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BROAD SCALE PHYLOGEOGRAPHY OF THE BANDED WATER SNAKE, NERODIA FASCIATA**

Abstract

Geographic barriers to dispersal are a major cause of reproductive isolation, which can lead to divergence and speciation. However, the interaction of different taxa with these barriers varies across taxonomic and geographic scales. In the southeastern coastal plain, several phylogeographic patterns have emerged in response to shared landscapes. For instance, during the last glacial maximum, many species were restricted to “refugia” in the southern U.S. Isolation is thought to have persisted during interglacial periods by major rivers made wider by melting glacier water allowing for expansion north and south but restricting gene flow east and west. There is also evidence that during interglacial periods some species were isolated to peninsular Florida which had been rendered an island by high sea levels, causing deep divergences between these populations and the rest of their species. Herein, we test these hypotheses in the banded water snake (Nerodia fasciata), whose range spans several such potential biogeographic barriers. We will use both nuclear and mtDNA to test for phylogeographic structure and evaluate the impact of geographic barriers (i.e., major drainage systems and glacial refugia) on diversification of this group. This study will test the validity of three named subspecies of N. fasciata and determine if peninsular Florida and the Mississippi and Apalachicola Rivers have acted as biogeographic barriers for this species and how glacial refugia played a role in their evolution. Quantifying diversification across landscapes will promote the understanding of broad scale evolutionary processes.

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