome patches are too small.</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, 22 Jan 2020 06:00:00 GMT “Why are there so many flowering plants? A multi-scale analysis of plant diversification” https://amnat.org/an/newpapers/June-Hernandez.html Tania Hernández-Hernández and John J. Wiens (June 2020) A new study helps explain the extraordinary richness of flowering plants (angiosperms) relative to other plant groups Read the Article (Just Accepted) For hundreds of years, researchers have tried to understand why most land plant species are flowering plants, or angiosperms. Roughly 90% of land plants are angiosperms, even though angiosperms are young relative to other major groups, such as mosses, ferns, and liverworts. More than 200 years ago, Darwin considered the cause of the rapid proliferation of angiosperm species to be an “abominable mystery.” A new study may have finally solved this mystery. Working at the University of Arizona, Tania Hern&aacute;ndez-Hern&aacute;ndez and John J. Wiens generated a massive dataset of 31 traits for all 678 families of land plants. They then analyzed which traits best explained why some groups proliferated rapidly (like angiosperms) whereas others did not (like mosses). In contrast to earlier studies, they included dozens of traits and compared angiosperms to other groups to understand their rapid proliferation, rather than comparing a few traits within angiosperms.They find that fertilization of plants by animals (e.g. insect pollination) was the most important trait for explaining the rapid radiation of angiosperms. This result suggests that flowers are they key trait that explains the incredible success of angiosperms.They also find that many other patterns of diversity across plants are explained largely by how widely distributed each group is (range size). Widely distributed families radiate more rapidly. This pattern helps explain why some plant families have been more successful than others, across plants and within angiosperms, ferns, mosses, and gymnosperms. Finally, the study shows how traits associated with interactions between species (like insects pollinating plants) can be important for explaining diversity patterns at very deep timescales, among clades that are hundreds of millions of years old. In contrast, large-scale geographic factors (like range size) are more important among younger clades. This pattern may apply to many other groups of organisms. Abstract The causes of the rapid diversification and extraordinary richness of flowering plants (angiosperms) relative to other plant clades is a long-standing mystery. Angiosperms are only one among 10 major land plant clades (phyla), but include ~90% of land plant species. However, most studies that have tried to identify which traits might explain the remarkable diversification of angiosperms have focused only on richness patterns within angiosperms, and tested only one or a few traits at a single hierarchical scale. Here, we assemble a database of 31 diverse traits among 678 families and analyze relationships between traits and diversification rates across all land plants at three hierarchical levels (phylum, order, family) using phylogenetic multiple regression. We find that most variation (~85%) in diversification rates among major clades (phyla) is explained by biotically mediated fertilization (e.g., insect pollination) and clade-level geographic-range size. Different sets of traits explain diversification at different hierarchical levels, with geographic-range size dominating among families. Surprisingly, we find that traits related to local-scale species interactions (i.e. biotic fertilization) are particularly important for explaining diversification patterns at the deepest timescales, whereas large-scale geographic factors (i.e. clade-level range size) are more important at shallower timescales. This dichotomy might apply broadly across organisms. More forthcoming papers &raquo; <p>Tania Hernández-Hernández and John J. Wiens (June 2020) </p> <p><b>A new study helps explain the extraordinary richness of flowering plants (angiosperms) relative to other plant groups </b></p> <p><i><a href="https://dx.doi.org/10.1086/708273">Read the Article</a></i> (Just Accepted) </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;">F</span>or hundreds of years, researchers have tried to understand why most land plant species are flowering plants, or angiosperms. Roughly 90% of land plants are angiosperms, even though angiosperms are young relative to other major groups, such as mosses, ferns, and liverworts. More than 200 years ago, Darwin considered the cause of the rapid proliferation of angiosperm species to be an &ldquo;abominable mystery.&rdquo;</p> <p>A new study may have finally solved this mystery. Working at the University of Arizona, Tania Hern&aacute;ndez-Hern&aacute;ndez and John J. Wiens generated a massive dataset of 31 traits for all 678 families of land plants. They then analyzed which traits best explained why some groups proliferated rapidly (like angiosperms) whereas others did not (like mosses). In contrast to earlier studies, they included dozens of traits and compared angiosperms to other groups to understand their rapid proliferation, rather than comparing a few traits within angiosperms.</p><p>They find that fertilization of plants by animals (e.g. insect pollination) was the most important trait for explaining the rapid radiation of angiosperms. This result suggests that flowers are they key trait that explains the incredible success of angiosperms.</p><p>They also find that many other patterns of diversity across plants are explained largely by how widely distributed each group is (range size). Widely distributed families radiate more rapidly. This pattern helps explain why some plant families have been more successful than others, across plants and within angiosperms, ferns, mosses, and gymnosperms. </p><p>Finally, the study shows how traits associated with interactions between species (like insects pollinating plants) can be important for explaining diversity patterns at very deep timescales, among clades that are hundreds of millions of years old. In contrast, large-scale geographic factors (like range size) are more important among younger clades. This pattern may apply to many other groups of organisms. </p> <hr /><h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">T</span>he causes of the rapid diversification and extraordinary richness of flowering plants (angiosperms) relative to other plant clades is a long-standing mystery. Angiosperms are only one among 10 major land plant clades (phyla), but include ~90% of land plant species. However, most studies that have tried to identify which traits might explain the remarkable diversification of angiosperms have focused only on richness patterns within angiosperms, and tested only one or a few traits at a single hierarchical scale. Here, we assemble a database of 31 diverse traits among 678 families and analyze relationships between traits and diversification rates across all land plants at three hierarchical levels (phylum, order, family) using phylogenetic multiple regression. We find that most variation (~85%) in diversification rates among major clades (phyla) is explained by biotically mediated fertilization (e.g., insect pollination) and clade-level geographic-range size. Different sets of traits explain diversification at different hierarchical levels, with geographic-range size dominating among families. Surprisingly, we find that traits related to local-scale species interactions (i.e. biotic fertilization) are particularly important for explaining diversification patterns at the deepest timescales, whereas large-scale geographic factors (i.e. clade-level range size) are more important at shallower timescales. This dichotomy might apply broadly across organisms.</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, 22 Jan 2020 06:00:00 GMT “Evolution of reproduction periods in seasonal environments” https://amnat.org/an/newpapers/June-Sun.html Zepeng Sun, Kalle Parvinen, Mikko Heino, Johan A. J. Metz, André M. de Roos, and Ulf Dieckmann (June 2020) The authors studied how individuals time their reproduction in response to environmental changes Read the Article (Just Accepted) Climate change is expected to drive shifts in phenology, or the timing of life history events. Of all the seasonal events affected by climate change, the timing of reproduction (or breeding) is thought to be the most important. When it comes to the negative impacts of climate change on the reproduction of species, a so-called "match-mismatch hypothesis" arises in our mind, stating that the changes in climate can result in a mismatch between the offspring's food requirements and the actual food availabilities and in turn reduce the recruitment success. Although lots of efforts have been made on this topic, it is still not well-known how populations adjust their reproduction schedules in order to cope with changing seasonal patterns in their environment. In this study, Sun and his colleagues developed a theoretical model and investigated how the patterns in seasonal environments alter the evolution of the reproduction periods of populations. Besides the starting time, the model also allows the duration of the reproduction period to evolve independently. The authors present not only qualitative but also quantitative effects of the environmental patterns on evolution by reporting a rich array of evolutionary outcomes. Overall, the strength in seasonality of the environment determines whether energy reserves by adults is advantageous: in significantly seasonal environments, individuals will attempt to store energy reserves for reproduction at a later time; otherwise, they will just reproduce when they can. Surprisingly, in the former case, adults may start reproduction even while their offspring are still experiencing starvation. Furthermore, the competition ability on resource consumption between adults and juveniles also affects the outcomes: the more superior adults are on resource consumption, the more energy reserves (by adults) are favorable, and thus seasonality in reproduction becomes more significant. Abstract Many species are subject to seasonal cycles in resource availability, affecting the timing of their reproduction. Using a stage-structured consumer-resource model in which juvenile development and maturation are resource-dependent, we study how a species’ reproductive schedule evolves dependent on the seasonality of its resource. We find three qualitatively different reproduction modes. First, continuous income breeding (with adults reproducing throughout the year) evolves in absence of significant seasonality. Second, seasonal income breeding (with adults reproducing unless they are starving) evolves when resource availability is sufficiently seasonal and juveniles are more efficient resource foragers. Third, seasonal capital breeding (with adults reproducing partly through the use of energy reserves) evolves when resource availability is sufficiently seasonal and adults are more efficient resource foragers. Such capital breeders start reproduction already while their offspring are still experiencing starvation. Changes in seasonality lead to continuous transitions between continuous and seasonal income breeding, but the change between income and capital breeding involves a hysteresis pattern, such that a population’s evolutionarily stable reproduction pattern depends on its initial one. Taken together, our findings show how adaptation to seasonal environments can result in a rich array of outcomes, exhibiting seasonal or continuous reproduction, with or without energy reserves. More forthcoming papers &raquo; <p>Zepeng Sun, Kalle Parvinen, Mikko Heino, Johan A. J. Metz, André M. de Roos, and Ulf Dieckmann (June 2020) </p> <p><b>The authors studied how individuals time their reproduction in response to environmental changes </b></p> <p><i><a href="https://dx.doi.org/10.1086/708274">Read the Article</a></i> (Just Accepted) </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;">C</span>limate change is expected to drive shifts in phenology, or the timing of life history events. Of all the seasonal events affected by climate change, the timing of reproduction (or breeding) is thought to be the most important. When it comes to the negative impacts of climate change on the reproduction of species, a so-called "match-mismatch hypothesis" arises in our mind, stating that the changes in climate can result in a mismatch between the offspring's food requirements and the actual food availabilities and in turn reduce the recruitment success. Although lots of efforts have been made on this topic, it is still not well-known how populations adjust their reproduction schedules in order to cope with changing seasonal patterns in their environment. </p> <p>In this study, Sun and his colleagues developed a theoretical model and investigated how the patterns in seasonal environments alter the evolution of the reproduction periods of populations. Besides the starting time, the model also allows the duration of the reproduction period to evolve independently. The authors present not only qualitative but also quantitative effects of the environmental patterns on evolution by reporting a rich array of evolutionary outcomes. Overall, the strength in seasonality of the environment determines whether energy reserves by adults is advantageous: in significantly seasonal environments, individuals will attempt to store energy reserves for reproduction at a later time; otherwise, they will just reproduce when they can. Surprisingly, in the former case, adults may start reproduction even while their offspring are still experiencing starvation. Furthermore, the competition ability on resource consumption between adults and juveniles also affects the outcomes: the more superior adults are on resource consumption, the more energy reserves (by adults) are favorable, and thus seasonality in reproduction becomes more significant. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>any species are subject to seasonal cycles in resource availability, affecting the timing of their reproduction. Using a stage-structured consumer-resource model in which juvenile development and maturation are resource-dependent, we study how a species’ reproductive schedule evolves dependent on the seasonality of its resource. We find three qualitatively different reproduction modes. First, continuous income breeding (with adults reproducing throughout the year) evolves in absence of significant seasonality. Second, seasonal income breeding (with adults reproducing unless they are starving) evolves when resource availability is sufficiently seasonal and juveniles are more efficient resource foragers. Third, seasonal capital breeding (with adults reproducing partly through the use of energy reserves) evolves when resource availability is sufficiently seasonal and adults are more efficient resource foragers. Such capital breeders start reproduction already while their offspring are still experiencing starvation. Changes in seasonality lead to continuous transitions between continuous and seasonal income breeding, but the change between income and capital breeding involves a hysteresis pattern, such that a population’s evolutionarily stable reproduction pattern depends on its initial one. Taken together, our findings show how adaptation to seasonal environments can result in a rich array of outcomes, exhibiting seasonal or continuous reproduction, with or without energy reserves. </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, 22 Jan 2020 06:00:00 GMT “Individual specialization and multi-host epidemics: Disease spread in plant-pollinator networks” https://amnat.org/an/newpapers/May-Ellner.html Stephen P. Ellner, Wee Hao Ng, and Christopher R. Myers (May 2020) Disease outbreaks can be greatly facilitated by within-species variation in habitat or diet preferences of hosts Read the Article (Just Accepted) When you’ve gazed at a patch of flowers, perhaps you’ve been mesmerized by the bees moving from flower to flower, collecting nectar and pollen. Maybe you know enough about bees to recognize bumble bees, honey bees and a few other common species. Much of what we know about insect and other animals’ behavior is based on observations that distinguish between different species, but assume that all individuals in a species behave similarly. It would be as if aliens visiting Earth conclude that every human roots for both the Yankees and the Red Sox, based on the aggregate behavior of humans in the northeast US. But like humans with narrow sports-team allegiances, many individual bees (and other animals) have much narrower feeding preferences than their species as a whole, with individual preferences changing over time. The authors of this paper are part of a multi-university study of disease spread in communities with dozens of bee and flower species. Many bee diseases are spread by infected bees depositing pathogens on flowers, which can infect other bees visiting those flowers. The authors develop predictive models for forecasting and control of bee diseases. In this paper, they asked how disease spread is impacted by the narrow preferences of individual bees. Adding this feature to their previous model, they discovered that if bees stick to their preferences for a sufficiently long time before switching, this can have an enormous impact on whether a disease can persist. A disease predicted to die out if all bees are assumed to behave the same could actually be very strongly persistent due to particular bee-flower subnetworks that maintain infection. The overall prevalence of a disease in a multi-host community, in contrast, can either increase or decrease due to among-bee variability, depending on the details of the foraging network. Abstract Many parasites infect multiple species, and persist through a combination of within- and between-species transmission. Multispecies transmission networks are typically constructed at the species level, linking two species if any individuals of those species interact. However, generalist species often consist of specialized individuals that prefer different subsets of available resources, so individual- and species-level contact networks can differ systematically. To explore the epidemiological impacts of host specialization, we build and study a model for pollinator pathogens on plant-pollinator networks, in which individual pollinators have dynamic preferences for different flower species. We find that modeling and analysis ignoring individual host specialization can predict die-off of a disease that actually is strongly persistent, and can badly over- or under-predict steady-state disease prevalence. Effects of individual preferences remain substantial whenever mean preference duration exceeds half the mean time from infection to recovery or death. Similar results hold in a model where hosts foraging in different habitats have different frequencies of contact with an environmental reservoir for the pathogen. Thus, even if all hosts have the same long-run average behavior, dynamic individual differences can profoundly affect disease persistence and prevalence. More forthcoming papers &raquo; <p>Stephen P. Ellner, Wee Hao Ng, and Christopher R. Myers (May 2020) </p> <p><b>Disease outbreaks can be greatly facilitated by within-species variation in habitat or diet preferences of hosts </b></p> <p><i><a href="https://dx.doi.org/10.1086/708272">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>hen you’ve gazed at a patch of flowers, perhaps you’ve been mesmerized by the bees moving from flower to flower, collecting nectar and pollen. Maybe you know enough about bees to recognize bumble bees, honey bees and a few other common species. Much of what we know about insect and other animals’ behavior is based on observations that distinguish between different species, but assume that all individuals in a species behave similarly. It would be as if aliens visiting Earth conclude that every human roots for both the Yankees and the Red Sox, based on the aggregate behavior of humans in the northeast US. But like humans with narrow sports-team allegiances, many individual bees (and other animals) have much narrower feeding preferences than their species as a whole, with individual preferences changing over time. </p> <p>The authors of this paper are part of a multi-university study of disease spread in communities with dozens of bee and flower species. Many bee diseases are spread by infected bees depositing pathogens on flowers, which can infect other bees visiting those flowers. The authors develop predictive models for forecasting and control of bee diseases. In this paper, they asked how disease spread is impacted by the narrow preferences of individual bees. Adding this feature to their previous model, they discovered that if bees stick to their preferences for a sufficiently long time before switching, this can have an enormous impact on whether a disease can persist. A disease predicted to die out if all bees are assumed to behave the same could actually be very strongly persistent due to particular bee-flower subnetworks that maintain infection. The overall prevalence of a disease in a multi-host community, in contrast, can either increase or decrease due to among-bee variability, depending on the details of the foraging network. