ASN RSS

"The Effect of Brief or Prolonged Bouts of Winning or Losing Male-Male Contests on Plasticity in Sexually Selected Traits"

Mon, 29 May 2023 05:00:00 GMT

Lauren M. Harrison, Regina Vega-Trejo, and Michael D. Jennions, March 2023

Males compete with other males for access to reproduce with females. Depending on the species, this competition can include fighting for access to potential mates, such as horn-based combat in rhinoceros beetles, or investing in courtship or attractive ornaments, such as the ornate bowers of bowerbirds or the ostentatious tail feathers of peacocks. But if females mate with multiple males, the competition can continue inside her reproductive tract after males successfully mate. As a result, having faster sperm or more sperm can improve a male’s likelihood of siring offspring. Can the outcome of a contest change how males invest in these reproductive traits?

In this study, researchers from Australian National University and Oxford University examined whether repeatedly winning or losing aggressive contests changed how males then invested in traits that would maximise his chances of producing offspring – fighting if he is a winner, or sperm competitiveness if he is a loser. Male mosquitofish (Gambusia holbrooki) are quite aggressive toward each other, with fights escalating from a circling display to fin nipping to chasing. In this study, the authors gave male mosquitofish the experience of repeatedly winning or losing contests by housing them in a tank with a rotating set of larger or smaller competitor males for 1 day, 1 week, or 3 weeks. During this time, fish were able to compete freely. Then, they put one winning male and one losing male from a given time treatment in a tank with a female and measured how the males’ social experience altered their investment in pre-copulatory and post-copulatory traits.

The researchers found that winners (fish that were paired with smaller males) invested more than losers in behaviors related to mate acquisition, including mating attempts and time spent near females. Surprisingly, males who experienced one day of winning showed the same response as males who experienced three weeks of winning, suggesting that males can alter their mating behavior immediately in response to social experience. However, there was no difference in the males’ post-mating investment, including sperm counts and swimming speed. This might mean that sperm traits are less responsive to immediate social experience than behavioral traits.

These results show that males respond to their competitive environment by changing how much they invest in acquiring a mate, but not necessarily how much they invest in fertilization success. However, the researchers found another interesting pattern: the size of the focal male actually changes how much they invest in mate acquisition in response to winning or losing. Small males that won ended up spending even more time associating with the female than their larger counterparts. This could be because smaller males typically lose fights, and the unexpected experience of winning could signal a noticeable change in status. This study shows that the benefit a male gets from investing in mate acquisition can partly depend on his body size. But regardless of body size or fighting ability, winning a competition can have a significant impact on how males invest in mate acquisition. This is particularly exciting, because it demonstrates that a male’s social experience with other males can transform how he interacts with females, showing how intrasexual selection can influence intersexual selection.

Abstract

Fight outcomes often affect male fitness by determining their access to mates. Thus, “winner-loser” effects, where winners often win their next contest while losers tend to lose, can influence how males allocate resources toward pre- and postcopulatory traits. We experimentally manipulated the winning/losing experiences of pairs of size-matched male Gambusia holbrooki for 1 day, 1 week, or 3 weeks to test whether prior winning/losing experiences differentially affect the plasticity of male investment into either mating effort (precopulatory) or ejaculates (postcopulatory). When winner/loser pairs directly competed for a female, winners had better precopulatory outcomes than losers for three of the four traits we measured: mating attempts, successful attempts, and time spent with the female (but not aggression). However, winners and losers did not differ in either total sperm counts or sperm velocity. Interestingly, absolute male size, an important predictor of fighting success, mediated winner-loser effects on how long males then spent near a female. Compared with losers, smaller winners spent more time with the female than did larger winners, suggesting that how males respond to prior social experiences is size dependent. We discuss the general importance of controlling for inherent male condition when comparing male investment into condition-dependent traits.

Author Bio:

Clara Stahlmann Roeder is a PhD student at the University of Virginia studying the evolution of social behavior. She uses male-male contests in forked fungus beetles to investigate how age and social experience shape social interactions. When she's not setting up battle arenas, she is likely cooking, swing dancing, or going on bird walks.

2023 ASN Award for Distinguished Achievement in the Conceptual Unification of the Biological Sciences

Thu, 25 May 2023 05:00:00 GMT

Within community ecology, interactions in which both partners benefit from the interaction—mutualisms—are ubiquitous. Historically, however, species interactions were generally considered antagonistic, and many investigators ignored the possibility of a role for mutualisms in biological communities. Dr. Judith L. Bronstein has devoted her career to simultaneously exploring the breadth and intricacies of numerous types of mutualistic interactions and highlighting the critical roles that various mutualistic species interactions play in structuring biological communities to remedy this fundamental shortcoming in how we conceptualize the natural world.

Dr. Bronstein began her scientific career studying the iconic mutualism between figs (Ficus species) and their specialist pollinators, the agaonid fig wasps. Figs are pollinated by female fig wasps. However, the female wasps also oviposit only on ovaries in the pollinated flower, and the developing offspring consume the ovaries they occupy. This interaction starkly showcases a contradiction that is inherent in most mutualisms, that one or both interacting species pay some fitness costs in gaining the benefits of the interaction. For a fig tree, production of viable offspring because of the pollination services of fig wasp females entails the sacrifice of some ovaries to the wasps. Moreover, these interactions are not always beneficial, but rather shift between mutualism and antagonism depending on the ecological context in which the interaction occurs, and so can shift over time within the same community. Dr. Bronstein’s work is the exemplar of the rich complexity that must be considered in exploring the structure and dynamics of mutualisms.

Throughout her career, Dr. Bronstein’s empirical work has been rooted in the natural history of the interacting species under study, and she has used that natural history to frame critical tests of hypotheses that broadly inform larger conceptual issues. In addition to the fig/fig wasp interaction, she has studied other iconic mutualisms, including yuccas and their moth pollinators, ant-plant protection mutualisms, and various nectar feeding pollinator-plant interactions. Her empirical work has also framed these interactions in broader ecological and evolutionary contexts by exploring how other species (e.g., nectar robbers, herbivores, seed predators) influence the outcomes of interactions between plants and their pollinators, how mutualisms influence the overall population dynamics of the interacting species, competition among various mutualist partners, the role of individual variation in shaping costs and benefits for partners, the consequences of various life histories of pollinators to plant fitness components, the ecological and evolutionary consequences of cheaters in these interactions, and how various mutualisms may shape the responses of species to climate change. As this recitation highlights, her empirical work has integrated perspectives across many levels of biological organization, with mutualisms being the central focus.

