Date of Award

Summer 2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biology

First Advisor

Dr. Jeffrey R. Johansen

Abstract

Contact zones between species, subspecies, or incipient lineages offer important insights into the processes that maintain reproductive isolation. Plethodon cinereus, a highly abundant and wide-ranging terrestrial salamander found in the northeast United States and southeast Canada, provides an excellent model system for studying secondary contact zones. Using mtDNA, six distinct clades have been identified across the range of P. cinereus. Populations of two such clades, the Ohio (OH) clade, which dispersed through central Ohio following receding glaciers of the last glacial maximum, and the Pennsylvania (PA) clade, which dispersed through Pennsylvania and then west through northern Ohio, can be found approximately 9.4 km apart in Lorain County, Ohio. I analyzed 268 tissue samples from 25 sites along a north-south transect following the Black River between two populations with known mitochondrial clade assignment (OHnorth and PA-south clades). Ten microsatellite loci and mtDNA haplotypes were examined to characterize the genetic structure of the contact zone. Twenty-three sample sites contained only members of the PA clade, and two sites at the northern extent of the transect including the known OH clade population contained a mixture of members of both the OH and PA clades. Population structure from microsatellite data suggests a single parental population across most of the transect, with possible evidence of admixture in sites further south; however, this structure is not concordant with mtDNA clade membership. All individuals at the site exhibiting the most admixture in mtDNA 6 clade membership were assigned to the same genetic cluster of the two groups identified based on microsatellite data. Sex-biased dispersal could contribute to the mito-nuclear discordance, but more data are necessary to test this hypothesis and determine if geographic barriers also contribute to population structure. My results suggest that the contact zone extends northward toward Lake Erie, as well as west of the present sampling area, and should be further sampled to quantify the structure of the genetic cline between these two clades.

Available for download on Wednesday, August 15, 2018

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