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>any parasites infect multiple species, and persist through a combination of within- and between-species transmission. Multispecies transmission networks are typically constructed at the species level, linking two species if any individuals of those species interact. However, generalist species often consist of specialized individuals that prefer different subsets of available resources, so individual- and species-level contact networks can differ systematically. To explore the epidemiological impacts of host specialization, we build and study a model for pollinator pathogens on plant-pollinator networks, in which individual pollinators have dynamic preferences for different flower species. We find that modeling and analysis ignoring individual host specialization can predict die-off of a disease that actually is strongly persistent, and can badly over- or under-predict steady-state disease prevalence. Effects of individual preferences remain substantial whenever mean preference duration exceeds half the mean time from infection to recovery or death. Similar results hold in a model where hosts foraging in different habitats have different frequencies of contact with an environmental reservoir for the pathogen. Thus, even if all hosts have the same long-run average behavior, dynamic individual differences can profoundly affect disease persistence and prevalence. </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, 22 Jan 2020 06:00:00 GMT “Parental age effects and the evolution of senescence” https://amnat.org/an/newpapers/May-Barks.html Patrick M. Barks and Robert A. Laird (May 2020) Parental age effects on offspring quality modify predictions from classic evolutionary theory on senescence Read the Article (Just Accepted) Across the tree of life, individuals of many species are subject to age-related deterioration, colloquially known as ‘ageing’. At the extreme end of the ageing spectrum are organisms like Pacific salmon, mayflies, and certain species of bamboo, which rapidly deteriorate and die following a single bout of reproduction. At the opposite end are organisms whose rates of survival and reproduction remain stable or even increase throughout adulthood, like certain types of molluscs, tortoises and coniferous trees. While there exists a great deal of evolutionary theory to explain why ageing might evolve in the first place, evolutionary biologists have a limited understanding of the factors that shape variation in rates of ageing, both within and among species. Researchers Patrick Barks and Robert Laird, working at the University of Lethbridge in Alberta, Canada, developed a mathematical model to investigate how rates of ageing may be shaped by a phenomenon known as a ‘parental age effect’, which occurs when offspring fitness consistently changes with parental age. For example, in some species, parents may gain experience or better territories as they age, leading to increases in offspring fitness with parental age. In other species, like members of the aquatic plant family known as duckweeds, parental ‘fronds’ tend to produce smaller, less-fecund offspring as they age. By analyzing models with both real and simulated data, Barks and Laird showed that, for organisms like duckweed in which offspring fitness tends to decline with parental age, natural selection favours stronger age-related declines in parental survival and reproduction (i.e. faster ageing) than would otherwise be expected. Conversely, age-related increases in offspring quality can diminish the strength of selection for age-related deterioration. Abstract Most theory on the evolution of senescence implicitly assumes that all offspring are of equal quality. However, in addition to age-related declines in survival and fecundity (classically-defined senescence), many organisms exhibit age-related declines in offspring quality, a phenomenon known as a parental age effect. Theoretical work suggests that parental age effects may alter age-trajectories of selection and therefore shape the evolution of senescence; however, to date, these analyses have been limited to idealized life cycles, and models of maternal care in human populations. To gain a broader understanding of how parental age effects may shape age-trajectories of selection, we extend the classic age-structured population projection model to also account for parental age structure, and apply this model to empirical data from an aquatic plant known to exhibit parental age effects (the duckweed Lemna minor), as well as a diverse set of simulated life cycles. Our results suggest that parental age effects alter predictions from classic theory on the evolution of senescence. Age-related declines in offspring quality reduce the relative value of late-life reproduction, leading to steeper age-related declines in the force of natural selection than would otherwise be expected, and potentially favoring the evolution of more rapid rates of senescence. More forthcoming papers &raquo; <p>Patrick M. Barks and Robert A. Laird (May 2020) </p> <p><b>Parental age effects on offspring quality modify predictions from classic evolutionary theory on senescence </b></p> <p><i><a href="https://dx.doi.org/10.1086/708271">Read the Article</a></i> (Just Accepted) </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>cross the tree of life, individuals of many species are subject to age-related deterioration, colloquially known as ‘ageing’. At the extreme end of the ageing spectrum are organisms like Pacific salmon, mayflies, and certain species of bamboo, which rapidly deteriorate and die following a single bout of reproduction. At the opposite end are organisms whose rates of survival and reproduction remain stable or even increase throughout adulthood, like certain types of molluscs, tortoises and coniferous trees. While there exists a great deal of evolutionary theory to explain why ageing might evolve in the first place, evolutionary biologists have a limited understanding of the factors that shape variation in rates of ageing, both within and among species. </p><p>Researchers Patrick Barks and Robert Laird, working at the University of Lethbridge in Alberta, Canada, developed a mathematical model to investigate how rates of ageing may be shaped by a phenomenon known as a ‘parental age effect’, which occurs when offspring fitness consistently changes with parental age. For example, in some species, parents may gain experience or better territories as they age, leading to increases in offspring fitness with parental age. In other species, like members of the aquatic plant family known as duckweeds, parental ‘fronds’ tend to produce smaller, less-fecund offspring as they age. </p><p>By analyzing models with both real and simulated data, Barks and Laird showed that, for organisms like duckweed in which offspring fitness tends to decline with parental age, natural selection favours stronger age-related declines in parental survival and reproduction (i.e. faster ageing) than would otherwise be expected. Conversely, age-related increases in offspring quality can diminish the strength of selection for age-related deterioration. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>ost theory on the evolution of senescence implicitly assumes that all offspring are of equal quality. However, in addition to age-related declines in survival and fecundity (classically-defined senescence), many organisms exhibit age-related declines in offspring quality, a phenomenon known as a parental age effect. Theoretical work suggests that parental age effects may alter age-trajectories of selection and therefore shape the evolution of senescence; however, to date, these analyses have been limited to idealized life cycles, and models of maternal care in human populations. To gain a broader understanding of how parental age effects may shape age-trajectories of selection, we extend the classic age-structured population projection model to also account for parental age structure, and apply this model to empirical data from an aquatic plant known to exhibit parental age effects (the duckweed <i>Lemna minor</i>), as well as a diverse set of simulated life cycles. Our results suggest that parental age effects alter predictions from classic theory on the evolution of senescence. Age-related declines in offspring quality reduce the relative value of late-life reproduction, leading to steeper age-related declines in the force of natural selection than would otherwise be expected, and potentially favoring the evolution of more rapid rates of senescence. </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, 22 Jan 2020 06:00:00 GMT “Vertical transmission of a nematode from female lizards to the brains of their offspring” https://amnat.org/an/newpapers/May-Feiner.html Nathalie Feiner, Sueli de Souza-Lima, Fátima Jorge, Soraya Naem, Fabien Aubret, Tobias Uller, and Steven A. Nadler (May 2020) Nematodes have cracked a new code: first report of vertical transmission of a nematode through the amniote egg Read the Article (Just Accepted) Parasites are most inventive when it comes to exploiting new hosts. But this requires them to be transmitted from one host individual to another. One possible way is to simply infect the offspring of their current host. Thus far, such vertical transmission has never been shown in egg-laying birds or reptiles, suggesting that the amniote egg is an effective barrier against infection. A new discovery in the European wall lizard shows that this barrier can be broken. Feiner and colleagues show that an undescribed species of nematode has broken the defense system of the egg by infecting the embryo before the egg is shelled. Nematodes quickly enter the brain of the early embryo, where they can avoid being busted by the embryo’s immune system. Lizard eggs are only shelled once the embryo brain has started to form. This may explain why this nematode life style is possible in lizards, but not in turtles, crocodiles or birds. The eggs of the latter three groups are shelled when the embryo is very young, and therefore likely too small to be infected by macro-parasites. The nematode is closely related to gut-dwelling nematodes of lizards which gives us a clue about the origin of this new lifestyle. Among the adaptations that this nematode has evolved, its tiny body size that allows it to find its way into the lizard brain is the most obvious, but many more remain to be discovered. While this first report simply identifies the presence of vertical transmission, the authors hope that their finding will inspire more research that can establish how and why these nematodes evolved, and what impact they may have on their lizard hosts. Abstract Parasites have evolved a diversity of life styles that exploit the biology of their hosts. Some nematodes that parasitize mammals pass via the placenta or milk from one host to another. Similar cases of vertical transmission have never been reported in avian and non-avian reptiles, suggesting that egg laying may constrain the means of parasite transmission. However, here we report the first incidence of transovarial transmission of a previously undescribed nematode in an egg-laying amniote, the common wall lizard, Podarcis muralis. Nematodes enter the developing brain from the female ovary early in embryonic development. Infected lizard embryos develop normally and hatch with nematodes residing in their braincase. We present a morphological and molecular phylogenetic characterization of the nematode and suggest that particular features of lizard biology that are absent from birds and turtles facilitated the evolutionary origin of this novel life history. More forthcoming papers &raquo; <p>Nathalie Feiner, Sueli de Souza-Lima, Fátima Jorge, Soraya Naem, Fabien Aubret, Tobias Uller, and Steven A. Nadler (May 2020) </p> <p><b>Nematodes have cracked a new code: first report of vertical transmission of a nematode through the amniote egg </b></p> <p><i><a href="https://dx.doi.org/10.1086/708188">Read the Article</a></i> (Just Accepted) </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>arasites are most inventive when it comes to exploiting new hosts. But this requires them to be transmitted from one host individual to another. One possible way is to simply infect the offspring of their current host. Thus far, such vertical transmission has never been shown in egg-laying birds or reptiles, suggesting that the amniote egg is an effective barrier against infection. </p><p>A new discovery in the European wall lizard shows that this barrier can be broken. Feiner and colleagues show that an undescribed species of nematode has broken the defense system of the egg by infecting the embryo before the egg is shelled. Nematodes quickly enter the brain of the early embryo, where they can avoid being busted by the embryo’s immune system. </p><p>Lizard eggs are only shelled once the embryo brain has started to form. This may explain why this nematode life style is possible in lizards, but not in turtles, crocodiles or birds. The eggs of the latter three groups are shelled when the embryo is very young, and therefore likely too small to be infected by macro-parasites. </p><p>The nematode is closely related to gut-dwelling nematodes of lizards which gives us a clue about the origin of this new lifestyle. Among the adaptations that this nematode has evolved, its tiny body size that allows it to find its way into the lizard brain is the most obvious, but many more remain to be discovered. While this first report simply identifies the presence of vertical transmission, the authors hope that their finding will inspire more research that can establish how and why these nematodes evolved, and what impact they may have on their lizard hosts. </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>arasites have evolved a diversity of life styles that exploit the biology of their hosts. Some nematodes that parasitize mammals pass via the placenta or milk from one host to another. Similar cases of vertical transmission have never been reported in avian and non-avian reptiles, suggesting that egg laying may constrain the means of parasite transmission. However, here we report the first incidence of transovarial transmission of a previously undescribed nematode in an egg-laying amniote, the common wall lizard, <i>Podarcis muralis</i>. Nematodes enter the developing brain from the female ovary early in embryonic development. Infected lizard embryos develop normally and hatch with nematodes residing in their braincase. We present a morphological and molecular phylogenetic characterization of the nematode and suggest that particular features of lizard biology that are absent from birds and turtles facilitated the evolutionary origin of this novel life history.