In parallel with her empirical work, Dr. Bronstein has also augmented the conceptual framework for mutualistic interaction, which she has advanced in two forms. One is the formulation of mechanistic models of species interactions that have explored various ecological and evolutionary roles for mutualisms, including the ecological dynamics of multiple mutualists and cheaters, species coexistence, and the coevolution of mutualist partners and how ecological and evolutionary responses to antagonistic interactions with other species influence coevolution. The other is the publication of numerous conceptual reflections and reviews that have fundamentally reshaped how ecologists and evolutionary biologists think about mutualisms, and have placed mutualisms in a more rigorous context beside other types of species’ interactions. Her 1994 review paper in the Quarterly Review of Biology was instrumental in shifting the focus of ecologists toward the study of positive species interactions and away from exclusive emphasis on negative species interactions. A central tenet of this conceptual unification is the realization that most mutualisms are actually complex consumer-resource interactions in which the benefits for one or both species being consumed frequently outweigh the costs.

Dr. Bronstein has also contributed to the conceptual unification of the biological sciences through her dedicated service to the American Society of Naturalists. She has served as an officer at all ranks within the society. Most importantly, she served as Editor and then Editor-in-Chief of The American Naturalist. In addition, she is a Fellow of the Ecological Society of America and has received a distinguished service award from NSF and distinguished teaching Awards from the University of Arizona. She has also served the ecological and evolutionary committee through editorial positions with the Annual Review of Ecology and Evolution, the Quarterly Review of Biology, and Ecology, and as a Program Director and frequent panel member at NSF. Finally, she is a member of Board of Trustees and Executive Council and Designer of science exhibits at the Sonora Desert Museum, Tucson.

Based on her record of accomplishment in both empirical and theoretical studies of mutualisms and her service to the scientific community, the American Society of Naturalists is proud to award Dr. Bronstein with the 2023 ASN Award for Distinguished Achievement in the Conceptual Unification of the Biological Sciences.

—The Committee, Ellen Ketterson, chair, Ruth Shaw, and Mark Urban with major input from Mark McPeek and Monica Geber

2023 ASN Early Career Investigator Awards

Fri, 12 May 2023 05:00:00 GMT

The American Society of Naturalist’s Early Career Investigator Award was first established in honor of Jasper Loftus-Hills, a young scientist who died tragically 3 years after receiving his PhD. This award goes to applicants who completed their PhD three years preceding the application deadline or are in their last year of a PhD program.

We are pleased to announce that this year’s recipients of the ASN Early Career Investigator Awards are Julia Kreiner, Heng Huang, Thomas Scott, and Dakota McCoy!

We are very much looking forward to their participation in the ASN Early Career Investigator symposium at the annual meeting in Albuquerque, New Mexico, this June.

2023 ASN Distinguished Naturalist Award

Fri, 12 May 2023 05:00:00 GMT

The Distinguished Naturalist Award of the American Society of Naturalists is given annually to an active midcareer scientist who has contributed significantly to the knowledge of a particular ecosystem or group of organisms and who, through this work, has illuminated key principles of evolutionary biology and an enhanced appreciation of natural history. The winner of the ASN Distinguished Naturalist Award in 2023 is Daniel Bolnick, Professor at the University of Connecticut.

Professor Bolnick has conducted influential research at the intersection of ecology and evolution, making significant contributions with both theoretical and empirical studies. His detailed work on the three-spine stickleback has greatly enriched our understanding of the natural history of that model species. Much of his research concerns the maintenance and consequences of within-species trait variation, including the mechanisms of disruptive selection, negative frequency-dependence, and the role of rarity in promoting disruptive selection throughout the animal kingdom.

Another foundational contribution involves the phenomenon of parallel evolution, again exploiting sticklebacks as a model system. Using an array of genetic and statistical techniques, Bolnick and his colleagues studied phenotypic traits and genomic data in replicate pairs of lake and stream sticklebacks to demonstrate that the widely accepted view of stickleback evolution as highly parallel is incorrect. This research has yielded a more rigorous definition of parallel evolution for any species and statistical measures to quantify it.

Bolnick’s field research on a pair of stickleback populations in a lake and an adjacent stream led to yet another line of research on the generation, maintenance, and consequences of intraspecific variation. The finding that individuals from lake and stream populations prefer to settle in their respective habitats led to further studies on the mechanistic basis for this genotype-specific behavior, as well as to a theory of adaptation via genotype-dependent-dispersal. This research counters the widely held view that gene flow is necessarily a maladaptive force acting against natural selection.

Focusing on within-species variation in stickleback diet, Bolnick’s laboratory studied the effect of this variation on the gut microbiome, including differential infection rates of intestinal parasites. Differential infection implies variable selection on immunity and tolerance, and Bolnick’s group has elucidated the costs and benefits that generate variation in immunity among stickleback populations.

Daniel Bolnick, through a combination of natural history, field and laboratory experiments, statistical explorations, and theoretical models, has produced a large and expanding body of research that informs evolution and ecology. His contributions clearly merit the Distinguished Naturalist Award.

2023 ASN Presidential Award

Thu, 11 May 2023 05:00:00 GMT

The winner of the 2023 ASN Presidential Award, chosen from among all of the papers published in the American Naturalist in 2022, is “Multituberculate Mammals Show Evidence of a Life History Strategy Similar to That of Placentals, Not Marsupials” by Lucas Weaver, Henry Fulghum, David Grossnickle, William Brightly, Zoe Kulik, Gregory Wilson Mantilla, and Megan Whitney. This paper skillfully weaves together multiple lines of inference to inform an important question in the evolutionary history of placental mammals: Did their life history enable their evolutionary success?

