Hybrid zones provide excellent opportunities to study evolutionary processes. By elucidating mechanisms that shape hybrid zones, we can begin to understand the role of evolutionary factors such as selection, barriers to genetic exchange, and new adaptations. The dynamic glacial events of the late Pleistocene (130,000 - 10,000 years ago) are believed to have modified geographic distributions of many high latitude organisms and created contact zones. While many of the documented post-glacial contact zones are Eurasian, phylogeographic studies in North America are demonstrating post-glacial contact following the retreat of the ice sheets. Preliminary research on a post-glacial contact zone between the northern red-backed vole (Clethrionomys rutilus) and southern red-backed vole (Clethrionomys gapperi) in southeast Alaska documented unidirectional introgression of the mitochondrial genome of C. rutilus into populations of C. gapperi. The proposed work will use additional molecular markers and morphometric tools to explore fundamental evolutionary processes in this hybrid zone. The red-backed vole contact zone is an excellent model system because the phylogeographic histories of these taxa are well known. These species contact each other over 2000 km, providing an opportunity to study interspecific dynamics at multiple localities to test for the consistency of processes that may be shaping this contact zone. Using individuals from populations across three transects of the contact zone, the study will combine morphological data, sequences of the cytochrome b, Sry, MHY2 genes, and 12 microsatellite loci to address the following questions: What is the direction of introgression? Is introgression contemporary? What are the fates of the hybrids? Are the consequences of interspecific interactions the same across multiple transects of the contact zone?