</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, 21 Jan 2020 06:00:00 GMT “How long does it take to fix a favorable mutation, and why should we care?” https://amnat.org/an/newpapers/May-Charlesworth.html Brian Charlesworth (May 2020) Read the Article (Just Accepted)Evolutionary change under natural selection often involves the spread of a beneficial mutation in a gene throughout a population, replacing the ancestral state of the gene. In order to understand how evolution works, it is important to know how long it takes for this process to occur. This question was investigated by mathematical modeling early in the twentieth century. The results showed that the time involved is usually a relatively small multiple of the effect of the mutation on fitness, which helped to convince biologists of the importance of natural selection. If it had turned out that a new mutation would take millions of generations to spread to a high frequency within a population from a very low starting frequency, there would be serious doubts about natural selection as a cause of evolution. But these results assumed that random fluctuations in the frequency of a mutation can be ignored, provided that the population size was large enough. When a mutation is either very rare or very common, however, such fluctations occur even in a very large population. Their effects can be determined by simple approximations, which yield formulae for both the mean and the amount of variability in the time taken for a mutation to spread through a population. While the classical results are still largely valid, the new findings have implications for contemporary work, in which researchers are trying to infer the action of selection from data on variation in DNA sequences among individuals within a species. Abstract The time taken for a selectively favorable allele to spread through a single population was investigated early in the history of population genetics. The resulting formulae are based on deterministic dynamics, leading to inaccuracies at allele frequencies close to zero or one. To remedy this problem, the properties of the stochastic phases at either endpoint of allele frequency need to be analysed. This paper uses a heuristic approach to determining the expected times spent in the stochastic and deterministic phases of allele frequency trajectories, for a model of weak selection at a single locus that is valid for inbreeding populations and for autosomal and sex-linked inheritance. The net fixation time is surprisingly insensitive to the level of dominance of a favorable mutation, even with random mating. Approximate expressions for the variance of the net fixation time are also obtained, which imply that there can be substantial stochastic effects even in very large populations. The accuracy of the approximations was evaluated by comparisons with computer simulations. The results reveal some areas that need further investigation, if a full understanding of selective sweeps is to be obtained, notably the possibility that fixations of slightly deleterious mutations may be affecting variability at closely linked sites. More forthcoming papers &raquo; <p>Brian Charlesworth (May 2020)</p> <p><i><a href="https://dx.doi.org/10.1086/708187">Read the Article</a></i> (Just Accepted)</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;">E</span>volutionary change under natural selection often involves the spread of a beneficial mutation in a gene throughout a population, replacing the ancestral state of the gene. In order to understand how evolution works, it is important to know how long it takes for this process to occur. This question was investigated by mathematical modeling early in the twentieth century. The results showed that the time involved is usually a relatively small multiple of the effect of the mutation on fitness, which helped to convince biologists of the importance of natural selection. If it had turned out that a new mutation would take millions of generations to spread to a high frequency within a population from a very low starting frequency, there would be serious doubts about natural selection as a cause of evolution.</p> <p>But these results assumed that random fluctuations in the frequency of a mutation can be ignored, provided that the population size was large enough. When a mutation is either very rare or very common, however, such fluctations occur even in a very large population. Their effects can be determined by simple approximations, which yield formulae for both the mean and the amount of variability in the time taken for a mutation to spread through a population. While the classical results are still largely valid, the new findings have implications for contemporary work, in which researchers are trying to infer the action of selection from data on variation in DNA sequences among individuals within a species.</p> <hr /> <h3>Abstract</h3> <p><span style="line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-size: 40px; font-weight: bold; float: left;">T</span>he time taken for a selectively favorable allele to spread through a single population was investigated early in the history of population genetics. The resulting formulae are based on deterministic dynamics, leading to inaccuracies at allele frequencies close to zero or one. To remedy this problem, the properties of the stochastic phases at either endpoint of allele frequency need to be analysed. This paper uses a heuristic approach to determining the expected times spent in the stochastic and deterministic phases of allele frequency trajectories, for a model of weak selection at a single locus that is valid for inbreeding populations and for autosomal and sex-linked inheritance. The net fixation time is surprisingly insensitive to the level of dominance of a favorable mutation, even with random mating. Approximate expressions for the variance of the net fixation time are also obtained, which imply that there can be substantial stochastic effects even in very large populations. The accuracy of the approximations was evaluated by comparisons with computer simulations. The results reveal some areas that need further investigation, if a full understanding of selective sweeps is to be obtained, notably the possibility that fixations of slightly deleterious mutations may be affecting variability at closely linked sites.</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, 21 Jan 2020 06:00:00 GMT “Ecological transitions in grouping benefits explain the paradox of environmental quality and sociality” https://amnat.org/an/newpapers/May-Liu-A.html Mark Liu (劉彥廷), Shih-Fan Chan (詹仕凡), Dustin R. Rubenstein, Syuan-Jyun Sun (孫烜駿), Bo-Fei Chen (陳伯飛), and Sheng-Feng Shen (沈聖峰) (May 2020) Sociality is favored under a wide range of environmental conditions Read the Article (Just Accepted) Abstract Both benign and harsh environments promote the evolution of sociality. This paradox—societies occur in environments of such contrasting quality—may be explained by the different types of benefits that individuals receive from grouping: resource defense benefits that derive from group-defended critical resources versus collective action benefits that result from social cooperation among group member. Here, we investigate cooperative behavior in the burying beetle Nicrophorus nepalensis along an elevational gradient where environmental quality (climate and competiton) varies with altitude. We show that climate (temperature) and competition (both intra- and interspecific) independently and synergistically influence sociality via different grouping benefits that vary along the gradient. At low elevations where interspecific competition for resources is intense, groups gain from the collective action benefit of increased interspecific competitive ability. In contrast, pairs have higher fitness at intermediate elevations where intraspecific competition for resources is greatest because resource defense is the key grouping benefit. However, groups and pairs have similar fitness at high elevations, suggesting that there is no grouping benefit in such physiologically challenging environments. Our results demonstrate that sociality is favored for different reasons under a range of environmental conditions, perhaps explaining why animal societies occur in environments of such contrasting quality. 合作利益隨著生境的轉換解釋在不同環境下社會行為演化的悖論 良性和惡劣環境都可能促進社會行為的演化,此一悖論或可透過個體從群體合作中獲得不同類型的合作利益來解釋。在良性環境中,高族群密度導致相對激烈的種內競爭,增加了排除種內競爭的成本。透過共享並共同防禦資源,可提高種內競爭的能力(資源防禦利益),故促進合作群體的形成。反之,在惡劣環境中,動物可以透過合作來克服環境挑戰或種間競爭,以獲得各種生存及繁殖上的利益(集體加成利益)。為了確定不同的合作利益能否解釋社會行為為何能在不同的環境條件下出現,我們研究了尼泊爾埋葬蟲(Nicrophorus nepalensis)的合作行為在台灣沿著海拔梯度的改變。我們的研究顯示,埋葬蟲群體在不同海拔受氣候(氣溫)和資源競爭(種內與種間)的單獨及協同影響,因而獲得不同類型的合作利益。在種間資源競爭強烈的低海拔地區,形成合作群體可獲得較高的集體加成利益,群體的人均生產率要高於單對個體。反之,在中海拔地區,由於有較強烈的種內資源競爭,形成群體可獲得較高的資源防禦利益,但單對個體的人均生產力卻高於群體。在高海拔地區,群體和單對個體人均生產率則相似,顯示埋葬蟲在這種生理狀況受到嚴峻挑戰的高海拔環境中並沒有群體優勢。我們的結果說明,在不同的環境條件下,生物的合作行為皆可能為其帶來優勢,這也許可以解釋為何動物社會可以在不同環境條件下形成的悖論。 More forthcoming papers &raquo; <p>Mark Liu (劉彥廷), Shih-Fan Chan (詹仕凡), Dustin R. Rubenstein, Syuan-Jyun Sun (孫烜駿), Bo-Fei Chen (陳伯飛), and Sheng-Feng Shen (沈聖峰) (May 2020) </p> <p><b>Sociality is favored under a wide range of environmental conditions </b></p> <p><i><a href="https://dx.doi.org/10.1086/708185">Read the Article</a></i> (Just Accepted) </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;">B</span>oth benign and harsh environments promote the evolution of sociality. This paradox&mdash;societies occur in environments of such contrasting quality&mdash;may be explained by the different types of benefits that individuals receive from grouping: resource defense benefits that derive from group-defended critical resources versus collective action benefits that result from social cooperation among group member. Here, we investigate cooperative behavior in the burying beetle <i>Nicrophorus nepalensis</i> along an elevational gradient where environmental quality (climate and competiton) varies with altitude. We show that climate (temperature) and competition (both intra- and interspecific) independently and synergistically influence sociality via different grouping benefits that vary along the gradient. At low elevations where interspecific competition for resources is intense, groups gain from the collective action benefit of increased interspecific competitive ability. In contrast, pairs have higher fitness at intermediate elevations where intraspecific competition for resources is greatest because resource defense is the key grouping benefit. However, groups and pairs have similar fitness at high elevations, suggesting that there is no grouping benefit in such physiologically challenging environments. Our results demonstrate that sociality is favored for different reasons under a range of environmental conditions, perhaps explaining why animal societies occur in environments of such contrasting quality.</p> <h4>合作利益隨著生境的轉換解釋在不同環境下社會行為演化的悖論</h4> <p>良性和惡劣環境都可能促進社會行為的演化,此一悖論或可透過個體從群體合作中獲得不同類型的合作利益來解釋。在良性環境中,高族群密度導致相對激烈的種內競爭,增加了排除種內競爭的成本。透過共享並共同防禦資源,可提高種內競爭的能力(資源防禦利益),故促進合作群體的形成。反之,在惡劣環境中,動物可以透過合作來克服環境挑戰或種間競爭,以獲得各種生存及繁殖上的利益(集體加成利益)。為了確定不同的合作利益能否解釋社會行為為何能在不同的環境條件下出現,我們研究了尼泊爾埋葬蟲(<i>Nicrophorus nepalensis</i>)的合作行為在台灣沿著海拔梯度的改變。我們的研究顯示,埋葬蟲群體在不同海拔受氣候(氣溫)和資源競爭(種內與種間)的單獨及協同影響,因而獲得不同類型的合作利益。在種間資源競爭強烈的低海拔地區,形成合作群體可獲得較高的集體加成利益,群體的人均生產率要高於單對個體。反之,在中海拔地區,由於有較強烈的種內資源競爭,形成群體可獲得較高的資源防禦利益,但單對個體的人均生產力卻高於群體。在高海拔地區,群體和單對個體人均生產率則相似,顯示埋葬蟲在這種生理狀況受到嚴峻挑戰的高海拔環境中並沒有群體優勢。我們的結果說明,在不同的環境條件下,生物的合作行為皆可能為其帶來優勢,這也許可以解釋為何動物社會可以在不同環境條件下形成的悖論。 </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, 21 Jan 2020 06:00:00 GMT “Age-related brood parasitism and egg rejection in magpie hosts” https://amnat.org/an/newpapers/May-Martinez.html Juan Gabriel Mart&iacute;nez, Mercedes Molina-Morales, Marta Precioso, and Jes&uacute;s Miguel Avil&eacute;s (May 2020) We show that individual hosts of a cuckoo species change the expression of their main defensive behaviour as they age Read the Article (Just Accepted)Breeding for some birds ends up in a disaster: instead of rearing their own healthy chicks, they take care of intruders, the cuckoos, which get rid of any legitimate offspring in the nest and monopolize all the care that host parents should be providing to their nestlings. But hosts of brood parasites are not always parasitized, and if they do, they may not be defenseless, since some individuals are able to recognize and reject cuckoo eggs. If natural selection favors individuals able to avoid parasitism, why do some individuals escape parasitism and/or are able to reject cuckoo eggs, whereas others become victims of the parasites? This article explores how considering the age of individual hosts may help to answer this. Researchers Juan Gabriel Martínez, Mercedes Molina-Morales, Marta Precioso, and Jesus Avilés (from the Universidad de Granada and Estación Experimental de Zonas Áridas, in Spain) are studying magpies (Pica pica) at a location in South-eastern Spain (La Calahorra, Granada). Magpies are regularly parasitized by great spotted cuckoos (Clamator glandarius), and the team have been following female magpies during their lives for the last 12 years, recording parasitism status and foreign egg rejection of individuals of known-age over their lifetime. They found that the likelihood of being parasitized does not change as females age, although there is a trend that longer-lived females are parasitized less often. However, foreign egg rejection probability does increase with age: even though many females never reject foreign eggs in their nests, most females that do it start rejecting when they are 3 or 4 years old. It is known that magpies may live many years, but most females in the study population are young, and so the majority of them accepted foreign eggs; this suggest that brood parasites exploit younger hosts, benefitting from a lower defensive level. Abstract When the strength or nature of a host -parasite interaction changes over the host life cycle, the consequences of parasitism can depend on host population age structure. Avian brood parasites reduce hosts’ breeding success, and host age may play a role in this interaction if younger hosts are more likely parasitized and/or less able to defend themselves. We analyzed whether the age of female magpies (Pica pica) hosts is associated with parasite attack or their ability to reject foreign eggs. We recorded parasitism and model egg rejection of known-age individuals over their lifetime, and established whether likelihood of parasitism or egg rejection changed with age or longevity. Parasitism probability did not change with female age and there was a trend for longer lived females to be less likely to be parasitized. However, model egg rejection probability increased with age for each individual female, and longer-lived females were more prone to reject. Most females in the population were young, and the majority of them accepted model eggs, suggesting that brood parasites exploiting younger host individuals are benefitting from a lower defensive level of their hosts. Our results stress that the intensity of selection by brood parasites may be mediated by the age-structure of host populations, a so far neglected aspect in brood parasite-host research. More forthcoming papers &raquo; <p>Juan Gabriel Mart&iacute;nez, Mercedes Molina-Morales, Marta Precioso, and Jes&uacute;s Miguel Avil&eacute;s (May 2020)</p> <p><b>We show that individual hosts of a cuckoo species change the expression of their main defensive behaviour as they age </b></p> <p><i><a href="https://dx.doi.org/10.1086/708155">Read the Article</a></i> (Just Accepted)</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;">B</span>reeding for some birds ends up in a disaster: instead of rearing their own healthy chicks, they take care of intruders, the cuckoos, which get rid of any legitimate offspring in the nest and monopolize all the care that host parents should be providing to their nestlings. But hosts of brood parasites are not always parasitized, and if they do, they may not be defenseless, since some individuals are able to recognize and reject cuckoo eggs. If natural selection favors individuals able to avoid parasitism, why do some individuals escape parasitism and/or are able to reject cuckoo eggs, whereas others become victims of the parasites? This article explores how considering the age of individual hosts may help to answer this. </p><p>Researchers Juan Gabriel Martínez, Mercedes Molina-Morales, Marta Precioso, and Jesus Avilés (from the Universidad de Granada and Estación Experimental de Zonas Áridas, in Spain) are studying magpies (<i>Pica pica</i>) at a location in South-eastern Spain (La Calahorra, Granada). Magpies are regularly parasitized by great spotted cuckoos (<i>Clamator glandarius</i>), and the team have been following female magpies during their lives for the last 12 years, recording parasitism status and foreign egg rejection of individuals of known-age over their lifetime. They found that the likelihood of being parasitized does not change as females age, although there is a trend that longer-lived females are parasitized less often. However, foreign egg rejection probability does increase with age: even though many females never reject foreign eggs in their nests, most females that do it start rejecting when they are 3 or 4 years old. It is known that magpies may live many years, but most females in the study population are young, and so the majority of them accepted foreign eggs; this suggest that brood parasites exploit younger hosts, benefitting from a lower defensive level. