| Plethodon salamanders are fully terrestrial, lungless salamanders found in forested areas throughout North America. My dissertation focuses on five of these salamander species located in the Pacific Northwest (PNW). The PNW has a complex geologic history including events such as volcanism and repeated glaciations. This complexity makes studying biodiversity patterns informative as to what evolutionary processes shape current population and species structure. The five species that are the focus of my dissertation are used to learn about Plethodon salamanders in general, but because these salamanders are at different stages of divergence within and among species, they can further be used to explore methods in phylogeography, which help us better understand the process of evolution.;First, I explore demographic model selection using genetic data in P. idahoensis (Chapter 2). The best demographic model for this species is one with population divergence, expansion, and migration. Furthermore, the evaluation of Approximate Bayesian computation techniques highlights the complexities of this method for model selection in phylogeography.;Next, I test species boundaries in P. vandykei, P. larselli, and P. idahoensis (Chapter 3). Results of this study were opposite of those expected, in that the current range of the species did not accurately predict species boundaries. In other words, geographic proximity and connectivity did not produce species hypotheses that were supported by genetic data. Alternatively, distributions estimated from historical species distribution models were better predictors of current genetic patterns.;Finally, I explore range expansion dynamics in P. dunni and P. vehiculum using genetic, environmental, and morphological data (Chapter 4). Both species underwent recent rapid range expansions since the Pleistocene and share similar population structure, but one species has a much larger geographic range than the other. The best explanations for the difference in distribution between these two species are physiological tolerances and dispersal ability, while spatial sorting most likely plays a key role in the range expansion of P. vehiculum..;A better understanding of population structure, demographic history, and speciation is important for conservation purposes and a better theoretical understanding of evolutionary processes. My dissertation accomplishes both these tasks by determining the population structure, demographic history, and species boundaries in these salamanders specifically, but also by evaluating methods in phylogeography that are used to understand these processes. |
