Nunziata: Microevolutionary response of two salamander species to climate change in an isolated seasonal wetland

Climate change can strongly affect natural populations. Through its influence, many species will experience changes in their population demographics, shifts in the seasonal timing of life history characteristics (phenology), and possibly even extinction (Franks et al. 2007; Todd et al. 2010; Lane et al. 2011; Bálint et al. 2011). Global temperatures are projected to increase by several degrees (+1.8 to +4.0C) over the next century and models are needed to predict how species will respond (Meehl et al. 2007); however, little empirical information exists concerning the phenology, demographics, and genetics of species to inform the development of these models. Current changes in species’ phenology could serve as an indication of what species are responding to climate change, and what species might persist or decline in response (Cleland et al. 2012). While changes in phenology of individuals allow short-term population persistence, it is unclear what impact this will have on genetic variation, which is the basis for adaptation and long-term survival (Lande & Shannon 1996). The study of responses to environmental change is especially important in species with limited dispersal abilities, such as amphibians, as range shifts may be limited. Findings from a 30-year study monitoring the amphibian community at Rainbow Bay (RB), an ephemeral wetland in eastern South Carolina, found increasing temperature to be positively correlated with shifts in the timing of breeding migrations in some species, negatively correlated in other species, and uncorrelated with phenology in other species (Todd et al. 2010). As a potential compounding effect, increased droughts at RB from 1978-2004 have resulted in decreased hydroperiods and have been shown to be significantly correlated with population declines in amphibian species adapted to long hydroperiods (Daszak et al. 2005). The resolution of phenological responses and population declines related to climate-associated factors is important, but the equally important question of how these changes have impacted demography and the loss or maintenance of genetic variation remains unclear (Franks et al. 2007; Lane et al. 2011). Collectively, these climate-associated factors have impacted the population dynamics of the amphibian community at RB by causing a community dominance shift among species. For example, the salamander Ambystoma opacum has advanced its breeding time by 15.3 days, and the population has steadily expanded in numbers since colonizing RB in 1980. In contrast, A. talpoideum has not shifted its breeding time and its population has steadily declined since 1980. The response to climate change of these two species over time can address many questions related to the ecological genomics of climate change adaptation. Here, we propose research objectives aimed at understanding how phenological and demographic responses to climate change impacts the population genetics and evolution of amphibian species. Rainbow Bay provides a unique opportunity for this work because amphibian species have been continuously sampled over the last 30 years, providing a valuable time series across a period of years in which climatological and ecological conditions have changed significantly. Using restriction-site-associated DNA (RAD) sequencing, we will (1) generate genomic surveys of single nucleotide polymorphisms (SNPs) from a salamander species (A. opacum) that has demonstrated a population expansion at RB and a salamander species (A. talpoideum) that has declined in numbers. For each species, genomic data will be collected from three different time points, representing early, intermediate, and late stages across the last 30 years of climatological and ecological change at RB. We will use these data to then (2) assess intraspecific trends in population genetic parameters over time and compare interspecific trends. Finally, we will (3) use the time series of SNP variation within each species to identify loci that may be potentially influenced by selection as a result of climate change. These results will not only be informative at a local scale, but will be useful in beginning to model the genetic responses of amphibian populations at a regional-scale.