The placental life history strategy of having a long gestation period and relatively precocial young has been thought to be an evolutionary innovation that was critical in allowing the eventual predominance of placentals among mammalian taxa. Although this view has been challenged by some recent lines of evidence suggesting that the marsupial life history strategy of long lactation periods may be derived rather than ancestral, the question still remains open. Fossils from ancestral therian groups could lend evidence to this debate, but the life history of such groups was unknown. In this impressive study, Weaver et al. were able to infer the life history of the multituberculates, a highly successful clade of early mammals which had radiated broadly long before placentals, but which went extinct in the latter part of the Eocene.

To make this inference, Weaver et al. first explored the bone histology of placentals versus marsupials, convincingly showing that there were both diagnostic proportions of layers of different types of bone that tended to differentiate these groups and a robust relationship between the proportion of one particular type of bone and weaning age. By comparing placental and marsupial bone cross-sections to those of multituberculates, Weaver et al. were then able to infer that multituberculates shared a placental-like life history. The ancestral placement of multituberculates to the clade including placentals and marsupials lends additional support to the possibility that the marsupial life history strategy is the derived one. It also makes it clear that the placental life history strategy was not exceptional, and cannot explain the success of placentals over multituberculates in mammalian evolutionary history. This impactful work is an excellent exemplar of the more evolutionary side of The American Naturalist, integrating multiple techniques and lines of evidence, from histology to life history to phylogeny.

“Nutrigonometry I: Using Right-Angle Triangles to Quantify Nutritional Trade-Offs in Performance Landscapes”

Thu, 04 May 2023 05:00:00 GMT

Juliano Morimoto, Pedro Conceição, Christen Mirth, and Mathieu Lihoreau, May 2023

Read the Article

Pythagoras was a key figure for mathematics, discovering what's now a cornerstone theorem used across many fields. In this paper, Pythagoras reaches out to nutrition, and help us reveal the best and the worst diets.

What tools do we have to understand the evolution of animal feeding behavior? A new study by Dr. Morimoto and colleagues is providing a new model for measuring nutritional trade-offs. The model is called Nutrigonometry and uses right-angle triangles to identify optimal feeding strategies in complicated nutritional space. It promises to be an easy-to-use model that can be applied to many kinds of diet data and will help biologists untangle the complicated nutrition landscape that animals navigate throughout their lives.

It is not uncommon for animals to have traits that have different nutritional requirements, such as reproduction requiring different amounts of protein and carbohydrates compared with the immune system. Nutritional requirements can also change throughout the lifetime of an animal as they mature and grow. A mismatch in nutritional requirements can lead to what is called a nutritional trade-off and can lead to feeding behavior that favors one trait over another. An example of an already identified nutritional trade-off is between life span and reproduction in Drosophila melanogaster. D. melanogaster females will eat foods that maximize life-time egg production instead of life span. Even though many nutritional trade-offs have been identified and described, current tools make it difficult to compare results between studies or between different diet data structures. Dr. Morimoto and colleagues realized that having better tools to quantify these trade-offs will ultimately open the door for better comparison within the field of nutritional ecology and increase our understanding of behavioral evolution.

Dr Morimoto and colleagues propose using Nutrigonometry as a solution to the many problems that arise when studying multidimensional nutritional space. The framework is simple and effective at identifying previously described nutritional trade-offs, such as the one identified in Drosophila melanogaster. The framework allows for the use of many commonly used statistical tools, such as linear regressions, to identify peaks (or valleys) in the nutritional space. This means that the model can compare the optimum balance and quantity of nutrients that animals have to eat in order to maximise (peaks) or minimize (valleys) a given life-history trait, say, lifespan or reproduction. In the past this was often done visually or with highly computationally intensive tools. They show in their study that simple linear regressions combined with the Nutrigonometry framework perform better at predicting optimal regions in multidimensional nutritional space than other methods, such as machine learning. Their finding is exciting because it shows that large scale comparative studies can now be done easily. They are hoping their tool will allow future work to dive deeper into the relationship between animal foraging decisions and fitness. Ultimately, understanding the role of nutrition in physiology, behavior, and ecology will further rely on larger comparative studies and having a simple tool like Nutrigonometry will make it all the more possible.

Abstract

Animals regulate their food intake to maximize the expression of fitness traits but are forced to trade off the optimal expression of some fitness traits because of differences in the nutrient requirements of each trait (“nutritional trade-offs”). Nutritional trade-offs have been experimentally uncovered using the geometric framework for nutrition (GF). However, current analytical methods to measure such responses rely on either visual inspection or complex models of vector calculations applied to multidimensional performance landscapes, making these approaches subjective or conceptually difficult, computationally expensive, and, in some cases, inaccurate. Here, we present a simple trigonometric model to measure nutritional trade-offs in multidimensional landscapes (nutrigonometry) that relies on the trigonometric relationships of right-angle triangles and thus is both conceptually and computationally easier to understand and use than previous quantitative approaches. We applied nutrigonometry to a landmark GF data set for comparison of several standard statistical models to assess model performance in finding regions in the performance landscapes. This revealed that polynomial (Bayesian) regressions can be used for precise and accurate predictions of peaks and valleys in performance landscapes, irrespective of the underlying structure of the data (i.e., individual food intakes vs. fixed diet ratios). We then identified the known nutritional trade-off between life span and reproductive rate in terms of both nutrient balance and concentration for validation of the model. This showed that nutrigonometry enables a fast, reliable, and reproducible quantification of nutritional trade-offs in multidimensional performance landscapes, thereby broadening the potential for future developments in comparative research on the evolution of animal nutrition.

