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1. Population expansion, divergence, and persistence in Western Fence Lizards (Sceloporus occidentalis) at the northern extreme of their distributional range

   https://doi.org/10.1038/s41598-022-10233-9  

   Davis, Hayden R.; Des Roches, Simone; Anderson, Roger A.; Leaché, Adam D. (December 2022, Scientific Reports)

   Abstract Population dynamics within species at the edge of their distributional range, including the formation of genetic structure during range expansion, are difficult to study when they have had limited time to evolve. Western Fence Lizards ( Sceloporus occidentalis ) have a patchy distribution at the northern edge of their range around the Puget Sound, Washington, where they almost exclusively occur on imperiled coastal habitats. The entire region was covered by Pleistocene glaciation as recently as 16,000 years ago, suggesting that populations must have colonized these habitats relatively recently. We tested for population differentiation across this landscape using genome-wide SNPs and morphological data. A time-calibrated species tree supports the hypothesis of a post-glacial establishment and subsequent population expansion into the region. Despite a strong signal for fine-scale population genetic structure across the Puget Sound with as many as 8–10 distinct subpopulations supported by the SNP data, there is minimal evidence for morphological differentiation at this same spatiotemporal scale. Historical demographic analyses suggest that populations expanded and diverged across the region as the Cordilleran Ice Sheet receded. Population isolation, lack of dispersal corridors, and strict habitat requirements are the key drivers of population divergence in this system. These same factors may prove detrimental to the future persistence of populations as they cope with increasing shoreline development associated with urbanization. 

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2. Adaptive Divergence of Meiotic Recombination Rate in Ecological Speciation

   https://doi.org/10.1093/gbe/evaa182  

   Neupane, Swatantra; Xu, Sen (October 2020, Genome Biology and Evolution)

   Baer, Charles (Ed.)

   Abstract Theories predict that directional selection during adaptation to a novel habitat results in elevated meiotic recombination rate. Yet the lack of population-level recombination rate data leaves this hypothesis untested in natural populations. Here, we examine the population-level recombination rate variation in two incipient ecological species, the microcrustacean Daphnia pulex (an ephemeral-pond species) and Daphnia pulicaria (a permanent-lake species). The divergence of D. pulicaria from D. pulex involved habitat shifts from pond to lake habitats as well as strong local adaptation due to directional selection. Using a novel single-sperm genotyping approach, we estimated the male-specific recombination rate of two linkage groups in multiple populations of each species in common garden experiments and identified a significantly elevated recombination rate in D. pulicaria. Most importantly, population genetic analyses show that the divergence in recombination rate between these two species is most likely due to divergent selection in distinct ecological habitats rather than neutral evolution. 

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3. Dispersive currents explain patterns of population connectivity in an ecologically and economically important fish

   https://doi.org/10.1111/eva.13567  

   Schraidt, Claire E.; Ackiss, Amanda S.; Larson, Wesley A.; Rowe, Mark D.; Höök, Tomas O.; Christie, Mark R. (July 2023, Evolutionary Applications)

   Abstract How to identify the drivers of population connectivity remains a fundamental question in ecology and evolution. Answering this question can be challenging in aquatic environments where dynamic lake and ocean currents coupled with high levels of dispersal and gene flow can decrease the utility of modern population genetic tools. To address this challenge, we used RAD‐Seq to genotype 959 yellow perch (Perca flavescens), a species with an ~40‐day pelagic larval duration (PLD), collected from 20 sites circumscribing Lake Michigan. We also developed a novel, integrative approach that couples detailed biophysical models with eco‐genetic agent‐based models to generate “predictive” values of genetic differentiation. By comparing predictive and empirical values of genetic differentiation, we estimated the relative contributions for known drivers of population connectivity (e.g., currents, behavior, PLD). For the main basin populations (i.e., the largest contiguous portion of the lake), we found that high gene flow led to low overall levels of genetic differentiation among populations (F_ST = 0.003). By far the best predictors of genetic differentiation were connectivity matrices that were derived from periods of time when there were strong and highly dispersive currents. Thus, these highly dispersive currents are driving the patterns of population connectivity in the main basin. We also found that populations from the northern and southern main basin are slightly divergent from one another, while those from Green Bay and the main basin are highly divergent (F_ST = 0.11). By integrating biophysical and eco‐genetic models with genome‐wide data, we illustrate that the drivers of population connectivity can be identified in high gene flow systems. 

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4. Elevated Temperature Reduces Overwintering Survival of an Avian Ectoparasite, the Swallow Bug (Hemiptera: Cimicidae: Cimex vicarius )

   https://doi.org/10.1093/ee/nvac015  

   Brown, Charles R; Hannebaum, Stacey L; Eaton-Clark, Andrew; Booth, Warren; O’Brien, Valerie A (March 2022, Environmental Entomology)

   Mercader, Rodrigo (Ed.)

   Abstract The survival of insects that are dormant in winter may either increase or decrease as a consequence of elevated winter temperatures under climate change. Warming can be deleterious when metabolism of the overwintering life stages increases to the point that energy reserves are exhausted before postoverwintering reemergence. We examined experimentally how overwintering survival of swallow bugs (Hemiptera: Cimicidae: Cimex vicarius Horvath), an ectoparasite primarily of cliff swallows (Passeriformes: Hirundinidae: Petrochelidon pyrrhonota Vieillot), was affected by a 3°C rise in mean daily temperature for populations in Oklahoma, Nebraska, and North Dakota. Adult and nymphal swallow bugs exposed to elevated temperature had an average reduction of approximately 31% in overwintering survival (from July/August to April/May), relative to controls exposed to current region-specific ambient-like conditions. Adult males in both groups survived less well in Nebraska and North Dakota than adult males in Oklahoma, but there was no consistent latitudinal effect of the elevated heat treatment. Our results indicate that projected increases in mean temperature in the Great Plains by 2050 could result in fewer swallow bugs surviving the winter and thus a reduced population size upon the arrival of their primary host in the spring, potentially affecting cliff swallow reproductive success, site use, and breeding phenology. Global climate change may alter the dynamics of host–parasite systems by reducing overall parasite abundance. 

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5. Fine-Scale Population Structure but Limited Genetic Differentiation in a Cooperatively Breeding Paper Wasp

   https://doi.org/10.1093/gbe/evaa070  

   Bluher, Sarah E; Miller, Sara E; Sheehan, Michael J; Baer, Charles (May 2020, Genome Biology and Evolution)

   Abstract Relatively little is known about the processes shaping population structure in cooperatively breeding insect species, despite the long-hypothesized importance of population structure in shaping patterns of cooperative breeding. Polistes paper wasps are primitively eusocial insects, with a cooperative breeding system in which females often found nests in cooperative associations. Prior mark-recapture studies of Polistes have documented extreme female philopatry, although genetic studies frequently fail to detect the strong population structure expected for highly philopatric species. Together these findings have led to lack of consensus on the degree of dispersal and population structure in these species. This study assessed population structure of female Polistes fuscatus wasps at three scales: within a single site, throughout Central New York, and across the Northeastern United States. Patterns of spatial genetic clustering and isolation by distance were observed in nuclear and mitochondrial genomes at the continental scale. Remarkably, population structure was evident even at fine spatial scales within a single collection site. However, P. fuscatus had low levels of genetic differentiation across long distances. These results suggest that P. fuscatus wasps may employ multiple dispersal strategies, including extreme natal philopatry as well as longer-distance dispersal. We observed greater genetic differentiation in mitochondrial genes than in the nuclear genome, indicative of increased dispersal distances in males. Our findings support the hypothesis that limited female dispersal contributes toward population structure in paper wasps. 

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