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1. Recent warming reduces the reproductive advantage of large size and contributes to evolutionary downsizing in nature

   https://doi.org/10.1098/rspb.2020.0608  

   Fryxell, David C.; Hoover, Alexander N.; Alvarez, Daniel A.; Arnesen, Finn J.; Benavente, Javiera N.; Moffett, Emma R.; Kinnison, Michael T.; Simon, Kevin S.; Palkovacs, Eric P. (June 2020, Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   Body size is a key functional trait that is predicted to decline under warming. Warming is known to cause size declines via phenotypic plasticity, but evolutionary responses of body size to warming are poorly understood. To test for warming-induced evolutionary responses of body size and growth rates, we used populations of mosquitofish ( Gambusia affinis ) recently established (less than 100 years) from a common source across a strong thermal gradient (19–33°C) created by geothermal springs. Each spring is remarkably stable in temperature and is virtually closed to gene flow from other thermal environments. Field surveys show that with increasing site temperature, body size distributions become smaller and the reproductive advantage of larger body size decreases. After common rearing to reveal recently evolved trait differences, warmer-source populations expressed slowed juvenile growth rates and increased reproductive effort at small sizes. These results are consistent with an adaptive basis of the plastic temperature–size rule, and they suggest that temperature itself can drive the evolution of countergradient variation in growth rates. The rapid evolution of reduced juvenile growth rates and greater reproduction at a small size should contribute to substantial body downsizing in populations, with implications for population dynamics and for ecosystems in a warming world. 

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2. Impacts of heavy metal pollution on the ionomes and transcriptomes of Western mosquitofish ( Gambusia affinis )

   https://doi.org/10.1111/mec.16342  

   Coffin, John L.; Kelley, Joanna L.; Jeyasingh, Punidan D.; Tobler, Michael (January 2022, Molecular Ecology)

   Abstract Our understanding of the mechanisms mediating the resilience of organisms to environmental change remains lacking. Heavy metals negatively affect processes at all biological scales, yet organisms inhabiting contaminated environments must maintain homeostasis to survive. Tar Creek in Oklahoma, USA, contains high concentrations of heavy metals and an abundance of Western mosquitofish (Gambusia affinis), though several fish species persist at lower frequency. To test hypotheses about the mechanisms mediating the persistence and abundance of mosquitofish in Tar Creek, we integrated ionomic data from seven resident fish species and transcriptomic data from mosquitofish. We predicted that mosquitofish minimize uptake of heavy metals more than other Tar Creek fish inhabitants and induce transcriptional responses to detoxify metals that enter the body, allowing them to persist in Tar Creek at higher density than species that may lack these responses. Tar Creek populations of all seven fish species accumulated heavy metals, suggesting mosquitofish cannot block uptake more efficiently than other species. We found population‐level gene expression changes between mosquitofish in Tar Creek and nearby unpolluted sites. Gene expression differences primarily occurred in the gill, where we found upregulation of genes involved with lowering transfer of metal ions from the blood into cells and mitigating free radicals. However, many differentially expressed genes were not in known metal response pathways, suggesting multifarious selective regimes and/or previously undocumented pathways could impact tolerance in mosquitofish. Our systems‐level study identified well characterized and putatively new mechanisms that enable mosquitofish to inhabit heavy metal‐contaminated environments. 

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3. Nonparallel transcriptional divergence during parallel adaptation

   https://doi.org/10.1111/mec.15823  

   Fischer, Eva K.; Song, Youngseok; Hughes, Kimberly A.; Zhou, Wen; Hoke, Kim L. (March 2021, Molecular Ecology)

   Abstract How underlying mechanisms bias evolution toward predictable outcomes remains an area of active debate. In this study, we leveraged phenotypic plasticity and parallel adaptation across independent lineages of Trinidadian guppies (Poecilia reticulata) to assess the predictability of gene expression evolution during parallel adaptation. Trinidadian guppies have repeatedly and independently adapted to high‐ and low‐predation environments in the wild. We combined this natural experiment with a laboratory breeding design to attribute transcriptional variation to the genetic influences of population of origin and developmental plasticity in response to rearing with or without predators. We observed substantial gene expression plasticity, as well as the evolution of expression plasticity itself, across populations. Genes exhibiting expression plasticity within populations were more likely to also differ in expression between populations, with the direction of population differences more likely to be opposite those of plasticity. While we found more overlap than expected by chance in genes differentially expressed between high‐ and low‐predation populations from distinct evolutionary lineages, the majority of differentially expressed genes were not shared between lineages. Our data suggest alternative transcriptional configurations associated with shared phenotypes, highlighting a role for transcriptional flexibility in the parallel phenotypic evolution of a species known for rapid adaptation. 

