Demographic history and genomic signatures of selection in a widespread vertebrate ectotherm.

Environmental conditions vary greatly across large geographic ranges, and yet certain species inhabit entire continents. In such species, genomic sequencing can inform our understanding of colonization history and the impact of selection on the genome as populations experience diverse local environments. As ectothermic vertebrates are among the most vulnerable to environmental change, it is critical to understand the contributions of local adaptation to population survival. Widespread ectotherms offer an opportunity to explore how species can successfully inhabit such differing environments and how future climatic shifts will impact species' survival. In this study, we investigated the widespread painted turtle (Chrysemys picta) to assess population genomic structure, demographic history, and genomic signatures of selection in the western extent of the range. We found support for a substantial role of serial founder effects in shaping population genomic structure: demographic analysis and runs of homozygosity were consistent with bottlenecks of increasing severity from eastern to western populations during and following the Last Glacial Maximum, and edge populations were more strongly diverged and had less genetic diversity than those from the centre of the range. We also detected outlier loci, but allelic patterns in many loci could be explained by either genetic surfing or selection. While range expansion complicates the identification of loci under selection, we provide candidates for future study of local adaptation in a long-lived, widespread ectotherm that faces an uncertain future as the global climate continues to rapidly change.

Genetic rescue remains underused for aiding recovery of federally listed vertebrates in the United States.

Restoring gene flow among fragmented populations is discussed as a potentially powerful management strategy that could reduce inbreeding depression and cause genetic rescue. Yet, examples of assisted migration for genetic rescue remain sparse in conservation, prompting several outspoken calls for its increased use in genetic management of fragmented populations. We set out to evaluate the extent to which this strategy is underused and to determine how many imperiled species would realistically stand to benefit from genetic rescue, focusing on federally threatened or endangered vertebrate species in the United States. We developed a "genetic rescue suitability index (GR index)" based on concerns about small population problems relative to risks associated with outbreeding depression and surveyed the literature for 222 species. We found that two-thirds of these species were good candidates for consideration of assisted migration for the purpose of genetic rescue according to our suitability index. Good candidate species spanned all taxonomic groups and geographic regions, though species with more missing data tended to score lower on the suitability index. While we do not recommend a prescriptive interpretation of our GR index, we used it here to establish that assisted migration for genetic rescue is an underused strategy. For example, we found in total, "genetic rescue" was only mentioned in 11 recovery plans and has only been implemented in 3 of the species we surveyed. A potential way forward for implementation of this strategy is incorporating genetic rescue as a priority in USFWS recovery documentation. In general, our results suggest that although not appropriate for all imperiled species, many more species stand to benefit from a conservation strategy of assisted migration for genetic rescue than those for which it has previously been considered or implemented.

Immunosenescence and its influence on reproduction in a long-lived vertebrate.

Immunosenescence is a well-known phenomenon in mammal systems, but its relevance in other long-lived vertebrates is less understood. Further, the influence of age and reproductive effort on immune function in long-lived species can be challenging to assess, as long-term data are scarce and it is often difficult to sample the oldest age classes. We used the painted turtle (Chrysemys picta) to test hypotheses of immunosenescence and a trade-off between reproductive output and immune function in a population of a long-lived vertebrate that has been monitored for over 30 years. These long-term data were utilized to employ a unique approach of aging turtles with mark-recapture data and population-specific growth modeling to obtain more accurate estimates of age. We analyzed natural antibodies, lysis ability and bactericidal competence in 126 individuals from 1 to 33 years of age captured during May and June 2011. Older turtles exhibited greater natural antibody levels than young individuals. Young females with large clutches exhibited greater lysis ability, while older females with large clutches had decreased lysis ability, suggesting a trade-off between reproductive output and immune function conditional upon age. However, bactericidal competence increased later in the nesting season for older females. Our study rejects the hypothesis of immunosenescence in a long-lived turtle, despite evidence of actuarial and reproductive senescence in this population. Additionally, we detected mixed evidence for a trade-off between reproduction and immune health.