The Past as a Window to the Future: Phylogeography, Historical Demography, and Conservation Genetics of Plethodon jordani, a Terrestrial Salamander Endemic to the Great Smoky Mountains

Abstract

My dissertation research explores historic and climatic factors underlying geographic patterns of genetic structure in Plethodon jordani, a salamander that is endemic to the Great Smoky Mountains of eastern North America. Chapter 1 is collaborative work with Ben Weinstein, Dr. Matt Gifford, and Dr. Ken Kozak. We use mechanistic and correlative distribution models to predict the current and past (Pleistocene) distributions of P. jordani and evaluate these predictions alongside a mitochondrial phylogeny. Our analyses reveal three reciprocally monophyletic lineages that correspond to three geographic regions in the Great Smoky Mountains. The mechanistic model is consistent with genetic data, and together these results suggest that P. jordani maintained populations within its current distribution across multiple glacial cycles by tracking suitable microclimates via small changes in elevational range. I expand upon these findings in Chapter 2 by investigating geographic and demographic changes over the course of P. jordani's diversification. I find that divergence within lineages corresponds to mid- to late-Pleistocene glaciations when populations shifted to lower elevations. Effective population sizes were relatively constant over time, indicating long-term persistence and stability of populations even as distributions were shifting in response to glacial cycles. Phylogeographic reconstructions show that the range of ancestral P. jordani was in the east-central Great Smoky Mountains and populations subsequently expanded, predominantly to the west along the main ridgeline. These results suggest that topography and niche conservatism have been the main constraints on the geographic distribution of P. jordani through time. In Chapter 3, I synthesize results of the two previous chapters, along with new results based on microsatellite data, to establish conservation priorities for P. jordani. Microsatellite analyses reveal three genetic clusters that are partially congruent with phylogeographic patterns based on other markers, but show an additional genetic break in the western distribution. I propose that P. jordani comprises three evolutionarily significant units that reflect the patterns inferred from different genetic markers, ecological niche models, and historical distributions. My results highlight the importance of integrating information from multiple data sources when devising conservation and monitoring strategies for species that may be threatened by climate change. Each chapter of this dissertation will be submitted to a different scientific journal, as indicated in the footnotes at the beginning of each chapter; any variations in formatting within chapters reflect the specifications of the different journals.