Genetic consequences of ice ages for a holarctic rodent: phylogeography and post-glacial colonization of the tundra vole, Microtus oeconomus, in Beringia

Abstract

Periodic glacial advances during the Pleistocene fragmented and displaced populations, while lowered sea levels permitted a biotic interchange between Asia and North America via the Bering Land Bridge. The tundra vole (Microtus oeconomus), a recent colonizer of North America, is a good model for studying the genetic consequences of these events. Variation in Mitochondrial (cytochrome b and control region) and nuclear (ALDH1) markers were examined within the context of Beringia's paleoclimatic history to examine the role of glaciations in driving differentiation and structuring patterns of genetic diversity. Genealogical relationships among genetic lineages were also assessed to elucidate probable paths of transberingian gene flow and post-glacial colonization. A deep phylogeographic break in western Beringia separates Beringian and Central Asian clades and may have been initiated by glacial vicariance. Population genetic structure within the Beringian clade has largely been determined by an historical reduction in genetic diversity and subsequent local differentiation. Serial bottlenecking during post-glacial colonization had minor effect, if any. Female-mediated gene flow among populations has been minimal since the last glacial maximum, but affinities among populations in Siberia and Alaska suggest two latitudinally partitioned routes of gene flow across the Bering Land Bridge. Also, post-glacial colonization of heavily glaciated southcoastal Alaska probably proceeded along coastal routes from the west after glacial recession.