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">W</span>hen the strength or nature of a host -parasite interaction changes over the host life cycle, the consequences of parasitism can depend on host population age structure. Avian brood parasites reduce hosts’ breeding success, and host age may play a role in this interaction if younger hosts are more likely parasitized and/or less able to defend themselves. We analyzed whether the age of female magpies (<i>Pica pica</i>) hosts is associated with parasite attack or their ability to reject foreign eggs. We recorded parasitism and model egg rejection of known-age individuals over their lifetime, and established whether likelihood of parasitism or egg rejection changed with age or longevity. Parasitism probability did not change with female age and there was a trend for longer lived females to be less likely to be parasitized. However, model egg rejection probability increased with age for each individual female, and longer-lived females were more prone to reject. Most females in the population were young, and the majority of them accepted model eggs, suggesting that brood parasites exploiting younger host individuals are benefitting from a lower defensive level of their hosts. Our results stress that the intensity of selection by brood parasites may be mediated by the age-structure of host populations, a so far neglected aspect in brood parasite-host research. </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, 15 Jan 2020 06:00:00 GMT “Frequency of occurrence and population-dynamic consequences of different forms of density-dependent emigration” https://amnat.org/an/newpapers/May-Harman.html Rachel R. Harman, Jerome Goddard II, Ratnasingham Shivaji, and James T. Cronin (May 2020) Density-dependent emigration (DDE) is more diverse than we thought! Review & population persistence of 5 forms of DDE Read the Article (Just Accepted) Individuals will emigrate from a patch for several reasons including to escape competition, avoid predators, find resources, or form a group. These emigrants in turn affect colonization and local densities of patches around the landscape, which can lead to changes in population persistence. The proportion of the population emigrating based on density (density-dependent emigration; DDE), has been widely accepted to be density-independent or positive density-dependent (DIE and +DDE respectively; see figure). However, other forms of DDE (see figure) are biologically possible. But do these other forms of DDE even exist in nature? To answer this, Harman and associates reviewed 145 empirical studies of DDE to examine the range and frequency of each DDE relationship. As expected, the majority of these studies represented DIE and +DDE results; however, they regularly found the other forms of DDE (negative, u-shaped, and hump-shaped; see figure). So, do these rare forms of DDE matter to population stability? Harman and associates claim that they do, particularly in small patches commonly found in fragmented landscapes. Using models incorporating patch size and landscape quality, the authors show that population persistence changes with the form of DDE. Negative and u-shape DDE forms allow for populations to survive in smaller patches, but at the risk of sudden extinction. Additionally, negative and hump-shaped DDE forms allow for different sized populations to persist in same-sized patches. Harman and associates suggest that to limit bias against detecting non-linear DDE forms in nature, future research should utilize methods that include wider ranges of density treatments and statistics that test for all forms of DDE. With further investigation of these forms of DDE, better predictions for species conservation (such as metapopulation extinction and invasive species movement) are possible as the form of emigration can change if a population will persist. Abstract Emigration is a fundamental process affecting species local, regional, and large-scale dynamics. The paradigmatic view in ecology is that emigration is density independent (DIE) or positive density-dependent (+DDE). However, alternative forms are biologically plausible, including negative (&minus;DDE), u-shaped (uDDE), and hump-shaped (hDDE) forms. We reviewed the empirical literature to assess the frequency of different forms of density-dependent emigration and whether the form depended on methodology. We also developed a reaction-diffusion model to illustrate how different forms of DDE can affect patch-level population persistence. We found 145 studies, the majority representing DIE (30%) and +DDE (36%). However, we also regularly found &minus;DDE (25%) and evidence for nonlinear DDE (9%), including one case of uDDE and two cases of hDDE. Nonlinear DDE detection is likely hindered by the use of few density levels and small density ranges. Based on our models, DIE and +DDE promoted stable and persistent populations. uDDE and &minus;DDE generated an Allee effect that decreases minimum patch size. Lastly, &minus;DDE and hDDE models yielded bistability that allows the establishment of populations at lower densities. We conclude that the emigration process can be a diverse function of density in nature and that alternative DDE forms can have important consequences for population dynamics. &emsp; More forthcoming papers &raquo; <p>Rachel R. Harman, Jerome Goddard II, Ratnasingham Shivaji, and James T. Cronin (May 2020) </p> <p><b>Density-dependent emigration (DDE) is more diverse than we thought! Review & population persistence of 5 forms of DDE </b></p> <p><i><a href="https://dx.doi.org/10.1086/708156">Read the Article</a></i> (Just Accepted) </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;">I</span>ndividuals will emigrate from a patch for several reasons including to escape competition, avoid predators, find resources, or form a group. These emigrants in turn affect colonization and local densities of patches around the landscape, which can lead to changes in population persistence. The proportion of the population emigrating based on density (density-dependent emigration; DDE), has been widely accepted to be density-independent or positive density-dependent (DIE and +DDE respectively; see figure). However, other forms of DDE (see figure) are biologically possible.</p> <p>But do these other forms of DDE even exist in nature? To answer this, Harman and associates reviewed 145 empirical studies of DDE to examine the range and frequency of each DDE relationship. As expected, the majority of these studies represented DIE and +DDE results; however, they regularly found the other forms of DDE (negative, u-shaped, and hump-shaped; see figure).</p> <p>So, do these rare forms of DDE matter to population stability? Harman and associates claim that they do, particularly in small patches commonly found in fragmented landscapes. Using models incorporating patch size and landscape quality, the authors show that population persistence changes with the form of DDE. Negative and u-shape DDE forms allow for populations to survive in smaller patches, but at the risk of sudden extinction. Additionally, negative and hump-shaped DDE forms allow for different sized populations to persist in same-sized patches.</p> <p>Harman and associates suggest that to limit bias against detecting non-linear DDE forms in nature, future research should utilize methods that include wider ranges of density treatments and statistics that test for all forms of DDE. With further investigation of these forms of DDE, better predictions for species conservation (such as metapopulation extinction and invasive species movement) are possible as the form of emigration can change if a population will persist.</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>migration is a fundamental process affecting species local, regional, and large-scale dynamics. The paradigmatic view in ecology is that emigration is density independent (DIE) or positive density-dependent (+DDE). However, alternative forms are biologically plausible, including negative (&minus;DDE), u-shaped (uDDE), and hump-shaped (hDDE) forms. We reviewed the empirical literature to assess the frequency of different forms of density-dependent emigration and whether the form depended on methodology. We also developed a reaction-diffusion model to illustrate how different forms of DDE can affect patch-level population persistence. We found 145 studies, the majority representing DIE (30%) and +DDE (36%). However, we also regularly found &minus;DDE (25%) and evidence for nonlinear DDE (9%), including one case of uDDE and two cases of hDDE. Nonlinear DDE detection is likely hindered by the use of few density levels and small density ranges. Based on our models, DIE and +DDE promoted stable and persistent populations. uDDE and &minus;DDE generated an Allee effect that decreases minimum patch size. Lastly, &minus;DDE and hDDE models yielded bistability that allows the establishment of populations at lower densities. We conclude that the emigration process can be a diverse function of density in nature and that alternative DDE forms can have important consequences for population dynamics. &emsp;</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, 14 Jan 2020 06:00:00 GMT “Mechanisms for color convergence in a mimetic radiation of poison frogs” https://amnat.org/an/newpapers/May-Twomey.html Evan Twomey, Morgan Kain, Myriam Claeys, Kyle Summers, Santiago Castroviejo-Fisher, and Ines Van Bocxlaer (May 2020) Color in poison frogs (Dendrobatidae) is mostly structural Read the Article (Just Accepted) Mimicry is an adaptation where one species evolves color similarity to another species to avoid predation. Often, a single species evolves resemblance to multiple species, leading to color variation in the mimic species. How these shared colors evolve among distant relatives and how a single species is capable of evolving a suite of colors to matching multiple species is not well understood. We studied the mechanisms underlying color mimicry in the Peruvian poison dart frog species Ranitomeya imitator, and found that color variation and mimicry is largely controlled by the thickness of nanocrystals in the skin. These crystals are responsible for the structural color of the skin, which results in highly reflective coloration that may be important for producting effective warning coloration to avoid predation. Other species of poison dart frogs, including the species mimicked by Ranitomeya imitator as well as other poison dart frogs not involved in mimicry, also regulate color through structural mechanisms. These results demonstrate that much of the color diversity seen across poison frogs, including mimetic colors, is controlled by a single trait: the thickness of reflective nanocrystals in the skin. Mimicry appears to have evolved from a common set of color mechanisms found across poison dart frogs, rather than from novel color mechanisms having evolved ‘from scratch’ in the mimetic species. These results add further weight to the idea that convergent evolution often occurs through parallel evolution within a shared set of developmental pathways rather than the evolution of completely novel structures. Abstract In animals, bright colors often evolve to mimic other species when a resemblance is selectively favored. Understanding the proximate mechanisms underlying such color mimicry can give insights into how mimicry evolves, for example, whether color convergence evolves from a shared set of mechanisms or through the evolution of novel color production mechanisms. We studied color production mechanisms in poison frogs (Dendrobatidae), focusing on the mimicry complex of Ranitomeya imitator. Using reflectance spectrometry, skin pigment analysis, electron microscopy, and color modeling, we found that the bright colors of these frogs, both within and outside the mimicry complex, are largely structural and produced by iridophores, but that color production depends crucially on interactions with pigments. Color variation and mimicry is regulated predominantly by iridophore platelet thickness and, to a lesser extent, concentration of the red pteridine pigment drosopterin. Compared to each of the four morphs of model species which it resembles, R.&nbsp;imitator displays greater variation in both structural and pigmentary mechanisms, which may have facilitated phenotypic divergence in this species. Analyses of non-mimetic dendrobatids in other genera demonstrate that these mechanisms are widespread within the family, and that poison frogs share a complex physiological “color palette” that can produce diverse and highly reflective colors. More forthcoming papers &raquo; <p>Evan Twomey, Morgan Kain, Myriam Claeys, Kyle Summers, Santiago Castroviejo-Fisher, and Ines Van Bocxlaer (May 2020) </p> <p><b>Color in poison frogs (Dendrobatidae) is mostly structural </b></p> <p><i><a href="https://dx.doi.org/10.1086/708157">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>imicry is an adaptation where one species evolves color similarity to another species to avoid predation. Often, a single species evolves resemblance to multiple species, leading to color variation in the mimic species. How these shared colors evolve among distant relatives and how a single species is capable of evolving a suite of colors to matching multiple species is not well understood. We studied the mechanisms underlying color mimicry in the Peruvian poison dart frog species <i>Ranitomeya imitator</i>, and found that color variation and mimicry is largely controlled by the thickness of nanocrystals in the skin. These crystals are responsible for the structural color of the skin, which results in highly reflective coloration that may be important for producting effective warning coloration to avoid predation. Other species of poison dart frogs, including the species mimicked by <i>Ranitomeya imitator</i> as well as other poison dart frogs not involved in mimicry, also regulate color through structural mechanisms. These results demonstrate that much of the color diversity seen across poison frogs, including mimetic colors, is controlled by a single trait: the thickness of reflective nanocrystals in the skin. Mimicry appears to have evolved from a common set of color mechanisms found across poison dart frogs, rather than from novel color mechanisms having evolved ‘from scratch’ in the mimetic species. These results add further weight to the idea that convergent evolution often occurs through parallel evolution within a shared set of developmental pathways rather than the evolution of completely novel structures. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>n animals, bright colors often evolve to mimic other species when a resemblance is selectively favored. Understanding the proximate mechanisms underlying such color mimicry can give insights into how mimicry evolves, for example, whether color convergence evolves from a shared set of mechanisms or through the evolution of novel color production mechanisms. We studied color production mechanisms in poison frogs (Dendrobatidae), focusing on the mimicry complex of <i>Ranitomeya imitator</i>. Using reflectance spectrometry, skin pigment analysis, electron microscopy, and color modeling, we found that the bright colors of these frogs, both within and outside the mimicry complex, are largely structural and produced by iridophores, but that color production depends crucially on interactions with pigments. Color variation and mimicry is regulated predominantly by iridophore platelet thickness and, to a lesser extent, concentration of the red pteridine pigment drosopterin. Compared to each of the four morphs of model species which it resembles, <i>R.&nbsp;imitator</i> displays greater variation in both structural and pigmentary mechanisms, which may have facilitated phenotypic divergence in this species. Analyses of non-mimetic dendrobatids in other genera demonstrate that these mechanisms are widespread within the family, and that poison frogs share a complex physiological “color palette” that can produce diverse and highly reflective colors. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Tue, 14 Jan 2020 06:00:00 GMT “Selection for rhythm as a trigger for recursive evolution in the elaborate display system of woodpeckers” https://amnat.org/an/newpapers/May-Miles.html Meredith C. Miles, Eric R. Schuppe, and Matthew J. Fuxjager (May 2020) Display rhythm fosters premating isolation early in a species history, but then impedes signal evolution later on Read the Article (Just Accepted)Selection pressures that influences how traits evolve change over time. A consequence of this phenomenon is that selection regimes acting on a trait early in its history can affect how that same trait evolves later on in response to a different selection regime. We study this process in woodpeckers by looking at the evolution of their territorial display, the drum. Individuals produce this iconic signal when they rapidly hammer their bill against trees and other substrates in the environment, warding off potential interlopers during the breeding season. Nearly all 200 woodpecker species drum, but each species differs in terms of its drum speed and length. Here, we report that species also differ with regard to drum rhythm—some woodpeckers drum at constant rates, whereas others change their drum speed following basic mathematical functions (e.g., a linear increase in speed, an exponential decay in speed, etc.). Using various comparative analyses, we show that rhythm is the key feature of the drum that diverges between closely related species overlapping in their geographic range. Such ‘character displacement’ is thought to help species better recognize their own, but the strength of this selective process diminishes overtime as other traits evolve to help mediate this ability. Additionally, we show that rhythm can enhance or inhibit the evolutionary exaggeration of drum speed and length. This is important because this latter feature is favored by contemporary sexual selection to help support territoriality. Thus, selection early in a woodpecker’s history can influence the structure of a drum display in ways that impact how the signal evolves down the road. This may help explain why similar selection regimes that act on separate taxa often result in the emergence of completely different phenotypes. Abstract Evolution is never truly predictable, partially because selection is a recursive process: it operates on its own output to generate historical contingencies, so emergent traits can reshape how others evolve in the future. Studies rarely attempt to directly trace how recursion underlies present-day phenotypic pattern on a macroevolutionary basis. To address this gap, we examined how different selection regimes—each operating on a different timescale— recursively guide the evolution of the woodpecker drum display. Some 200 species drum with distinctive speed and length, which are important for territorial competition. Here we report remarkable variation in drum rhythm, with some species drumming at constant rates and others changing speed along a range of mathematical functions. Rhythm undergoes divergent character displacement among sympatric sister species, a process that wanes as other reproductive boundaries emerge over time. Tracing the recursive effects of this process, we found that modifying rhythm potentiates or constraints speed/length elaboration. Additionally, increased sexual size dimorphism predicts the emergence of rhythms associated with constrained evolutionary rates of speed/length, implying that selection can also constrain itself. Altogether, our findings illustrate how recursion introduces contingencies that allow diverse phenotypes to arise from similar selection regimes. More forthcoming papers &raquo; <p>Meredith C. Miles, Eric R. Schuppe, and Matthew J. Fuxjager (May 2020)</p> <p><b>Display rhythm fosters premating isolation early in a species history, but then impedes signal evolution later on </b></p> <p><i><a href="https://dx.doi.org/10.1086/707748">Read the Article</a></i> (Just Accepted)</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>election pressures that influences how traits evolve change over time. A consequence of this phenomenon is that selection regimes acting on a trait early in its history can affect how that same trait evolves later on in response to a different selection regime. We study this process in woodpeckers by looking at the evolution of their territorial display, the drum. Individuals produce this iconic signal when they rapidly hammer their bill against trees and other substrates in the environment, warding off potential interlopers during the breeding season. Nearly all 200 woodpecker species drum, but each species differs in terms of its drum speed and length. Here, we report that species also differ with regard to drum rhythm—some woodpeckers drum at constant rates, whereas others