Nutrigonometry I: eesin richt-anngle trianngles tae compeer nutritional trade-affs in sindry lanscapes

Craiters sort oot foo muckle maet they ett tae mak e maist o the expression o fitness traits, bit maun niffer eemaist expression cause o odds in e nutrients nott in ilka trait (“nutritional trade-affs”). Nutritional trade-affs hiv been preeved wi experimints aat eese e Geometric Framework for Nutrition (GF). Fooivver, wyes tae mizzour sic trade-affs depen on aither eesin yer een or kittlie mathematical models pit tae sindry performance lanscapes, makin sic oncomes subjective, or ill tae unnerstan, dear tae wirk oot, an fyles jist plain wrang. Here, we pit forrit a haimalt trigonometric model tae mizzour nutritional trade-affs in sindry lanscapes (Nutrigonometry), att lippens one trigonometric sibness o richt-anngle trianngles, an sae, is aisier tae wirk oot, unnerstan an eese nor e wyes o wirkin it oot att wis eesed afore. We apply Nutrigonometry tae a lanmark GF set o data tae compeer a hantle o statistical models tae wirk oot foo weel e model’s deein in finnin regions i the performance lanscapes. Iss shewed att polynomial (Bayesian) regressions mith be eesed for preceese an exack weirds o heichest an laichest pints in performance lanscapes, regairdless o fit lies aneth e data (i.e., parteeclar intaks o maet or fixed diet ratios). Syne, we managed tae wirk oot e kent nutritional trade-aff atween foo lang life wad be an foo mony younng there wad be baith fae e pint o view o nutrient balance an concentration for validation o e model. Iss shews Nutrigonometry allooes a fest, siccar, an reproducible mizzour o nutritional trade-affs in sindry performance lanscapes, in att wye, raxin oot e possibeelity for groweth in comparative research on the evolution o craiters’ nutrition in days tae come.

Author Bio:

Dr. Dana Reuter is an NSF Postdoctoral Fellow working with the Florida Museum of Natural History and the Department of Ecology and Conservation Biology at Texas A&M. She studies the relationship among diet, biogeography, and morphology in mammals. She is also interested in community structure changes in deep time. Her additional interests include restoring vintage clothing, gardening, and exploring the outdoors.

“Seasonality and the Coexistence of Pathogen Strains”

Thu, 04 May 2023 05:00:00 GMT

Viggo Andreasen and Greg Dwyer, May 2023

Read the Article

Efforts by theoreticians to understand pathogen coexistence have focused on population structure, while unrealistically assuming constant conditions. Andreasen & Dwyer show that pathogen coexistence can arise because of seasonality, a mechanism that affects a broad range of systems

Have you ever been ill over the winter with a cold or the flu, started to recover, and then ended up catching a different “bug” before you were fully better? If you’ve ever thought about why so many more people become ill during the winter than do during the summer, you’ve noticed that seasonality can drive the transmission of disease.

The dynamics of seasonal pathogen coexistence are complex. To allow for coexistence, non-seasonal models must invoke spatial variation in host or pathogen densities or population structures. However, Dr. Viggo Andreasen of Roskilde University, Denmark and Dr. Greg Dwyer of the University of Chicago, USA, find that pathogen coexistence can instead be explained by temporal variation in host reproduction and pathogen transmission, and thus by seasonality.

In their study, Andreasen and Dwyer constructed a model in which pathogen fitness depends on both infectiousness during the epidemic period and survival in inter-epidemic periods. They then used their model to show how seasonality in host reproduction can foster strain coexistence. Seasonal epidemic periods are driven by an influx of susceptible new hosts due to reproduction, which provide an increased opportunity for infection. Coexistence is possible because strain fitness can be higher in either the epidemic period (just after the host reproduces) or the inter-epidemic period, permitting strains to pursue different infection strategies.

In the first pair of strategies that enable coexistence, one pathogen has very high inter-epidemic survival while the other pathogen has low inter-epidemic survival but infects more hosts and thus has a higher reproductive number. The strain with a higher reproductive number will be pushed toward extinction during inter-epidemic periods, but it can rebound during the epidemic period. A second pair of strategies that enable coexistence involve differences in initial epidemic fitness and reproductive rate. In this case, the strain with a lower reproductive number infects more hosts per unit time, and so it has a higher initial fitness that counterbalances its lower reproductive number. Seasonality can allow high-infectiousness/low-survival pathogen strains to coexist with low-infectiousness/high-survival pathogen strains in these two different ways.

Andreasen and Dwyer’s work thus highlights the importance of seasonal variation in driving pathogen coexistence. Further, their work shows that population structure is not a necessary precondition for pathogen coexistence. It turns out timing is everything, even for pathogens.

Abstract

Host-pathogen models usually explain the coexistence of pathogen strains by invoking population structure, meaning host or pathogen variation across space or individuals; most models, however, neglect the seasonal variation typical of host-pathogen interactions in nature. To determine the extent to which seasonality can drive pathogen coexistence, we constructed a model in which seasonal host reproduction fuels annual epidemics, which are in turn followed by interepidemic periods with no transmission, a pattern seen in many host-pathogen interactions in nature. In our model, a pathogen strain with low infectiousness and high interepidemic survival can coexist with a strain with high infectiousness and low interepidemic survival: seasonality thus permits coexistence. This seemingly simple type of coexistence can be achieved through two very different pathogen strategies, but understanding these strategies requires novel mathematical analyses. Standard analyses show that coexistence can occur if the competing strains differ in terms of R₀, the number of new infections per infectious life span in a completely susceptible population. A novel mathematical method of analyzing transient dynamics, however, allows us to show that coexistence can also occur if one strain has a lower R₀ than its competitor but a higher initial fitness &lambda₀, the number of new infections per unit time in a completely susceptible population. This second strategy allows coexisting pathogens to have quite similar phenotypes, whereas coexistence that depends on differences in R₀ values requires that coexisting pathogens have very different phenotypes. Our novel analytic method suggests that transient dynamics are an overlooked force in host-pathogen interactions.

Author Bio:

Madeline Eppley is a PhD student at Northeastern University studying the relationship between spatial and temporal evolution in marine systems. They use eastern oyster genomics to investigate patterns of adaptation to environment and disease across space and time. When they’re not tackling cool science, they tackle people as a rugby player for Northeastern.

