Doctor of Philosophy (PhD)
The southeastern United States has a dynamic geologic history. Mountain range uplift, sea level fluctuations, and river basin evolution have shaped species geographic distributions in the region. My dissertation objectively identifies amphibian species with highly fragmented distributions in the Southeast (Chapter 2) and examines the phylogeographic history of one of those species, Plethodon serratus. This salamander species has a widely disjunct range across five regions: the Appalachians, the Ozarks, the Ouachitas, and two allopatric sites in Louisiana. Analyses of mitochondrial and nuclear loci (Chapter 3) showed that P. serratus is comprised of multiple genetic lineages, and the five regions are not reciprocally monophyletic. Instead, there was evidence of historical gene flow between one of the Louisiana sites and the Ouachitas. Niche and paleodistribution modeling results suggested that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species. Using a large next-generation sequencing data set of ultraconserved elements (Chapter 4), I estimated a fully resolved species tree that confirmed the non-sister relationship of the two Louisiana populations. I successfully generated this data set without modifying the established laboratory protocols; this is an important note, as large genomes can present challenges for next-generation sequencing. I found that P. serratus has a genome size of 21 pg (Chapter 5) and that this species, along with its closest relatives, has undergone genome size reduction since diverging from the ancestor of Plethodon. This dissertation demonstrates that established methods of next-generation sequencing can be used in studies of large-genome salamander phylogeography. This is especially important, as many salamander populations are declining in the face of habitat loss and climate change. Plethodon serratus is only one of many amphibian species in the Southeast with fragmented ranges. Future research on the biogeography of these organisms will be crucial to conservation.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Newman, Catherine Elizabeth, "Evolutionary History of a Large-Genome Salamander Across Five Disjunct Regions of the Southeastern United States" (2017). LSU Doctoral Dissertations. 4315.
Austin, Christopher C