change their drum speed following basic mathematical functions (e.g., a linear increase in speed, an exponential decay in speed, etc.). Using various comparative analyses, we show that rhythm is the key feature of the drum that diverges between closely related species overlapping in their geographic range. Such ‘character displacement’ is thought to help species better recognize their own, but the strength of this selective process diminishes overtime as other traits evolve to help mediate this ability. Additionally, we show that rhythm can enhance or inhibit the evolutionary exaggeration of drum speed and length. This is important because this latter feature is favored by contemporary sexual selection to help support territoriality. Thus, selection early in a woodpecker’s history can influence the structure of a drum display in ways that impact how the signal evolves down the road. This may help explain why similar selection regimes that act on separate taxa often result in the emergence of completely different phenotypes. </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>volution is never truly predictable, partially because selection is a recursive process: it operates on its own output to generate historical contingencies, so emergent traits can reshape how others evolve in the future. Studies rarely attempt to directly trace how recursion underlies present-day phenotypic pattern on a macroevolutionary basis. To address this gap, we examined how different selection regimes—each operating on a different timescale— recursively guide the evolution of the woodpecker drum display. Some 200 species drum with distinctive speed and length, which are important for territorial competition. Here we report remarkable variation in drum rhythm, with some species drumming at constant rates and others changing speed along a range of mathematical functions. Rhythm undergoes divergent character displacement among sympatric sister species, a process that wanes as other reproductive boundaries emerge over time. Tracing the recursive effects of this process, we found that modifying rhythm potentiates or constraints speed/length elaboration. Additionally, increased sexual size dimorphism predicts the emergence of rhythms associated with constrained evolutionary rates of speed/length, implying that selection can also constrain itself. Altogether, our findings illustrate how recursion introduces contingencies that allow diverse phenotypes to arise from similar selection regimes. </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, 19 Dec 2019 06:00:00 GMT “Ecology and evolution of blood oxygen-carrying capacity in birds” https://amnat.org/an/newpapers/May-Minias.html Piotr Minias (May 2020) A comparative study identifies major ecological and biogeographical correlates of avian blood oxygen-carrying capacity Read the Article (Just Accepted) Physiological characters are commonly thought to be highly plastic within individuals and show great variation between individuals within populations. However, it is often still possible to identify major evolutionary forces shaping inter-specific variation in physiology. In this paper, Piotr Minias from University of Łódź in Poland, used an extensive dataset on haematocrit and blood haemoglobin concentration measurements to track the evolution of blood oxygen-carrying capacity in birds. The analysis of published data for 300 avian species revealed several macroevolutionary and macroecological patterns in the traits that play a key role in blood oxygen transport. The scientist showed that biogeographical distribution is one of the most important predictors of blood oxygen-carrying capacity in birds, as high-latitude and polar species, as well as those living at high altitudes show more efficient blood oxygen transport. These results were consistent with hypotheses that oxidative metabolism is higher in colder climate due to increased thermoregulatory costs, and that enhanced oxygen-carrying capacity of blood should compensate for reduced partial oxygen pressure at high latitudes. Also, higher metabolic performance of smaller birds favored the evolution of higher haematocrits and haemoglobin concentrations in blood. Consistently, the lowest blood oxygen-carrying capacity was recorded in large non-passerines, while the evolution of both haematocrit and haemoglobin concentration proceeded via fluctuating selection towards higher values in younger avian lineages, including many passerine families. The paper not only reconstructs evolutionary history of important physiological traits in birds, but it also gives a novel insight into their functional variation from the macroevolutionary point of view. Abstract Blood oxygen-carrying capacity is one of important determinants of oxygen amounts supplied to the tissues per unit time and plays a key role in oxidative metabolism. In wild vertebrates, blood oxygen-carrying capacity is most commonly measured with the total blood haemoglobin concentration (Hb) and haematocrit (Hct), which is the volume percentage of red blood cells in blood. Here, I used published estimates of avian Hb and Hct (nearly one thousand estimates from 300 species) to examine macroevolutionary patterns in blood oxygen-carrying capacity of blood in birds. Phylogenetically-informed comparative analysis indicated that blood oxygen-carrying capacity was primarily determined by species distribution (latitude and elevation) and morphological constraints (body mass). I found little support for the effect of life history components on blood oxygen-carrying capacity, except for a positive association of Hct with clutch size. Hb was also positively associated with diving behavior, but I found no effect of migratoriness on either Hb or Hct. Fluctuating selection was identified as the major force shaping the evolution of blood oxygen-carrying capacity. The results offer novel insights into the evolution of Hb and Hct in birds, as well as they provide a general, phylogenetically-robust support for some long-standing hypotheses in avian ecophysiology. More forthcoming papers &raquo; <p>Piotr Minias (May 2020) </p> <p><b>A comparative study identifies major ecological and biogeographical correlates of avian blood oxygen-carrying capacity </b></p> <p><i><a href="https://dx.doi.org/10.1086/707720">Read the Article</a></i> (Just Accepted) </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>hysiological characters are commonly thought to be highly plastic within individuals and show great variation between individuals within populations. However, it is often still possible to identify major evolutionary forces shaping inter-specific variation in physiology. In this paper, Piotr Minias from University of Łódź in Poland, used an extensive dataset on haematocrit and blood haemoglobin concentration measurements to track the evolution of blood oxygen-carrying capacity in birds. The analysis of published data for 300 avian species revealed several macroevolutionary and macroecological patterns in the traits that play a key role in blood oxygen transport. The scientist showed that biogeographical distribution is one of the most important predictors of blood oxygen-carrying capacity in birds, as high-latitude and polar species, as well as those living at high altitudes show more efficient blood oxygen transport. These results were consistent with hypotheses that oxidative metabolism is higher in colder climate due to increased thermoregulatory costs, and that enhanced oxygen-carrying capacity of blood should compensate for reduced partial oxygen pressure at high latitudes. Also, higher metabolic performance of smaller birds favored the evolution of higher haematocrits and haemoglobin concentrations in blood. Consistently, the lowest blood oxygen-carrying capacity was recorded in large non-passerines, while the evolution of both haematocrit and haemoglobin concentration proceeded via fluctuating selection towards higher values in younger avian lineages, including many passerine families. The paper not only reconstructs evolutionary history of important physiological traits in birds, but it also gives a novel insight into their functional variation from the macroevolutionary point of view. </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;">B</span>lood oxygen-carrying capacity is one of important determinants of oxygen amounts supplied to the tissues per unit time and plays a key role in oxidative metabolism. In wild vertebrates, blood oxygen-carrying capacity is most commonly measured with the total blood haemoglobin concentration (Hb) and haematocrit (Hct), which is the volume percentage of red blood cells in blood. Here, I used published estimates of avian Hb and Hct (nearly one thousand estimates from 300 species) to examine macroevolutionary patterns in blood oxygen-carrying capacity of blood in birds. Phylogenetically-informed comparative analysis indicated that blood oxygen-carrying capacity was primarily determined by species distribution (latitude and elevation) and morphological constraints (body mass). I found little support for the effect of life history components on blood oxygen-carrying capacity, except for a positive association of Hct with clutch size. Hb was also positively associated with diving behavior, but I found no effect of migratoriness on either Hb or Hct. Fluctuating selection was identified as the major force shaping the evolution of blood oxygen-carrying capacity. The results offer novel insights into the evolution of Hb and Hct in birds, as well as they provide a general, phylogenetically-robust support for some long-standing hypotheses in avian ecophysiology. </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, 19 Dec 2019 06:00:00 GMT “Revisiting a landmark study-system: no evidence for a punctuated mode of evolution in <i>Metrarabdotos</i>” https://amnat.org/an/newpapers/May-Voje.html Kjetil Lysne Voje, Emanuela Di Martino, and Arthur Porto (May 2019) Reanalysis of the best example of punctuated evolution (Metrarabdotos) finds no evidence of punctuated evolution Read the Article (Just Accepted) The fossil record is our only direct source of information on how evolution proceeds on timescales beyond a few centuries. How we analyze and interpret fossil data is therefore fundamental for our understanding of the processes that govern the evolution of life on Earth. Stephen J. Gould and Niles Eldredge’s rereading of the fossil record – claiming species remain more or less unaltered during their existence with major and rapid evolutionary change happening during speciation events – started a heated debate within paleontology and evolutionary biology, which holds to this day. The bryozoan genus Metrarabdotos is generally considered the best example of punctuated evolution in the fossil record. Gould called Metrarabdotos “the most brilliantly persuasive, and most meticulously documented, example ever presented for predominant (in this case, exclusive) punctuated equilibrium in a full lineage” (Gould 2002, page 827). Evolutionary biologists Kjetil L. Voje and Arthur Porto at the University of Oslo, together with bryozoologist and paleontologist Emanuela Di Martino at the Natural History Museum in Oslo, have reanalyzed the original Metrarabdotos data. The authors point out critical methodological issues in the original work on Metrarabdotos. One issue is related to what is called measurement theory. For example, biologists use different scale types when they describe the morphology of a species. The length of a character in millimeters is a different scale type than the scoring of a character as present or absent. The scale type restricts what kind of statistical analyses and inferences that can be drawn from the numbers, but this principle was violated in much of the original work on Metrarabdotos. The authors find no evidence for punctuated evolution within Metrarabdotos in their reanalysis of the data, when taking the methodological issues into account. Abstract Is speciation generally a ‘special time’ in morphological evolution or are lineage splitting events just ‘more of the same’ where the end product happens to be two separate lineages? Data on evolutionary dynamics during anagenetic and cladogenetic events among closely related lineages within a clade are rare, but the fossil record of the bryozoan genus Metrarabdotos is considered a textbook example of a clade where speciation causes rapid evolutionary change against a backdrop of morphological stasis within lineages. Here, we point to some measurement theoretical and methodological issues in the original work on Metrarabdotos. We then reanalyze a subset of the original data that can be meaningfully investigated using similar quantitative statistical approaches as in the original studies. We consistently fail in finding variation in the evolutionary process during within-lineage evolution compared to cladogenetic events: Neither the rates of evolution, the strength of selection or the directions traveled in multivariate morphospace are different when comparing evolution within lineages and at speciation events in Metrarabdotos, and genetic drift cannot be excluded as a sufficient explanation for the morphological differentiation within lineages and during speciation. Although widely considered the best example of a punctuated mode of evolution, morphological divergence and speciation are not linked in Metrarabdotos. More forthcoming papers &raquo; <p>Kjetil Lysne Voje, Emanuela Di Martino, and Arthur Porto (May 2019) </p> <p><b>Reanalysis of the best example of punctuated evolution (<i>Metrarabdotos</i>) finds no evidence of punctuated evolution </b></p> <p><i><a href="https://dx.doi.org/10.1086/707664">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he fossil record is our only direct source of information on how evolution proceeds on timescales beyond a few centuries. How we analyze and interpret fossil data is therefore fundamental for our understanding of the processes that govern the evolution of life on Earth. </p><p>Stephen J. Gould and Niles Eldredge’s rereading of the fossil record – claiming species remain more or less unaltered during their existence with major and rapid evolutionary change happening during speciation events – started a heated debate within paleontology and evolutionary biology, which holds to this day. The bryozoan genus <i>Metrarabdotos</i> is generally considered the best example of punctuated evolution in the fossil record. Gould called <i>Metrarabdotos</i> “the most brilliantly persuasive, and most meticulously documented, example ever presented for predominant (in this case, exclusive) punctuated equilibrium in a full lineage” (Gould 2002, page 827). </p><p>Evolutionary biologists Kjetil L. Voje and Arthur Porto at the University of Oslo, together with bryozoologist and paleontologist Emanuela Di Martino at the Natural History Museum in Oslo, have reanalyzed the original <i>Metrarabdotos</i> data. </p><p>The authors point out critical methodological issues in the original work on <i>Metrarabdotos</i>. One issue is related to what is called measurement theory. For example, biologists use different scale types when they describe the morphology of a species. The length of a character in millimeters is a different scale type than the scoring of a character as present or absent. The scale type restricts what kind of statistical analyses and inferences that can be drawn from the numbers, but this principle was violated in much of the original work on <i>Metrarabdotos</i>. </p><p>The authors find no evidence for punctuated evolution within <i>Metrarabdotos</i> in their reanalysis of the data, when taking the methodological issues into account.</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>s speciation generally a ‘special time’ in morphological evolution or are lineage splitting events just ‘more of the same’ where the end product happens to be two separate lineages? Data on evolutionary dynamics during anagenetic and cladogenetic events among closely related lineages within a clade are rare, but the fossil record of the bryozoan genus <i>Metrarabdotos</i> is considered a textbook example of a clade where speciation causes rapid evolutionary change against a backdrop of morphological stasis within lineages. Here, we point to some measurement theoretical and methodological issues in the original work on <i>Metrarabdotos</i>. We then reanalyze a subset of the original data that can be meaningfully investigated using similar quantitative statistical approaches as in the original studies. We consistently fail in finding variation in the evolutionary process during within-lineage evolution compared to cladogenetic events: Neither the rates of evolution, the strength of selection or the directions traveled in multivariate morphospace are different when comparing evolution within lineages and at speciation events in <i>Metrarabdotos</i>, and genetic drift cannot be excluded as a sufficient explanation for the morphological differentiation within lineages and during speciation. Although widely considered the best example of a punctuated mode of evolution, morphological divergence and speciation are not linked in <i>Metrarabdotos</i>. </p> <div style="float: right;"><a href="http://www.amnat.org/an/newpapers.html"> <span style="font-size: large; font-family: Georgia;"><i>More forthcoming papers</i> &raquo;</span></a></div> Thu, 19 Dec 2019 06:00:00 GMT “Increased levels of perceived competition decrease juvenile kin-shoaling preferences in a cichlid fish” https://amnat.org/an/newpapers/May-Thuenken-A.html Timo Thünken, Saskia Hesse, and Denis Meuthen (May 2020) Kin competition can decrease indirect fitness. High perceived competition induces kin avoidance in juvenile cichlids Read the Article (Just Accepted) Abstract Inclusive fitness theory predicts that individuals can increase their indirect fitness by grouping with kin. However, kin-grouping also increases competition between kin, which potentially outweighs its benefits. The level of kin-competition is contingent on environmental conditions and thus highly variable. Hence, individuals should benefit from plastically adjusting kin-discrimination according to the expected level of kin competition. Here, we investigate whether perceived high competition affects juvenile kin-shoaling preferences in the cichlid Pelvicachromis taeniatus. Juveniles were given the choice between two shoals consisting of either kin or non-kin. Levels of perceived competition were manipulated through food limitation in the face of the differential energy expenditure of differently sized fish. The preference to shoal with kin decreased with increasing levels of perceived competition; small