"Partitioning the Apparent Temperature Sensitivity into Within- and Across-Taxa Responses: Revisiting the Difference between Autotrophic and Heterotrophic Protists"

Sat, 29 Apr 2023 05:00:00 GMT

Bingzhang Chen (陈炳章), David J. S. Montagnes, Qing Wang (王庆), Hongbin Liu (刘红斌), and Susanne Menden-Deuer, April 2023

Read the Article

Understanding how warming temperatures affect different kinds of organisms helps scientists predict how impending climate change will impact biodiversity. Temperature influences virtually all physiological functions, including metabolism and respiration. However, temperature may impact these functions differently in groups of organisms that metabolize nutrients and respire differently. Autotrophs such as plants and algae produce their own food through light, water, and chemicals (usually carbon dioxide). In contrast, heterotrophs such as animals and fungi obtain energy by eating other organisms. Additionally, autotrophs and heterotrophs respire —a common measure of energy expenditure—differently. Briefly, autotrophs intake CO2 and release O2, whereas heterotrophs intake O2 and release CO2. Increased temperatures lead to increased respiratory rates and consequently increased metabolic rates in both autotrophs and heterotrophs. Hence, climate change is likely to affect how these organisms maintain energetic equilibrium. For years, conventional analysis showed that heterotrophs were more sensitive to changes in temperature than autotrophs. This suggests that the metabolism of heterotrophs should increase more rapidly than that of autotrophs as temperatures rise, which may lead to dramatic food web and ecosystem changes.

While the scientific literature has largely accepted the notion that autotrophs are less thermally sensitive than heterotrophs, certain confounding factors need to be considered and addressed, such as controlling for variation within taxonomic groups. This is precisely the impetus behind the work of Chen et al. (2023), who developed a mathematical framework that partitions within- and across-taxa thermal sensitivities in protists, a kingdom of life encompassing both autotrophic and heterotrophic members. Through this approach, the authors identified that 92% of differences in the thermal sensitivity of autotrophs and heterotrophs could be explained by within-taxa responses.

In addition, Chen et al. (2023) showed that the extent to which thermal sensitivities differ among species was similar between autotrophs and heterotrophs. This is relevant, as it lends support to the “hotter-is partially-better” hypothesis as a potential mechanism behind the pattern retrieved by the authors. This hypothesis posits that maximal growth rates should increase with temperature, but adaptation of biochemical reactions is still partially limited by thermodynamics. Thus, while hotter is better in general, there are limits to thermal adaptation that impact all species regardless of their metabolism. In this sense, autotrophs and heterotrophs have a similar capacity to adapt to changing thermal regimes.

Through their work, Chen et al. (2023) showed that the current appreciation of lower temperature sensitivity in autotrophs compared to heterotrophs arose due to reductionist approaches that failed to control for within- and among-species trends. Importantly, the partitioning methodology employed in this study is readily applicable to any linear regression analysis that involves grouping. Thus, while the current study provides a step towards a more complete understanding of thermal adaptation in the context of energetics, the framework of Chen et al. (2023) can be applied in contexts ranging from phylogenetic analyses to comparisons between ecosystems.

Abstract

Conventional analyses suggest that the metabolism of heterotrophs is thermally more sensitive than that of autotrophs, implying that warming leads to pronounced trophodynamic imbalances. However, these analyses inappropriately combine within- and across-taxa trends. Our new analysis separates these, revealing that 92% of the difference in the apparent thermal sensitivity between autotrophic and heterotrophic protists does indeed arise from within-taxa responses. Fitness differences among taxa adapted to different temperature regimes only partially compensate for the positive biochemical relationship between temperature and growth rate within taxa, supporting the hotter-is-partially-better hypothesis. Our work highlights the importance of separating within- and across-taxa responses when comparing temperature sensitivities between groups, which is relevant to how trophic imbalances and carbon fluxes respond to warming.

分离种内和种间的温度敏感性：重新审视自养和异养单细胞真核生物的差异

传统研究认为异养生物代谢速率相比自养生物而言对温度变化更加敏感，因此升温会增强自养和异养过程的不平衡。然而，之前研究未曾合理区分种内和种间对温度响应的差异。本研究提出一种新的方法分离种内和种间对温度的不同响应，发现自养和异养单细胞真核生物的表观温度敏感性（活化能）的差异主要（92%）来自于种内关系。不同种对温度的适应提高了它们的生长率；然而此生长率的提高只能部分抵消种内温度对生长率的影响。本研究揭示了在比较不同生物之间温度敏感性时区分种内和种间关系的重要性。

Author Bio:

Danilo Giacometti is a PhD student at Brock University, ON, Canada. He is an eco-physiologist who focuses on understanding how organisms respond to environmental change on temporal scales. He studies aspects that are vital to organismal functioning, such as thermoregulation and energetics. Vertebrate ectotherms are his main study system, with a special emphasis on amphibians and non-avian reptiles.

2023 ASN Student Research Award

Thu, 13 Apr 2023 05:00:00 GMT

The recipients of the 2023 Student Research Awards are (in no particular order):

Krish Sanghvi, University of Oxford, Effects of paternal age, sperm storage duration, and lifespan, on offspring
Rachel Prokopius, Florida International University, The influence of pathogen presence on amphibian mate choice and resource allocation
Megan Barkdull, Cornell University, The genetic & evolutionary basis of a key ecological innovation: the Cephalotes ant soldier
Hengxing Zou, Rice University, Time-dependent effects of plant-microbe interactions
Ratna Karatgi, University of Illinois at Urbana-Champaign, Critical developmental windows for the expression of phenotypic plasticity in fin coloration in bluefin killifish (Lucania goodei)
Lydia Wong, University of Ottawa, Determinants of upper-elevation range limits in cavity-nesting bees and wasps
Erik Iverson, The University of Texas at Austin, Climatic adaptation and the future of biodiversity through the lens of an avian elevational series
Valerie Martin, Utah State University, Microbial mediation of bumblebee foraging tactics via modified flower phenotype
Mia Waters, The University of British Columbia, Eco-evolutionary consequences of increasing community diversity for evolutionary rescue
Hannah Assour, University of Pittsburgh, Is polyploid plant establishment favored under stressful conditions?

The ASN Student Research Awards support research by student members that advances the goals of the society: the conceptual unification of ecology, evolution, or behavior. Each award consists of a $2,000 check to the candidate. An applicant must be a member of the ASN (membership is international), must hold a bachelor’s degree or equivalent, must have passed to candidacy in a PhD program or equivalent, and must be at least one year from completing the PhD.

