Portland State University. Department of Biology
Term of Graduation
Date of Publication
Master of Science (M.S.) in Biology
Woodland salamanders -- Pacific Northwest, Salamanders -- Pacific Northwest -- Geographical distribution, Salamanders -- Pacific Northwest -- Phylogeny
1 online resource (109 pages)
Genetic studies of amphibians often reveal substantial population structure due to either historical demographics from changing climate and geographic features over varying timeframes. Eight species of terrestrial salamanders (Family: Plethodontidae, Genus: Plethodon) reside in forests of the Pacific Northwest (PNW). Plethodon vehiculum is the most widespread and abundant terrestrial salamander in the PNW yet evolutionary studies are lacking. Using mitochondrial DNA (mtDNA) sequence data (D-loop and cytb) questions regarding the phylogeography of P. vehiculum and phylogenetics of western Plethodons are explored. Two major clades were defined in P. vehiculum, a southern clade in the Klamath-Siskiyou region and a northern clade ranging from northern Oregon to British Columbia using parsimony and maximum likelihood trees and a haplotype network. High divergence levels between the north and south clades are observed warranting further investigation into the southern clade's unique evolutionary trajectory. The northern populations were not highly differentiated with high levels of haplotype sharing, not common in other terrestrial salamander species. A large recent range expansion or high habitat connectivity for these salamanders is suggested. The Columbia River did not act as barrier to dispersal in this species, however, Vancouver Island and the population of Washington's Olympic Peninsula revealed unique haplotypes only to those areas, due to the presence of geographic barriers to dispersal and/or multiple glacial refugia. The D-loop and cytb provided evidence for recent range expansion in the northern clade.
This was the first study to incorporate all western Plethodon salamanders in a phylogenetic study. Parsimony and maximum likelihood methods offered strong support for recognized relationships among western Plethodons, however relationships between the major groups remain unhighly supported. Lack of genetic diversity in the mtDNA cytb gene in P. vehiculum is highly inconsistent with other Plethodon salamanders and highlights the importance of understanding mtDNA evolution in ectotherms. Divergence measures were used to estimate divergence times among species, dating all speciation before the Pleistocene glaciations. The southern OR clade of P. vehiculum was dated to have been separated from the northern clade at the start of the Pleistocene. The deep phylogeographic break here justifies the possibility of reclassification of the southern clade.
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Pelletier, Tara Anne, "Phylogeographic and Phylogenetic Exploration of Plethodon (Plethodontidae, Caudata) Salamanders in the Pacific Northwest" (2009). Dissertations and Theses. Paper 5590.