food-deprived individuals avoided kin. Shoaling with kin under strong competition may reduce individual indirect fitness. Hence, individuals can likely improve their inclusive fitness by plastically adjusting their kin-grouping preferences. More forthcoming papers &raquo; <p>Timo Thünken, Saskia Hesse, and Denis Meuthen (May 2020) </p> <p><b>Kin competition can decrease indirect fitness. High perceived competition induces kin avoidance in juvenile cichlids </b></p> <p><i><a href="https://dx.doi.org/10.1086/707747">Read the Article</a></i> (Just Accepted) </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>nclusive fitness theory predicts that individuals can increase their indirect fitness by grouping with kin. However, kin-grouping also increases competition between kin, which potentially outweighs its benefits. The level of kin-competition is contingent on environmental conditions and thus highly variable. Hence, individuals should benefit from plastically adjusting kin-discrimination according to the expected level of kin competition. Here, we investigate whether perceived high competition affects juvenile kin-shoaling preferences in the cichlid <i>Pelvicachromis taeniatus</i>. Juveniles were given the choice between two shoals consisting of either kin or non-kin. Levels of perceived competition were manipulated through food limitation in the face of the differential energy expenditure of differently sized fish. The preference to shoal with kin decreased with increasing levels of perceived competition; small food-deprived individuals avoided kin. Shoaling with kin under strong competition may reduce individual indirect fitness. Hence, individuals can likely improve their inclusive fitness by plastically adjusting their kin-grouping preferences. </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, 19 Dec 2019 06:00:00 GMT “Ecological limits as the driver of bird species richness patterns along the east Himalayan elevational gradient” https://amnat.org/an/newpapers/May-Schumm.html Matthew Schumm, Alex E. White, K. Supriya, and Trevor D. Price (May 2020) Himalayan bird species pack into niche space where resources are more abundant, at middle elevations Read the Article (Just Accepted) For decades, ecologists have been trying to understand why some places have many more species of plants and animals than others. In the east Himalaya, about 100 more bird species breed in the middle elevations (1000-2000 meters above sea level) than at the bottom of the mountain or in high-elevation forests. Many of the species that live together are closely related to each other, look similar, and eat similar insects and spiders. These birds’ similarity despite their coexistence has been taken to imply that competition for food is a relatively unimportant factor in determining which bird species are found where. However, Matthew Schumm and colleagues challenge this view. They show that the pattern of bird species numbers and species traits in the east Himalaya matches the pattern of prey insect numbers and sizes available at different elevations. This implies that amount and type of available food is likely a major determinant of where bird populations can survive and breed. The authors compare bird body and beak shapes and sizes and feeding habits with insect numbers and sizes at various elevations. They show that larger numbers of small insects are present at the middle elevations in the summer. The greater number of small insects appears to support the coexistence of closely related small-bodied and small-beaked insect-eating bird species. The authors then look at patterns of bird traits and insect numbers along other mountain ranges in tropical Ecuador, Tanzania, and New Guinea and find that patterns of bird beak size match patterns of insect size. The authors argue that resource availability likely plays an important role in shaping bird diversity patterns globally.Abstract Variation in species richness across environmental gradients results from a combination of historical non-equilibrium processes (time, speciation, extinction) and present-day differences in environmental carrying capacities (i.e., ecological limits, affected by species interactions and the abundance and diversity of resources). In a study of bird richness along the sub-tropical east Himalayan elevational gradient, we test the prediction that species richness patterns are consistent with ecological limits using data on morphology, phylogeny, elevational distribution, and arthropod resources. Species richness peaks at mid-elevations. Occupied morphological volume is roughly constant from low to mid-elevations, implying more species are packed into the same space at mid-elevations compared with low elevations. However, variance in beak length, and differences in beak length between close relatives decline with elevation, a consequence of the addition of many small insectivores at mid-elevations. These patterns are predicted from resource distributions: arthropod size diversity declines from low to mid elevations, largely because many more small insects are present at mid-elevations. Weak correlations of species mean morphological traits with elevation also match predictions based on resources and habitats. Elevational transects in the tropical Andes, New Guinea, and Tanzania similarly show declines in mean arthropod size and mean beak length, and in these cases likely contribute to declining numbers of insectivorous bird species richness along these gradients. The results imply conditions for ecological limits are met, although historical non-equilibrium processes are likely to also contribute to the pattern of species richness. More forthcoming papers &raquo; <p>Matthew Schumm, Alex E. White, K. Supriya, and Trevor D. Price (May 2020) </p> <p><b>Himalayan bird species pack into niche space where resources are more abundant, at middle elevations </b></p> <p><i><a href="https://dx.doi.org/10.1086/707665">Read the Article</a></i> (Just Accepted) </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;">F</span>or decades, ecologists have been trying to understand why some places have many more species of plants and animals than others. In the east Himalaya, about 100 more bird species breed in the middle elevations (1000-2000 meters above sea level) than at the bottom of the mountain or in high-elevation forests. Many of the species that live together are closely related to each other, look similar, and eat similar insects and spiders. These birds&rsquo; similarity despite their coexistence has been taken to imply that competition for food is a relatively unimportant factor in determining which bird species are found where. However, Matthew Schumm and colleagues challenge this view. They show that the pattern of bird species numbers and species traits in the east Himalaya matches the pattern of prey insect numbers and sizes available at different elevations. This implies that amount and type of available food is likely a major determinant of where bird populations can survive and breed.</p> <p>The authors compare bird body and beak shapes and sizes and feeding habits with insect numbers and sizes at various elevations. They show that larger numbers of small insects are present at the middle elevations in the summer. The greater number of small insects appears to support the coexistence of closely related small-bodied and small-beaked insect-eating bird species. The authors then look at patterns of bird traits and insect numbers along other mountain ranges in tropical Ecuador, Tanzania, and New Guinea and find that patterns of bird beak size match patterns of insect size. The authors argue that resource availability likely plays an important role in shaping bird diversity patterns globally.</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;">V</span>ariation in species richness across environmental gradients results from a combination of historical non-equilibrium processes (time, speciation, extinction) and present-day differences in environmental carrying capacities (i.e., ecological limits, affected by species interactions and the abundance and diversity of resources). In a study of bird richness along the sub-tropical east Himalayan elevational gradient, we test the prediction that species richness patterns are consistent with ecological limits using data on morphology, phylogeny, elevational distribution, and arthropod resources. Species richness peaks at mid-elevations. Occupied morphological volume is roughly constant from low to mid-elevations, implying more species are packed into the same space at mid-elevations compared with low elevations. However, variance in beak length, and differences in beak length between close relatives decline with elevation, a consequence of the addition of many small insectivores at mid-elevations. These patterns are predicted from resource distributions: arthropod size diversity declines from low to mid elevations, largely because many more small insects are present at mid-elevations. Weak correlations of species mean morphological traits with elevation also match predictions based on resources and habitats. Elevational transects in the tropical Andes, New Guinea, and Tanzania similarly show declines in mean arthropod size and mean beak length, and in these cases likely contribute to declining numbers of insectivorous bird species richness along these gradients. The results imply conditions for ecological limits are met, although historical non-equilibrium processes are likely to also contribute to the pattern of species richness.</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, 19 Dec 2019 06:00:00 GMT “Flies exploit predictable perspectives and backgrounds to enhance iridescent signal salience and mating success” https://amnat.org/an/newpapers/Apr-White-A.html Thomas E. White, Nina Vogel-Ghibely, and Nathan J. Butterworth (Apr 2020) Males flies take a female’s perspective to enhance the attractiveness of their iridescent signals Read the Article (Just Accepted) Abstract Communication requires both the encoding of information and its effective transmission, but little is known about display traits that primarily serve to enhance efficacy. Here we examined the visual courtships of Lispe cana, a cursorial fly that lives and mates in heterogeneous foreshores, and tested the prediction that males should seek to enhance signal salience and consequent fitness through the flexible choice of display locations. We show that courting males access the field of view of females by straddling them and holding their wings closed, before moving ahead to present their structurally colored faces in ritualized dances. Males preferentially present these UV-white signals against darker backgrounds, and the magnitude of contrast predicts female attention, which in turn predict mating success. Our results demonstrate a striking interplay between the physical and attentional manipulation of receivers and reveal novel routes to the enhancement of signal efficacy in noisy environments. More forthcoming papers &raquo; <p>Thomas E. White, Nina Vogel-Ghibely, and Nathan J. Butterworth (Apr 2020)</p> <p><b>Males flies take a female&rsquo;s perspective to enhance the attractiveness of their iridescent signals </b></p><p><i><a href="https://dx.doi.org/10.1086/707584">Read the Article</a></i> (Just Accepted) </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;">C</span>ommunication requires both the encoding of information and its effective transmission, but little is known about display traits that primarily serve to enhance efficacy. Here we examined the visual courtships of <i>Lispe cana</i>, a cursorial fly that lives and mates in heterogeneous foreshores, and tested the prediction that males should seek to enhance signal salience and consequent fitness through the flexible choice of display locations. We show that courting males access the field of view of females by straddling them and holding their wings closed, before moving ahead to present their structurally colored faces in ritualized dances. Males preferentially present these UV-white signals against darker backgrounds, and the magnitude of contrast predicts female attention, which in turn predict mating success. Our results demonstrate a striking interplay between the physical and attentional manipulation of receivers and reveal novel routes to the enhancement of signal efficacy in noisy environments.</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, 11 Dec 2019 06:00:00 GMT “When do individuals maximize their inclusive fitness?” https://amnat.org/an/newpapers/Apr-Lehmann-A.html Laurent Lehmann and François Rousset (Apr 2020) Conjuring inclusive fitness Read the Article (Just Accepted) Abstract Adaptation is often described in behavioral ecology as individuals maximizing their inclusive fitness. Under what conditions does this hold and how does this relate to the gene-centered perspective of adaptation? We unify and extend the literature on these questions to class-structured populations. We demonstrate that the maximization (in the best-response sense) of class-specific inclusive fitness obtains in uninvadable population states (meaning that all deviating mutant go extinct). This defines a genuine actor-centered perspective on adaptation. But this inclusive fitness is assigned to all bearers of a mutant allele in a given class and depends on distributions of demographic and genetic contexts. These distributions, in turn, usually depend on events in previous generations and are thus not under individual control. This prevents, in general, from envisioning individuals themselves as autonomous fitness-maximizers, each with its own inclusive fitness. For weak selection, however, the dependence on earlier events can be neglected. We then show that each individual in each class appears to maximize its own inclusive fitness when all other individuals exhibit fitness-maximizing behavior. This defines a genuine individual-centered perspective of adaptation and justifies formally, as a first-order approximation, the long-heralded view of individuals appearing to maximize their own inclusive fitness. More forthcoming papers &raquo; <p>Laurent Lehmann and François Rousset (Apr 2020) </p> <p><b>Conjuring inclusive fitness </b></p> <p><i><a href="https://dx.doi.org/10.1086/707561">Read the Article</a></i> (Just Accepted) </p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>daptation is often described in behavioral ecology as individuals maximizing their inclusive fitness. Under what conditions does this hold and how does this relate to the gene-centered perspective of adaptation? We unify and extend the literature on these questions to class-structured populations. We demonstrate that the maximization (in the best-response sense) of class-specific inclusive fitness obtains in uninvadable population states (meaning that all deviating mutant go extinct). This defines a genuine actor-centered perspective on adaptation. But this inclusive fitness is assigned to all bearers of a mutant allele in a given class and depends on distributions of demographic and genetic contexts. These distributions, in turn, usually depend on events in previous generations and are thus not under individual control. This prevents, in general, from envisioning individuals themselves as autonomous fitness-maximizers, each with its own inclusive fitness. For weak selection, however, the dependence on earlier events can be neglected. We then show that each individual in each class appears to maximize its own inclusive fitness when all other individuals exhibit fitness-maximizing behavior. This defines a genuine individual-centered perspective of adaptation and justifies formally, as a first-order approximation, the long-heralded view of individuals appearing to maximize their own inclusive fitness. </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, 11 Dec 2019 06:00:00 GMT “Belowground competition can influence the evolution of root traits” https://amnat.org/an/newpapers/Apr-Colom.html Sara M. Colom and Regina S. Baucom (Apr 2020) Experimental evidence that belowground competition can influence the evolution of root traits! Read the Article (Just Accepted) How does belowground root-root competition influence plant diversity and evolution? Roots provide structural support and likewise play a key role in nutrient and water acquisition from the soil. Roots are also key in mediating belowground plant-plant interactions. Despite these important ecological and functional roles, however, research on if and how belowground competition may influence the evolution of root traits remains relatively uncharted territory. Research from Sara Colom and Regina Baucom in the Ecology and Evolutionary Biology Department at the University of Michigan fills this gap by addressing the potential that belowground competition acts as an agent of selection on root traits. They performed a series of greenhouse and field experiments at the Matthaei Botanical Gardens in Ann Arbor, Michigan, using two sister species of morning glories (Ipomoea purpurea and Ipomoea hederacea) as their model system. They found that belowground root phenotypes varied between species—with I.&nbsp;hederacea being wider than I.&nbsp;purpurea, and I.&nbsp;purpurea exhibiting lateral roots that are more angled toward the soil surface than I.&nbsp;hederacea—but that there was still significant phenotypic overlap between them, such that they likely compete for the same resources when growing in close proximity. They also found evidence for genetic variation underlying root traits, and that competition between the two species negatively influenced fitness in field conditions. Importantly, they found that belowground competitive interactions between the two species altered the pattern of selection on root traits differently in each: competition with I.&nbsp;purpurea changed the pattern of selection on root angle in I.&nbsp;hederacea, and competitive interactions with I.&nbsp;hederacea changed the pattern of selection on root size in I.