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4. A century of intermittent eco‐evolutionary feedbacks resulted in novel trait combinations in invasive Great Lakes alewives ( Alosa pseudoharengus )

   https://doi.org/10.1111/eva.13063  

   Smith, Shelby E.; Palkovacs, Eric P.; Weidel, Brian C.; Bunnell, David B.; Jones, Andrew W.; Bloom, Devin D. (August 2020, Evolutionary Applications)

   Abstract Species introductions provide opportunities to quantify rates and patterns of evolutionary change in response to novel environments. Alewives (Alosa pseudoharengus) are native to the East Coast of North America where they ascend coastal rivers to spawn in lakes and then return to the ocean. Some populations have become landlocked within the last 350 years and diverged phenotypically from their ancestral marine population. More recently, alewives were introduced to the Laurentian Great Lakes (~150 years ago), but these populations have not been compared to East Coast anadromous and landlocked populations. We quantified 95 years of evolution in foraging traits and overall body shape of Great Lakes alewives and compared patterns of phenotypic evolution of Great Lakes alewives to East Coast anadromous and landlocked populations. Our results suggest that gill raker spacing in Great Lakes alewives has evolved in a dynamic pattern that is consistent with responses to strong but intermittent eco‐evolutionary feedbacks with zooplankton size. Following their initial colonization of Lakes Ontario and Michigan, dense alewife populations likely depleted large‐bodied zooplankton, which drove a decrease in alewife gill raker spacing. However, the introduction of large, non‐native zooplankton to the Great Lakes in later decades resulted in an increase in gill raker spacing, and present‐day Great Lakes alewives have gill raker spacing patterns that are similar to the ancestral East Coast anadromous population. Conversely, contemporary Great Lakes alewife populations possess a gape width consistent with East Coast landlocked populations. Body shape showed remarkable parallel evolution with East Coast landlocked populations, likely due to a shared response to the loss of long‐distance movement or migrations. Our results suggest the colonization of a new environment and cessation of migration can result in rapid parallel evolution in some traits, but contingency also plays a role, and a dynamic ecosystem can also yield novel trait combinations. 

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5. Strong bat predation and weak environmental constraints predict longer moth tails

   https://doi.org/10.1098/rspb.2024.2824  

   Rubin, Juliette J; Campbell, Caitlin J; Carvalho, Ana_Paula S; St_Laurent, Ryan A; Crespo, Gina I; Pierson, Taylor L; Guralnick, Robert; Kawahara, Akito Y (May 2025, Proceedings of the Royal Society B: Biological Sciences)

   Elaborate traits evolve via intense selective pressure, overpowering ecological constraints. Hindwing tails that thwart bat attack have repeatedly originated in moon moths (Saturniidae), with longer tails having greater anti-predator effect. Here, we take a macroevolutionary approach to evaluate the evolutionary balance between predation pressure and possible limiting environmental factors on tail elongation. To trace the evolution of tail length across time and space, we inferred a time-calibrated phylogeny of the entirely tailed moth group (Actias + Argema) and performed ancestral state reconstruction and biogeographical analyses. We generated metrics of predation via estimates of bat abundance from nearly 200 custom-built species distribution models and environmental metrics via estimates of bioclimatic variables associated with individual moth observations. To access community science data, we developed a novel method for measuring wing lengths from un-scaled photos. Integrating these data into phylogenetically informed mixed models, we find a positive association between bat predation pressure and moth tail length and body size, and a negative association between environmental factors and these morphological traits. Regions with more insectivorous bats and more consistent temperatures tend to host longer-tailed moths. Our study provides insight into tradeoffs between biotic selective pressures and abiotic constraints that shape elaborate traits across the tree of life. 

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