Molecular and morphological perspectives on post-glacial colonization of Clethrionomys rutilus and Clethrionomys gapperi in Southeast Alaska

Abstract

Pleistocene events had a significant impact on the geographic distributions of high latitude organisms. Recently deglaciated, Southeast Alaska has been colonized by two species of red-backed voles, clethrionomys rutilus and C. gapperi. With distinct biogeographic histories, post-glacial colonization of C. rutilus and C. gapperi into this region would have occurred by different routes. Variation in the mitochondrial cytochrome b gene, the MYH2 nuclear intron, and the post palatal bridge were assessed to examine phylogeographic patterns of these two species, and a proposed contact zone in southeast Alaska. Low, but consistent, levels of sequence divergence of the cytochrome b gene were found among four endemic populations, which corresponded with the complex topography of southeast Alaska. Asymmetrical introgression of the mitochondrial genome diagnostic of C. rutilus was observed in C. gapperi. Post glacial contact resulting from the retreat of the Cordilleran and Laurentide ice sheets has apparently led to the formation of this hybrid zone.