&nbsp;purpurea. Overall, this research shows that belowground competition can have important implications on plant diversity and evolution, and highlights that research on the evolutionary ecology of root traits has long been overlooked. Abstract Although root traits play a critical role in mediating plant-plant interactions and resource acquisition from the soil environment, research examining if and how belowground competition can influence the evolution of root traits remains largely unexplored. Here we examine the potential that root traits may evolve as a target of selection from interspecific competition using Ipomoea purpurea and I&nbsp;hederacea, two closely related morning glory species that commonly co-occur in the United States as a model system. We show that belowground competitive interactions between the two species can alter the pattern of selection on root traits in each species. Specifically, competition with I&nbsp;purpurea changes the pattern of selection on root angle in I&nbsp;hederacea, and competitive interactions with I&nbsp;hederacea changes the pattern of selection on root size in I&nbsp;purpurea. However, we did not uncover evidence that intraspecific competition altered the pattern of selection on any root traits within I&nbsp;hederacea. Overall, our results suggest that belowground competition between closely related species can influence the phenotypic evolution of root traits in natural populations. Our findings provide a microevolutionary perspective of how competitive belowground interactions may impact plant fitness, potentially leading to patterns of plant community structure. More forthcoming papers &raquo; <p>Sara M. Colom and Regina S. Baucom (Apr 2020) </p> <p><b>Experimental evidence that belowground competition can influence the evolution of root traits! </b></p> <p><i><a href="https://dx.doi.org/10.1086/707597">Read the Article</a></i> (Just Accepted) </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;">H</span>ow does belowground root-root competition influence plant diversity and evolution? Roots provide structural support and likewise play a key role in nutrient and water acquisition from the soil. Roots are also key in mediating belowground plant-plant interactions. Despite these important ecological and functional roles, however, research on if and how belowground competition may influence the evolution of root traits remains relatively uncharted territory. </p><p>Research from Sara Colom and Regina Baucom in the Ecology and Evolutionary Biology Department at the University of Michigan fills this gap by addressing the potential that belowground competition acts as an agent of selection on root traits. They performed a series of greenhouse and field experiments at the Matthaei Botanical Gardens in Ann Arbor, Michigan, using two sister species of morning glories (<i>Ipomoea purpurea</i> and <i>Ipomoea hederacea</i>) as their model system. </p><p>They found that belowground root phenotypes varied between species—with <i>I.&nbsp;hederacea</i> being wider than <i>I.&nbsp;purpurea</i>, and <i>I.&nbsp;purpurea</i> exhibiting lateral roots that are more angled toward the soil surface than <i>I.&nbsp;hederacea</i>—but that there was still significant phenotypic overlap between them, such that they likely compete for the same resources when growing in close proximity. They also found evidence for genetic variation underlying root traits, and that competition between the two species negatively influenced fitness in field conditions. Importantly, they found that belowground competitive interactions between the two species altered the pattern of selection on root traits differently in each: competition with <i>I.&nbsp;purpurea</i> changed the pattern of selection on root angle in <i>I.&nbsp;hederacea</i>, and competitive interactions with <i>I.&nbsp;hederacea</i> changed the pattern of selection on root size in <i>I.&nbsp;purpurea</i>. </p><p>Overall, this research shows that belowground competition can have important implications on plant diversity and evolution, and highlights that research on the evolutionary ecology of root traits has long been overlooked. </p> <hr /><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>lthough root traits play a critical role in mediating plant-plant interactions and resource acquisition from the soil environment, research examining if and how belowground competition can influence the evolution of root traits remains largely unexplored. Here we examine the potential that root traits may evolve as a target of selection from interspecific competition using <i>Ipomoea purpurea</i> and <i>I&nbsp;hederacea</i>, two closely related morning glory species that commonly co-occur in the United States as a model system. We show that belowground competitive interactions between the two species can alter the pattern of selection on root traits in each species. Specifically, competition with <i>I&nbsp;purpurea</i> changes the pattern of selection on root angle in <i>I&nbsp;hederacea</i>, and competitive interactions with <i>I&nbsp;hederacea</i> changes the pattern of selection on root size in <i>I&nbsp;purpurea</i>. However, we did not uncover evidence that intraspecific competition altered the pattern of selection on any root traits within <i>I&nbsp;hederacea</i>. Overall, our results suggest that belowground competition between closely related species can influence the phenotypic evolution of root traits in natural populations. Our findings provide a microevolutionary perspective of how competitive belowground interactions may impact plant fitness, potentially leading to patterns of plant community structure. </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, 11 Dec 2019 06:00:00 GMT “Thermal variability and plasticity drive the outcome of a host-pathogen interaction” https://amnat.org/an/newpapers/Apr-Ferguson.html Laura Ferguson and Brent Sinclair (Apr 2020) Crickets show that predicting disease under climate change may be less complicated than we feared Read the Article (Just Accepted) It’s hard enough to predict the effects of climate change on one species, but nature is full of complicated interactions between organisms and their pathogens. Even worse, although most experiments are done under constant temperatures, we know that temperatures fluctuate in the real world. Put these together, and the future of disease in a changing world appears impossibly complicated. To explore this complexity, Dr. Laura Ferguson, then a PhD student at Western University in Canada, and her supervisor, Dr. Brent Sinclair, infected spring field crickets with a pathogenic fungus under various thermal regimes. They found that both the crickets and the fungus were sensitive to temperature, and the thermal history of each player could impact their relative success during infection. Crickets used to fluctuating temperatures were better at fighting fungi than their warm counterparts, but fungi from the cold were generally better at killing crickets. Further, when the temperature fluctuated between day and night during infection, the outcome was markedly different from infections under more artificial, constant temperature regimes. But did a simple change to a more ecologically realistic temperature pattern make it impossible to predict the outcome of an infection? Remarkably, Ferguson and Sinclair found that they could easily predict the outcome of infections under the fluctuating temperatures by averaging the number of cricket deaths under constant warm or cold temperatures. Thus, although fluctuating temperatures must be accounted for when we predict future infection dynamics, it may be possible to make these predictions using simple experiments at constant temperatures. Although we have yet to determine how generalizable this predictability might be, these results suggest that understanding how temperature affects infection dynamics and disease under climate change is within our grasp. Abstract Variable, changing, climates may affect each participant in a biotic interaction differently. We explored the effects of temperature and plasticity on the outcome of a host-pathogen interaction to try to predict the outcomes of infection under fluctuating temperatures. We infected Gryllus veletis crickets with the entomopathogenic fungus Metarhizium brunneum under constant (6°C, 12°C, 18°C or 25°C) or fluctuating temperatures (6°C to 18°C or 6°C to 25°C). We also acclimated crickets and fungi to constant or fluctuating conditions. Crickets acclimated to fluctuating conditions survived best under constant conditions if paired with warm-acclimated fungus. Overall, matches and mismatches in thermal performance, driven by acclimation, determined host survival. Mismatched performance also determined differences in survival under different fluctuating thermal regimes: crickets survived best when fluctuating temperatures favored their performance (6°C to 25°C), compared to fluctuations that favored fungus performance (6°C to 18°C). Thus, we could predict the outcome of infection under fluctuating temperatures by averaging relative host-pathogen performance under constant temperatures, suggesting that it may be possible to predict responses to fluctuating temperatures for at least some biotic interactions. More forthcoming papers &raquo; <p>Laura Ferguson and Brent Sinclair (Apr 2020) </p> <p><b>Crickets show that predicting disease under climate change may be less complicated than we feared </b></p> <p><i><a href="https://dx.doi.org/10.1086/707545">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">I</span>t’s hard enough to predict the effects of climate change on one species, but nature is full of complicated interactions between organisms and their pathogens. Even worse, although most experiments are done under constant temperatures, we know that temperatures fluctuate in the real world. Put these together, and the future of disease in a changing world appears impossibly complicated. To explore this complexity, Dr. Laura Ferguson, then a PhD student at Western University in Canada, and her supervisor, Dr. Brent Sinclair, infected spring field crickets with a pathogenic fungus under various thermal regimes. They found that both the crickets and the fungus were sensitive to temperature, and the thermal history of each player could impact their relative success during infection. Crickets used to fluctuating temperatures were better at fighting fungi than their warm counterparts, but fungi from the cold were generally better at killing crickets. Further, when the temperature fluctuated between day and night during infection, the outcome was markedly different from infections under more artificial, constant temperature regimes. But did a simple change to a more ecologically realistic temperature pattern make it impossible to predict the outcome of an infection? Remarkably, Ferguson and Sinclair found that they could easily predict the outcome of infections under the fluctuating temperatures by averaging the number of cricket deaths under constant warm or cold temperatures. Thus, although fluctuating temperatures must be accounted for when we predict future infection dynamics, it may be possible to make these predictions using simple experiments at constant temperatures. Although we have yet to determine how generalizable this predictability might be, these results suggest that understanding how temperature affects infection dynamics and disease under climate change is within our grasp. </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;">V</span>ariable, changing, climates may affect each participant in a biotic interaction differently. We explored the effects of temperature and plasticity on the outcome of a host-pathogen interaction to try to predict the outcomes of infection under fluctuating temperatures. We infected <i>Gryllus veletis</i> crickets with the entomopathogenic fungus <i>Metarhizium brunneum</i> under constant (6°C, 12°C, 18°C or 25°C) or fluctuating temperatures (6°C to 18°C or 6°C to 25°C). We also acclimated crickets and fungi to constant or fluctuating conditions. Crickets acclimated to fluctuating conditions survived best under constant conditions if paired with warm-acclimated fungus. Overall, matches and mismatches in thermal performance, driven by acclimation, determined host survival. Mismatched performance also determined differences in survival under different fluctuating thermal regimes: crickets survived best when fluctuating temperatures favored their performance (6°C to 25°C), compared to fluctuations that favored fungus performance (6°C to 18°C). Thus, we could predict the outcome of infection under fluctuating temperatures by averaging relative host-pathogen performance under constant temperatures, suggesting that it may be possible to predict responses to fluctuating temperatures for at least some biotic 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, 05 Dec 2019 06:00:00 GMT “Safety cues can give prey more valuable information than danger cues” https://amnat.org/an/newpapers/Apr-Luttbeg.html Barney Luttbeg, Maud C. O. Ferrari, Daniel T. Blumstein, and Douglas P. Chivers (Apr 2020) Prey fitness increased by safety cues (precise information at low risk levels) over danger cues (precise at high risk) Read the Article (Just Accepted) Prey fear of predators shaping ecological communities has become a widespread perspective for ecologists. The primary story has been that prey forage and do other kinds of risky behaviors until they receive a cue that indicates that a predator is currently nearby or about to attack. This view has emphasized how risk and fear shapes the behaviors of prey and ecological dynamics. But what if there are cues that are more effective at indicating low levels of predation risk? Would prey benefit more from these safety cues than from danger cues that are effective at indicating high levels of predation risk? Scientists from Oklahoma State University, the University of Saskatchewan, and the University of California at Los Angeles answer these questions using computer models. They find that when prey pay more attention to safety cues than to the danger cues they are more successful at avoiding predators and finding food. This happens because safety cues provide prey with precise information about low predation risk levels where they should should be varying how intensely they forage. Danger cues, however, often provide precise information about high levels of predation risk where they should be hiding from predators. These results may begin a shift from only thinking about how fear shapes ecology to also thinking about how indications of safety shape prey behavior, physiology, and ecological dynamics. Abstract The ability of prey to assess predation risk is fundamental to their success. It is routinely assumed predator cues do not vary in reliability across levels of predation risk. We propose that cues can differ in how precisely they indicate different levels of predation risk. What we call danger cues precisely indicate high risk levels, while safety cues precisely indicate low risk levels. Using optimality modeling, we find that prey fitness is increased when prey pay more attention to safety cues than danger cues. This fitness advantage is greatest when prey need to protect assets, predators are more dangerous, and predation risk increases at an accelerating rate with prey foraging efforts. Each of these conditions lead to prey foraging less when estimated predation risk is higher. Danger cues have less value than safety cues because they give precise information about risk when it is high, but prey behavior varies little when risk is high. Safety cues give precise information about levels of risk where prey behavior varies. These results highlight how our fascination with predators may have biased the way we study predator-prey interactions and focused too exclusively on cues that clearly indicate the presence of predator rather than cues that clearly indicate their absence. More forthcoming papers &raquo; <p>Barney Luttbeg, Maud C. O. Ferrari, Daniel T. Blumstein, and Douglas P. Chivers (Apr 2020) </p> <p><b>Prey fitness increased by safety cues (precise information at low risk levels) over danger cues (precise at high risk) </b></p> <p><i><a href="https://dx.doi.org/10.1086/707544">Read the Article</a></i> (Just Accepted) </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>rey fear of predators shaping ecological communities has become a widespread perspective for ecologists. The primary story has been that prey forage and do other kinds of risky behaviors until they receive a cue that indicates that a predator is currently nearby or about to attack. This view has emphasized how risk and fear shapes the behaviors of prey and ecological dynamics. But what if there are cues that are more effective at indicating low levels of predation risk? Would prey benefit more from these safety cues than from danger cues that are effective at indicating high levels of predation risk? </p><p>Scientists from Oklahoma State University, the University of Saskatchewan, and the University of California at Los Angeles answer these questions using computer models. They find that when prey pay more attention to safety cues than to the danger cues they are more successful at avoiding predators and finding food. This happens because safety cues provide prey with precise information about low predation risk levels where they should should be varying how intensely they forage. Danger cues, however, often provide precise information about high levels of predation risk where they should be hiding from predators. These results may begin a shift from only thinking about how fear shapes ecology to also thinking about how indications of safety shape prey behavior, physiology, and ecological dynamics. </p> <hr /> <h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he ability of prey to assess predation risk is fundamental to their success. It is routinely assumed predator cues do not vary in reliability across levels of predation risk. We propose that cues can differ in how precisely they indicate different levels of predation risk. What we call danger cues precisely indicate high risk levels, while safety cues precisely indicate low risk levels. Using optimality modeling, we find that prey fitness is increased when prey pay more attention to safety cues than danger cues. This fitness advantage is greatest when prey need to protect assets, predators are more dangerous, and predation risk increases at an accelerating rate with prey foraging efforts. Each of these conditions lead to prey foraging less when estimated predation risk is higher. Danger cues have less value than safety cues because they give precise information about risk when it is high, but prey behavior varies little when risk is high. Safety cues give precise information about levels of risk where prey behavior varies. These results highlight how our fascination with predators may have biased the way we study predator-prey interactions and focused too exclusively on cues that clearly indicate the presence of predator rather than cues that clearly indicate their absence. </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, 05 Dec 2019 06:00:00 GMT “Reinforcement learning theory reveals the cognitive requirements for solving the cleaner