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1. Genome‐wide diversity and habitat underlie fine‐scale phenotypic differentiation in the rainbow darter ( Etheostoma caeruleum )

   https://doi.org/10.1111/eva.13135  

   Oliveira, Daniel R. ; Reid, Brendan N. ; Fitzpatrick, Sarah W. ( October 2020 , Evolutionary Applications)

   Adaptation to environmental change requires that populations harbor the necessary genetic variation to respond to selection. However, dispersal‐limited species with fragmented populations and reduced genetic diversity may lack this variation and are at an increased risk of local extinction. In freshwater fish species, environmental change in the form of increased stream temperatures places many cold‐water species at‐risk. We present a study of rainbow darters (Etheostoma caeruleum) in which we evaluated the importance of genetic variation on adaptive potential and determined responses to extreme thermal stress. We compared fine‐scale patterns of morphological and thermal tolerance differentiation across eight sites, including a unique lake habitat. We also inferred contemporary population structure using genomic data and characterized the relationship between individual genetic diversity and stress tolerance. We found site‐specific variation in thermal tolerance that generally matched local conditions and morphological differences associated with lake‐stream divergence. We detected patterns of population structure on a highly local spatial scale that could not be explained by isolation by distance or stream connectivity. Finally, we showed that individual thermal tolerance was positively correlated with genetic variation, suggesting that sites with increased genetic diversity may be better at tolerating novel stress. Our results highlight the importance of considering intraspecific variation in understanding population vulnerability and stress response.

    

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2. Landscape genomic signatures indicate reduced gene flow and forest‐associated adaptive divergence in an endangered neotropical turtle

   https://doi.org/10.1111/mec.15112  

   Gallego‐García, Natalia ; Forero‐Medina, Germán ; Vargas‐Ramírez, Mario ; Caballero, Susana ; Shaffer, Howard Bradley ( June 2019 , Molecular Ecology)

   Human‐induced transformations of ecosystems usually result in fragmented populations subject to increased extinction risk. Fragmentation is also often associated with novel environmental heterogeneity, which in combination with restricted gene flow may increase the opportunity for local adaptation. To manage at‐risk populations in these landscapes, it is important to understand how gene flow is changing, and how populations respond to habitat loss. We conducted a landscape genomics analysis using Restriction‐site Associated DNA sequencing to investigate the evolutionary response of the critically endangered Dahl's Toad‐headed turtle (Mesoclemmys dahli) to severe habitat modification. The species has lost almost all of its natural habitat in the southwestern part of its range and about 70% in the northeast. Based on least cost path analysis across different resistance surfaces for 3,211 SNPs, we found that the landscape matrix is restricting gene flow, causing the fragmentation of the species into at least six populations. Genome scans and allele‐environment association analyses indicate that the population fragments in the deforested grasslands of the southwest are adaptively different from those in the more forested northeast. Populations in areas with no forest had low levels of adaptive genetic diversity and the fixation of ancestrally‐polymorphic SNPs, consistent with directional selection in this novel environment. Our results suggest that this forest‐stream specialist is adapting to pond‐grassland conditions, but it is also suffering from negative consequences of habitat loss, including genetic erosion, isolation, small effective population sizes, and inbreeding. We recommend gene flow restoration via genetic rescue to counteract these threats, and provide guidance for this strategy.

    

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3. Macroecological predictors of evolutionary and plastic potential do not apply at microgeographic scales for a freshwater cladoceran under climate change

   https://doi.org/10.1093/evlett/qrad042  

   Nadeau, Christopher P. ; Urban, Mark C. ( October 2023 , Evolution Letters)

