| Pleistocene glacial-interglacial cycles resulted in population isolation that led to inter- and intra- specific genetic divergence in many North American species. The magnitude of isolation also influenced species response to these climatic changes and set the stage for contemporary gene flow. We can refine our understanding of species response to historical climate change by identifying regions of ice-free persistence and refugia during glacial maxima, and geographic locations and genetic dynamics of post-glacial secondary contact. This dissertation examines the role of glacial cover, geographic barriers, habitat fragmentation as a result of changes in sea level, and insularity on the contemporary genetic structure of three widespread, co-distributed, and ecologically distinct small mammals across western North America, with emphasis on the Pacific Northwest. Previous work on long-tailed voles (Microtus longicaudus), northwestern deer mice (Peromyscus keeni), and dusky shrews (Sorex monticolus) was used to formulate hypotheses of geographic distribution of genetic variation, timing of divergence, and regions of glacial persistence. This dissertation uses multilocus genetic data and historical climatic conditions to address these hypotheses. I identify regions of glacial persistence, the effects of historical sea levels on island connectivity, and regions of post-glacial secondary contact of divergent lineages within M. longicaudus, P. keeni and S. monticolus. Additionally, I assess levels of endemism for the islands of Southeast Alaska. The collective findings of this dissertation improve our understanding of effects of historical range fragmentation and insularity on contemporary genetic diversity. |