fish market task” https://amnat.org/an/newpapers/Apr-Quinones.html Andrés E. Quiñones, Arnon Lotem, Olof Leimar, and Redouan Bshary (Apr 2020) Reinforcement learning theory unveils the cognitive mechanisms cleaner fish use to deal with their social environment Read the Article (Just Accepted) The cleaner fish Labroides dimidiatus fulfils the important task of ridding other coral reef fish of parasites. The demand for cleaning services can be so high that often cleaners will have to choose between several potential clients who seek service at the same time. Experimental work carried on the Lizard Island research station, at the Great Barrier Reef, shows that some cleaners can be strategic when making these decisions. They more often prioritize clients that, due to large range sizes, can switch to a different cleaner if not immediately served. Cleaners using this strategy get access to both impatient and patient clients, and hence more food. This strategic decision-making is, however, not innate. Juveniles, and some adults, do not prefer clients with more leverage in the economic transaction. Why, then, do some cleaners fail at learning the more profitable preference? Using a computational model based on the building blocks of machine learning algorithms, Quiñones and collaborators show that cleaners need two important adaptations in the learning process. First, they need to account for the future effect of their choices whilst making decisions. That is because the extra food will come much later than their decision of whom to clean first. Second, they must be able to develop different preferences for a client type, depending on which other client is available. A particular client type should only get priority when it is together with another type, which has less access to alternative cleaners. This boils down to making decisions according to the context in which they are made. Interestingly, in the past, researchers considered these two cognitive adaptations to be exclusively human, as they are involved in human cognitive processes such as language acquisition. This opens up the question of whether these seemingly similar processes are implemented in comparable ways. Abstract Learning is an adaptation that allows individuals to respond to environmental stimuli in ways that improve their reproductive outcomes. The degree of sophistication in learning mechanisms potentially explains variation in behavioral responses. Here, we present a model of learning that is inspired by documented intra- and interspecific variation in the performance in a simultaneous two-choice task, the ‘biological market task’. The task presents a problem that cleaner fish often face in nature: the decision of choosing between two client types; one that is willing to wait for inspection and one that may leave if ignored. The cleaners’ choice hence influences the future availability of clients, i.e. it influences food availability. We show that learning the preference that maximizes food intake requires subjects to represent in their memory different combinations of pairs of client types rather than just individual client types. In addition, subjects need to account for future consequences of actions, either by estimating expected long-term reward or by experiencing a client leaving as a penalty (negative reward). Finally, learning is influenced by the absolute and relative abundance of client types. Thus, cognitive mechanisms and ecological conditions jointly explain intra and interspecific variation in the ability to learn the adaptive response. More forthcoming papers &raquo; <p>Andrés E. Quiñones, Arnon Lotem, Olof Leimar, and Redouan Bshary (Apr 2020) </p> <p><b>Reinforcement learning theory unveils the cognitive mechanisms cleaner fish use to deal with their social environment </b></p> <p><i><a href="https://dx.doi.org/10.1086/707519">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">T</span>he cleaner fish <i>Labroides dimidiatus</i> fulfils the important task of ridding other coral reef fish of parasites. The demand for cleaning services can be so high that often cleaners will have to choose between several potential clients who seek service at the same time. Experimental work carried on the Lizard Island research station, at the Great Barrier Reef, shows that some cleaners can be strategic when making these decisions. They more often prioritize clients that, due to large range sizes, can switch to a different cleaner if not immediately served. Cleaners using this strategy get access to both impatient and patient clients, and hence more food. This strategic decision-making is, however, not innate. Juveniles, and some adults, do not prefer clients with more leverage in the economic transaction. Why, then, do some cleaners fail at learning the more profitable preference? Using a computational model based on the building blocks of machine learning algorithms, Quiñones and collaborators show that cleaners need two important adaptations in the learning process. First, they need to account for the future effect of their choices whilst making decisions. That is because the extra food will come much later than their decision of whom to clean first. Second, they must be able to develop different preferences for a client type, depending on which other client is available. A particular client type should only get priority when it is together with another type, which has less access to alternative cleaners. This boils down to making decisions according to the context in which they are made. Interestingly, in the past, researchers considered these two cognitive adaptations to be exclusively human, as they are involved in human cognitive processes such as language acquisition. This opens up the question of whether these seemingly similar processes are implemented in comparable ways. </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;">L</span>earning is an adaptation that allows individuals to respond to environmental stimuli in ways that improve their reproductive outcomes. The degree of sophistication in learning mechanisms potentially explains variation in behavioral responses. Here, we present a model of learning that is inspired by documented intra- and interspecific variation in the performance in a simultaneous two-choice task, the ‘biological market task’. The task presents a problem that cleaner fish often face in nature: the decision of choosing between two client types; one that is willing to wait for inspection and one that may leave if ignored. The cleaners’ choice hence influences the future availability of clients, i.e. it influences food availability. We show that learning the preference that maximizes food intake requires subjects to represent in their memory different combinations of pairs of client types rather than just individual client types. In addition, subjects need to account for future consequences of actions, either by estimating expected long-term reward or by experiencing a client leaving as a penalty (negative reward). Finally, learning is influenced by the absolute and relative abundance of client types. Thus, cognitive mechanisms and ecological conditions jointly explain intra and interspecific variation in the ability to learn the adaptive response. </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, 04 Dec 2019 06:00:00 GMT “Adaptive maternal investment in the wild? Links between maternal growth trajectory and offspring size, growth, and survival in contrasting environments” https://amnat.org/an/newpapers/Apr-Burton.html Tim Burton, Njal Rollinson, Simon McKelvey, David C. Stewart, John D. Armstrong, and Neil B. Metcalfe (Apr 2020) Maternal growth trajectory influences offspring growth & survival independently of variation in initial offspring size Read the Article (Just Accepted) Mothers often choose between producing many young that are small or fewer young that are large. In addition to this trade-off between offspring ‘quantity and quality’, recent studies have shown that mothers influence additional traits of their young, e.g. their behavior or rate of growth, and can use their own experience as juveniles to inform this decision. This is expected to occur in species where the environment experienced by mothers when they were juveniles can reliably ‘predict’ the type of environment to be faced by their developing young. Atlantic salmon may be a species where such cross-generational phenomena occur, because females home with great accuracy to spawn their eggs in nests, hidden in the gravel of the very same freshwater streams where they grew up themselves. Researchers from the University of Glasgow, University of Toronto, and Marine Scotland manipulated nutrient levels (and thus productivity) in tributary streams of the River Conon in north Scotland to investigate if female salmon who grew slowly when they were young (and thus likely experienced a unproductive nursery environment) would produce young ‘tailored’ to such conditions themselves. The young of slower-growing mothers were larger and grew more slowly than those of faster-growing mothers, irrespective of stream nutrient levels. However, the young of slow-growing mothers had higher survival prospects in streams where the density of predatory brown trout was high. Intriguingly, these links between growth trajectory of the mother and the survival of her young occurred independently of differences in the initial size of eggs from which these juveniles hatched. This suggests that female salmon may also be adjusting aspects of their young other than their size to better prepare them for the environment they will face in early life. Abstract Life history theory predicts that investment per offspring should correlate negatively with the quality of environment offspring are anticipated to encounter; parents may use their own experience as juveniles to predict this environment and may modulate offspring traits such as growth capacity as well as initial size. We manipulated nutrient levels in the juvenile habitat of wild Atlantic salmon Salmo salar to investigate the hypothesis that the egg size maximizing juvenile growth and survival depends on environmental quality. We also tested whether offspring traits were related to parental growth trajectory. Mothers that grew fast when young produced more, smaller offspring than mothers that had grown slowly to reach the same size. Despite their size disadvantage, offspring of faster-growing mothers grew faster than those of slow-growing mothers in all environments, counter to the expectation that they would be competitively disadvantaged. However, they had lower relative survival in environments where the density of older predatory/competitor fish was relatively high. These links between maternal (but not paternal) growth trajectory and offspring survival rate were independent of egg size, underscoring that mothers may be adjusting egg traits other than size to suit the anticipated environment faced by their offspring. More forthcoming papers &raquo; <p>Tim Burton, Njal Rollinson, Simon McKelvey, David C. Stewart, John D. Armstrong, and Neil B. Metcalfe (Apr 2020) </p> <p><b>Maternal growth trajectory influences offspring growth & survival independently of variation in initial offspring size </b></p> <p><i><a href="https://dx.doi.org/10.1086/707518">Read the Article</a></i> (Just Accepted) </p><p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">M</span>others often choose between producing many young that are small or fewer young that are large. In addition to this trade-off between offspring ‘quantity and quality’, recent studies have shown that mothers influence additional traits of their young, e.g. their behavior or rate of growth, and can use their own experience as juveniles to inform this decision. This is expected to occur in species where the environment experienced by mothers when they were juveniles can reliably ‘predict’ the type of environment to be faced by their developing young. Atlantic salmon may be a species where such cross-generational phenomena occur, because females home with great accuracy to spawn their eggs in nests, hidden in the gravel of the very same freshwater streams where they grew up themselves. Researchers from the University of Glasgow, University of Toronto, and Marine Scotland manipulated nutrient levels (and thus productivity) in tributary streams of the River Conon in north Scotland to investigate if female salmon who grew slowly when they were young (and thus likely experienced a unproductive nursery environment) would produce young ‘tailored’ to such conditions themselves. The young of slower-growing mothers were larger and grew more slowly than those of faster-growing mothers, irrespective of stream nutrient levels. However, the young of slow-growing mothers had higher survival prospects in streams where the density of predatory brown trout was high. Intriguingly, these links between growth trajectory of the mother and the survival of her young occurred independently of differences in the initial size of eggs from which these juveniles hatched. This suggests that female salmon may also be adjusting aspects of their young other than their size to better prepare them for the environment they will face in early life.</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;">L</span>ife history theory predicts that investment per offspring should correlate negatively with the quality of environment offspring are anticipated to encounter; parents may use their own experience as juveniles to predict this environment and may modulate offspring traits such as growth capacity as well as initial size. We manipulated nutrient levels in the juvenile habitat of wild Atlantic salmon <i>Salmo salar</i> to investigate the hypothesis that the egg size maximizing juvenile growth and survival depends on environmental quality. We also tested whether offspring traits were related to parental growth trajectory. Mothers that grew fast when young produced more, smaller offspring than mothers that had grown slowly to reach the same size. Despite their size disadvantage, offspring of faster-growing mothers grew faster than those of slow-growing mothers in all environments, counter to the expectation that they would be competitively disadvantaged. However, they had lower relative survival in environments where the density of older predatory/competitor fish was relatively high. These links between maternal (but not paternal) growth trajectory and offspring survival rate were independent of egg size, underscoring that mothers may be adjusting egg traits other than size to suit the anticipated environment faced by their offspring. </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, 04 Dec 2019 06:00:00 GMT “An empirical test of the role of small-scale transmission in large-scale disease dynamics” https://amnat.org/an/newpapers/Apr-Mihaljevic-A.html Joseph R. Mihaljevic, Carlos M. Polivka, Constance J. Mehmel, Chentong Li, Vanja Dukic, and Greg Dwyer (Apr 2020) Study shows that small-scale transmission dynamics are insufficient to explain large-scale patterns of disease incidence Read the Article (Just Accepted) Abstract A&nbsp;key assumption of epidemiological models is that population-scale disease spread is driven by close contact between hosts and pathogens. At larger scales, however, mechanisms such as spatial structure in host and pathogen populations and environmental heterogeneity could alter disease spread. The assumption that small-scale transmission mechanisms are sufficient to explain large-scale infection rates, however, is rarely tested. Here we provide a rigorous test using an insect-baculovirus system. We fit a mathematical model to data from forest-wide epizootics, while constraining the model parameters with data from branch-scale experiments, a difference in spatial scale of four orders of magnitude. This experimentally-constrained model fits the epizootic data well, supporting the role of small-scale transmission, but variability is high. We then compare this model’s performance to an unconstrained model that ignores the experimental data, which serves as a proxy for models with additional mechanisms. The unconstrained model has a superior fit, revealing a higher transmission rate across forests compared to branch-scale estimates. Our study suggests that small-scale transmission is insufficient to explain baculovirus epizootics. Further research is needed to identify the mechanisms that contribute to disease spread across large spatial scales, and synthesizing models and multi-scale data is key to understanding these dynamics. More forthcoming papers &raquo; <p>Joseph R. Mihaljevic, Carlos M. Polivka, Constance J. Mehmel, Chentong Li, Vanja Dukic, and Greg Dwyer (Apr 2020) </p> <p><b>Study shows that small-scale transmission dynamics are insufficient to explain large-scale patterns of disease incidence </b></p> <p><i><a href="https://dx.doi.org/10.1086/707457">Read the Article</a></i> (Just Accepted) </p><h3>Abstract</h3> <p><span style="float: left; font-size: 40px; line-height: 25px; padding-top: 4px; padding-right: 2px; padding-left: 2px; font-family: Garamond; font-weight: bold;">A</span>&nbsp;key assumption of epidemiological models is that population-scale disease spread is driven by close contact between hosts and pathogens. At larger scales, however, mechanisms such as spatial structure in host and pathogen populations and environmental heterogeneity could alter disease spread. The assumption that small-scale transmission mechanisms are sufficient to explain large-scale infection rates, however, is rarely tested. Here we provide a rigorous test using an insect-baculovirus system. We fit a mathematical model to data from forest-wide epizootics, while constraining the model parameters with data from branch-scale experiments, a difference in spatial scale of four orders of magnitude. This experimentally-constrained model fits the epizootic data well, supporting the role of small-scale transmission, but variability is high. We then compare this model’s performance to an unconstrained model that ignores the experimental data, which serves as a proxy for models with additional mechanisms. The unconstrained model has a superior fit, revealing a higher transmission rate across forests compared to branch-scale estimates. Our study suggests that small-scale transmission is insufficient to explain baculovirus epizootics. Further research is needed to identify the mechanisms that contribute to disease spread across large spatial scales, and synthesizing models and multi-scale data is key to understanding these dynamics. </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, 26 Nov 2019 06:00:00 GMT