Projects in all types of research (i.e., laboratory, field, theory) are encouraged. Proposals are judged on originality, strength, and significance of the questions being addressed, prospects for significant results, and the match between the proposed research and the ASN mission.

Results of the 2023 Election

Wed, 12 Apr 2023 05:00:00 GMT

The ASN has chosen two new officers. We congratulate the winners, whose election statements are presented below, as well as the distinguished runners-up, Carol Boggs and Rafael Rodríguez.

Election Statement:
I am excited by the possibility of continuing to serve the American Society of Naturalists (ASN), should the members elect me as ASN President. This society has a nearly 150-year history of facilitating intellectual mergers between many areas of the natural sciences, reflected in my own values as a researcher. My research concerns the role of ecological interactions in the evolution of intraspecific variation in phenotypes, with a current emphasis on host-parasite interactions driving the evolution of host diet, behavior, and immunity. We draw on methods from genomics, immunology, cell biology, theory, field ecology, gene editing, and more. From this integrative work I have become ever more convinced by the value of unifying biological research.

I received my BA from Williams College (Biology, with a minor in Environmental Studies), which incidentally was the home of the first Secretary of the ASN in the 1870s. I learned of this connection when I started a Naturalists club during my first year in college, only to discover there had been a Williams Naturalists organization during the 1800s, affiliated with the ASN. I taught high school math and biology in Tanzania for the US Peace Corps, then went to graduate school in Population Biology at UC Davis with Peter Wainwright. After a brief postdoc with Michael Turelli, I began a faculty position in Integrative Biology at the University of Texas at Austin, interrupted by a 6-year position as an Early Career Scientist at the Howard Hughes Medical Institute. While at UT Austin, I received the ASN Young Investigator Prize, the Dobzhansky Award from SSE, and the George Mercer Award from the Ecological Society of America, a Packard Fellowship, an HHMI Early Career Scientist fellowship, the Edith and Peter O’Donnell Prize in Science from the Texas Academy of Medicine Engineering Science and Technology. In 2018 I moved to the University of Connecticut to enjoy the cooler climate and New England forests.

Through my career I have served the community in a variety of roles. I was the Secretary of the ASN for three years (followed by three additional years on the council as ex-secretary). As secretary I took the lead on organizing the first ASN Asilomar meeting (held in 2014), which was such a success that ASN has continued to hold stand-alone meetings there every other year since, and I was involved in helping with organization for some of these later meetings. I was an Associate Editor for The American Naturalist from 2008–2017, then Editor-In-Chief for five years. During my time as EIC I expanded the diversity of our editorial board, and took steps to improve the reproducibility of the science we publish. I pursued some cases of scientific misconduct, and created a team of Data Editors to enforce and ensure quality control for our new policy of requiring both data and code archives. Outside of the context of ASN, I also am serving on the SSE Council, and have been active in starting a very proactive DEI committee in my department in Connecticut.

The ASN plays a unique role at the intersection between biological disciplines, particularly evolution and ecology and behavior. It is first and foremost an intellectual community where people from very different intellectual traditions can trade ideas. Former Editor of Am Nat Robert Bigelow wrote in 1898, “We desire that our pages afford a common meeting-ground where the morphologist, the physiologist, the zoologist, the botanist, the anthropologist, the palaeontologist, the geologist, and the mineralogist may meet to discuss the problems in which they have a common interest”. Although the specific disciplines have changed, the sentiment still holds, that this is a common meeting-ground. This function provides networking and career-building opportunities for early-career scientists, and the generation of new research questions and ideas. So, the fundamental feature of the society ought to be bringing together people from many intellectual and cultural backgrounds for scientific conversation. As president I would prioritize virtual and affordable in-person opportunities for intellectual engagement by diverse members of our intellectual community, including improving opportunities for access and engagement by an increasingly global membership as well as continuing ongoing efforts to support under-represented groups within North America and Europe. I would like to also work with diverse other societies focused on related fields (ecology, behavior, genetics, and even more molecular/cellular groups, etc.) to build more opportunities for collaboration, for instance by pairing our broad conferences with some focused workshops co-sponsored by multiple societies, to improve the diversity of intellectual backgrounds and life experiences that we use to answer fundamental questions of organismal biology.

Election Statement:
I am a population biologist working at the interface of ecology and evolution. Much of my research focuses on the evolutionary ecology of species’ geographic distributions. My lab conducts empirical tests of hypotheses about limits to adaptation at range edges, capacity for evolutionary rescue as environments change, and the interplay of adaptive and non-adaptive evolution during range expansion. We conduct field, greenhouse, and lab studies on plant systems using a variety of tools including demographic models, field and common garden experiments, mesocosms, quantitative genetics, and genomics.

I completed a BA in Biology at Washington University in St. Louis, then moved to University of Washington for doctoral studies. I completed my PhD at Michigan State University, then moved to the University of Arizona to conduct postdoctoral research. In 2012 I became a member of the faculty at UBC, where I am jointly appointed in the departments of Botany and Zoology and hold a Tier 1 Canada Research Chair in Evolutionary Ecology.

I have been engaged in service in support of scientific societies throughout my career, including as chair of the Plant Population Ecology section of the Ecological Society of America and elected council member to the Society for the Study of Evolution. I have also served as Associate Editor for several journals, including The American Naturalist, Evolution, and Ecology Letters. Within my institution, I lead my department’s committee on equity, diversity, and inclusion and have been involved in faculty- and university-level initiatives to foster institutional change in support of EDI.

I am a member of ASN and I served as an Associate Editor for The American Naturalist from 2018-2021. Since 2018 I have also served on a tri-society committee that is creating a Code of Ethics for ASN, the Society for the Study of Evolution, and Society of Systematic Biologists. I would be honored to serve the ASN in the Vice President’s role because the ASN’s mission to promote conceptual unification in the biological sciences has inspired my integrative approach ever since I was a graduate student. I am particularly excited to help the society implement its Code of Ethics because I am committed to fostering a scientific community that is welcoming, fair, and transparent.