   Rapid evolutionary adaptation could reduce the negative impacts of climate change if sufficient heritability of key traits exists under future climate conditions. Plastic responses to climate change could also reduce negative impacts. Understanding which populations are likely to respond via evolution or plasticity could therefore improve estimates of extinction risk. A large body of research suggests that the evolutionary and plastic potential of a population can be predicted by the degree of spatial and temporal climatic variation it experiences. However, we know little about the scale at which these relationships apply. Here, we test if spatial and temporal variation in temperature affects genetic variation and plasticity of fitness and a key thermal tolerance trait (critical thermal maximum; CTmax) at microgeographic scales using a metapopulation of Daphnia magna in freshwater rock pools. Specifically, we ask if (a) there is a microgeographic adaptation of CTmax and fitness to differences in temperature among the pools, (b) pools with greater temporal temperature variation have more genetic variation or plasticity in CTmax or fitness, and (c) increases in temperature affect the heritability of CTmax and fitness. Although we observed genetic variation and plasticity in CTmax and fitness, and differences in fitness among pools, we did not find support for the predicted relationships between temperature variation and genetic variation or plasticity. Furthermore, the genetic variation and plasticity we observed in CTmax are unlikely sufficient to reduce the impacts of climate change. CTmax plasticity was minimal and heritability was 72% lower when D. magna developed at the higher temperatures predicted under climate change. In contrast, the heritability of fitness increased by 53% under warmer temperatures, suggesting an increase in overall evolutionary potential unrelated to CTmax under climate change. More research is needed to understand the evolutionary and plastic potential under climate change and how that potential will be altered in future climates.

    

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4. Negative relationship between thermal tolerance and plasticity in tolerance emerges during experimental evolution in a widespread marine invertebrate

   https://doi.org/10.1111/eva.13270  

   Sasaki, Matthew C. ; Dam, Hans G. ( July 2021 , Evolutionary Applications)

   Whether populations can adapt to predicted climate change conditions, and how rapidly, are critical questions for the management of natural systems. Experimental evolution has become an important tool to answer these questions. In order to provide useful, realistic insights into the adaptive response of populations to climate change, there needs to be careful consideration of how genetic differentiation and phenotypic plasticity interact to generate observed phenotypic changes. We exposed three populations of the widespread copepodAcartia tonsa(Crustacea) to chronic, sublethal temperature selection for 15 generations. We generated thermal survivorship curves at regular intervals both during and after this period of selection to track the evolution of thermal tolerance. Using reciprocal transplants between ambient and warming conditions, we also tracked changes in the strength of phenotypic plasticity in thermal tolerance. We observed significant increases in thermal tolerance in the Warming lineages, while plasticity in thermal tolerance was strongly reduced. We suggest these changes are driven by a negative relationship between thermal tolerance and plasticity in thermal tolerance. Our results indicate that adaptation to warming through an increase in thermal tolerance might not reduce vulnerability to climate change if the increase comes at the expense of tolerance plasticity. These results illustrate the importance of considering changes in both a trait of interest and the trait plasticity during experimental evolution.

    

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5. Spatial and temporal variation in phenotypes and fitness in response to developmental thermal environments

   https://doi.org/10.1111/1365-2435.13910  

   Pruett, Jenna E. ; Warner, Daniel A. ( October 2021 , Functional Ecology)

   Phenotypic variation within populations is influenced by the environment via plasticity and natural selection. How phenotypes respond to the environment can vary among traits, populations and life stages in ways that can influence fitness.

   Plastic responses during early development are particularly important because they can affect components of fitness throughout an individual's life. Consequently, how natural selection shapes developmental plasticity could be influenced by fitness consequences across different life stages. Moreover, spatial variation in selection pressures could generate differences in plastic responses among populations.

   To gain insight into sources of variation in phenotypes and survival, we used a laboratory egg incubation experiment using brown anole lizardsAnolis sagreifrom mainland (ancestral) and island (descendent) populations, combined with a mark–release–recapture experiment in the field. Our study was designed to (a) quantify the effects developmental temperature on embryo development and offspring morphology, (b) assess how developmental temperature influences offspring survival across different life stages and (c) quantify how thermal reaction norms vary among ancestral and descendant populations.

   Developmental temperature influenced offspring morphology, but thermal reaction norms of embryos showed little variation among populations. Developmental temperature influenced offspring survival, but the patterns differed between embryo and hatchling stages; the optimal temperature for embryos was about 5℃ lower than that for hatchlings. High temperatures were thermally stressful to embryos, but they reduced incubation duration and led to early hatching. In turn, earlier hatching increased the probability of survival to adulthood. Moreover, the effect of developmental temperature on hatchling survival was most pronounced for offspring that hatched late in the season.

   The difference in optimal developmental temperatures between life stages may be driven by physiological tolerance for embryos and by ecological factors for hatchlings. Moreover, the fitness consequences of the developmental environment depend on the phenology of hatching. Overall, these results highlight how the developmental environment can differentially affect fitness across life stages and show that temporal thermal heterogeneity can influence survival of embryos, but the consequences on post‐hatching stages may vary at different times of the season.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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