I would organize a VP symposium around the topic of coping with an increasingly extreme and variable world. I would invite speakers who approach this topic from a wide variety of angles, including those who focus on organismal-level functional responses, population-level demographic buffering and evolutionary rescue, and landscape-level changes in species distributions and community structure.

“Grooming Time Predicts Survival: American Kestrels, Falco sparverius, on a Subtropical Island”

Fri, 07 Apr 2023 05:00:00 GMT

Sarah E. Bush and Dale H. Clayton, April 2023

Read the Article

Grooming is a behavior observed in animals to care for their body surfaces. In birds, grooming consists of cleaning and arranging feathers, distributing preen oil that waterproofs the feathers and helps in odor-based communication, and clawing to get rid of any parasites among the feathers. All these behaviors may affect a bird’s health, although we lack concrete evidence of these potential links.

Many birds invest around 5-15% of their time in grooming on average, which may lead to tradeoffs if birds are grooming at the expense of activities like foraging and reproduction. This led Dr. Sarah Bush and Dr. Dale Clayton from the University of Utah to wonder: is there a relation between bird grooming and survival? To address this question, they conducted a field observation study of kestrels. They selected kestrels for this question due to their abundance and ability to be tamed, which makes them suitable for ‘capture, mark, and observe’ studies. Over the course of two years, they monitored a population of non-migratory American kestrels on the island of San Salvador in the Bahamas. Kestrels were selected for this study due to their abundance and ability to be tamed, which makes them suitable for ‘capture, mark, and observe’ studies. They banded seventy-two birds, collected data on their grooming behavior and parasite abundance, and measured their survival.

The authors found that kestrels who groomed an intermediate amount had the highest survival. This could be explained by the fact that low grooming rates may result in poor plumage (feather) quality which could impact mating success and increase parasite infection rates, while high rates may indicate that the bird is experiencing stress. Surprisingly, birds that groomed more did not have lower parasite loads, and a bird’s parasite load did not affect their survival. This may imply that the dynamics of parasite load and grooming are not tightly linked, or that the parasites found on the birds of this island may not be highly detrimental to the health of the birds. Bush and Clayton’s work is the first study to demonstrate a relationship between grooming behavior and survival. However, we do not currently know whether grooming behavior is a cause or a consequence of changes in survival probability, and it would be interesting to identify the mechanism through which grooming impacts survival.

Abstract

Animals have evolved a variety of adaptations to care for their body surfaces, such as grooming behavior, which keeps the integument clean, parasite-free, and properly arranged. Despite extensive research on the grooming of mammals, birds, and arthropods, the survival value of grooming has never been directly measured in natural populations. We monitored grooming and survival in a population of marked American kestrels (Falco sparverius) on San Salvador Island, Bahamas. We found a strong association between time spent grooming and survival over a 2-year period. The quadratic relationship we show is consistent with stabilizing natural selection on grooming time. To our knowledge, this is the first evidence for a correlation between grooming time and survival in a natural population. Grooming time may predict the survival of many animal taxa, but additional studies are needed to determine the shape and strength of the relationship among birds, mammals, and arthropods.

Author Bio:

Shubha Govindarajan is a PhD student with Deepa Agashe at the National Centre for Biological Sciences, Bengaluru, Karnataka, India. She is working on questions related to adaptation and niche expansion using flour beetles. Her additional interests include classical dance, music and literature.

2023 American Naturalist Student Paper Award

Mon, 03 Apr 2023 05:00:00 GMT

The American Naturalist 2023 Student Paper Award is for work that was published in 2022 and that was performed primarily by the first author and primarily while she or he was an undergraduate or graduate student. The Editors of the journal, in consultation with Associate Editors, examine all student-authored papers in the journal to select an outstanding contribution that advances the journal’s goals of changing the way people think about organismal biology (including but not limited to ecology, evolution, and behavior) by providing new conceptual insights.

Winner:

Zettlemoyer, Meredith A. 2022. “Monitoring demography of resurrected populations of locally extinct and extant species to investigate drivers of species loss.” The American Naturalist 200: E36–E51.

In this paper, Meredith Zettlemoyer poses an important question: why do some species go extinct with anthropogenic habitat changes while their close relatives persist? In the Anthropocene, communities are faced with a multitude of new disturbances and rapidly changing conditions that can lead to decline in natural populations and even extinction. But how can we determine what causes the differential extinction of species when they are no longer present in the community? Zettlemoyer overcomes this obstacle by conducting an ambitious experiment that reintroduces locally extinct species into the ecosystem to compare their demographic response to closely related sister taxa that persisted. Using sophisticated population models, she found that survival rates of locally extinct taxa were much more negatively affected by nitrogen deposition (a common effect of anthropogenic land use), despite potential positive effect on nitrogen on growth rates of individual plants. These results not only help explain why certain species have been lost from the local system, but also demonstrate how we can reveal the demographic differences between species that are successful in resisting anthropogenic disturbances and those that fail. The Editors of The American Naturalist were impressed with the creative question, elegant experimental design, and sophisticated population model and demographic analyses. This is a very nice example of how we can integrate experimental ecology with theory to tackle critical concepts in global change ecology, with important practical implications for the many conservation and management challenges we face today.

Honorable mention:

Bisschop, Karen, Adriana Alzate, Dries Bonte, and Rampal S. Etienne. 2022. “The demographic consequences of adaptation: evidence from experimental evolution.” The American Naturalist 199: 729–742.

Honorable mention goes to Karen Bisschop for the paper “The demographic consequences of adaptation: Evidence from experimental evolution.” When species invade new habitats, we expect that they acquire higher fitness through changes in life history traits. But how do these evolutionary changes affect the population dynamics of species? In this study, Bisshop and colleagues fit models to the dynamics of spider mite populations in immigration experiments to explore this connection between evolutionary and ecological dynamics. They found that adaptation increases population growth rates, but carrying capacity could either decrease or increase over time depending on the ecological conditions. Their work elegantly tests a complicated concept and provides clear evidence for the importance of evolution in driving population dynamics in changing environments.

“How Female-Female Competition Affects Male-Male Competition: Insights into Postcopulatory Sexual Selection from Socially Polyandrous Species”

Thu, 30 Mar 2023 05:00:00 GMT

Read the Article

In his 1871 book The Descent of Man, Charles Darwin proposed the then-revolutionary theory of sexual selection, which explained extravagant traits that seemed disadvantageous if we considered only his earlier theory of natural selection. As Darwin saw it, females tend to be choosy when selecting sexual mates, whereas males tend to be less discriminating. This leads to intense male-male competition for females, which in turn selects for elaborate ornamental traits in males such as loud songs, bright colors, and energetic dances. But two major wrinkles in the mechanics of sexual selection escaped Darwin. First, sexual selection persists even after copulation: inside the female reproductive tract, sperm compete for access to the egg and females of many species can regulate that access, which may lead to selection for sperm traits such as speed and size. Additionally, sexual selection is not a one way street: not only do males compete for females, but also vice-versa. In fact, female competition can be stronger than male competition in some species, reaching a zenith in socially polyandrous species, where females mate with multiple males, have more developed secondary sexual traits, and forgo most or even all parental care, leaving it for the males instead. One example of this is the Northern Jacana, a wading bird from Central America and the Caribbean. Female Northern Jacanas can be up to twice as heavy as males, reversing the more typical pattern of difference in body mass between the sexes in birds.

Sara Lipshutz and collaborators used the Northern Jacana to look into the intersection of those two wrinkles missed by Darwin. They reasoned that because female jacanas may copulate with up to three different males within a span of 20 minutes, this might set the stage for very strong sperm competition. They compared the Northern Jacana to a closely related species, the Wattled Jacana, which has a lower degree of social polyandry, expecting male Northern Jacanas to have larger sperm and testes than male Wattled Jacanas. Braving the logistical challenges of the jacanas’ tropical and swampy habitats in Panama, Lipshutz and colleagues were able to collect testes and ejaculates from 18 male jacanas from the two species, preserve them, and bring them back to the lab for detailed study. Their findings support the main prediction: the two components of sperm most associated with swimming ability, the tail and the midpiece, are longer in Northern than in Wattled Jacanas.

Their work corroborates the hypothesis that intense competition between females for males leads to intense sperm competition and changes in sperm morphology. Thus, the behavior of one sex may cause changes in the physiology and morphology of the other sex. This study is particularly important because most of our knowledge of sperm competition in birds derives from species with “traditional” sex roles, such as the Zebra Finch and the Red-Winged Blackbird. Charles Darwin wore the blinders typical of his time and social position that prevented him from focusing on females and seeing sexual selection as a two-way process. Thankfully today, as science becomes more diverse and scientists become more aware of our own biases, our research emphases are expanding, allowing us to learn more about the diversity of evolutionary processes in their full glorious detail that we might have otherwise missed.

Abstract

Sexual selection is a major driver of trait variation, and the intensity of male competition for mating opportunities has been linked with sperm size across diverse taxa. Mating competition among females may also shape the evolution of sperm traits, but the effect of the interplay between female-female competition and male-male competition on sperm morphology is not well understood. We evaluated variation in sperm morphology in two species with socially polyandrous mating systems, in which females compete to mate with multiple males. Northern jacanas (Jacana spinosa) and wattled jacanas (J. jacana) vary in their degree of social polyandry and sexual dimorphism, suggesting species differences in the intensity of sexual selection. We compared mean and variance in sperm head, midpiece, and tail length between species and breeding stages because these measures have been associated with the intensity of sperm competition. We found that the species with greater polyandry, northern jacana, has sperm with longer midpieces and tails as well as marginally lower intraejaculate variation in tail length. Intraejaculate variation was also significantly lower in copulating males than in incubating males, suggesting flexibility in sperm production as males cycle between breeding stages. Our results indicate that stronger female-female competition for mating opportunities may also shape more intense male-male competition by selecting for longer and less variable sperm traits. These findings extend frameworks developed in socially monogamous species to reveal that sperm competition may be an important evolutionary force layered atop female-female competition for mates.

Cómo la competencia entre hembras afecta la competencia entre machos: perspectivas sobre la selección sexual poscopulatoria de especies socialmente poliándricas

La selección sexual es un promotor principal de la variación de caracteres y la intensidad de la competencia entre machos por acceder al apareamiento, ha sido relacionado con el tamaño del espermatozoide en distintos taxa. La competencia entre las hembras por una pareja también puede mediar en la evolución de los rasgos espermáticos, pero aún no se comprende bien el efecto de las interacciones competitivas de hembras-hembras y machos-machos en la morfología del esperma. Evaluamos la variación morfológica de los espermatozoides en dos sistemas de apareamiento socialmente poliándricos, en los que las hembras compiten por copular con distintos machos. La jacana norteña (Jacana spinosa) y la jacana carunculada (J. jacana) varían en sus niveles de poliandría y dimorfismo sexual, sugiriendo diferencias entre especies en la intensidad de la selección sexual. Comparamos las medias y varianzas en las longitudes de la cabeza, segmento intermedio y cola de los espermatozoides entre estas especies y sus etapas reproductivas, ya que estas medidas se han asociado con la intensidad competitiva de los espermatozoides. Hallamos que los espermatozoides de la especie con poliandría más intensa, la jacana norteña, poseen segmentos intermedios y colas más largos, así como una variación intra-eyacular marginalmente reducida en la longitud de la cola. La variación intra-eyacular también fue significativamente menor en machos copuladores con respecto a los incubadores, lo que sugiere una flexibilidad en la producción de esperma entre las etapas del ciclo reproductivo. Nuestros resultados indican que una competencia más intensa entre hembras por oportunidades de cópula también puede dar lugar a una competencia más intensa entre machos al seleccionar espermas con rasgos más largos y menos variables. Estos hallazgos amplían las nociones sobre la competencia espermática, desarrollados en especies socialmente monógamas, para revelar que la competencia espermática puede ser una fuerza evolutiva importante superpuesta a la competencia entre hembras por parejas.

Author Bio:

Dr. Rafael Marcondes is an ornithologist and evolutionary biologist. His research centers on using birds as models to answer fundamental questions in evolutionary biology, especially related to phenotypic diversification. He received his Ph.D. from Louisiana State University and is currently a faculty-fellow at Rice University.