Mitochondrial DNA genetic structure transcends natural boundaries in Great Lakes populations of woodland deer mice (Peromyscus maniculatus gracilis)

The landscape of the Great Lakes region has been fragmented since the lakes formed starting about 20 000 years ago. Small mammals, such as deer mice (Peromyscus maniculatus (Wagner, 1845)), inhabiting the region therefore face barriers to migration and gene flow, which could complicate ongoing range shifts related to climate change. We analyzed DNA sequences for 481 base pairs of the mitochondrial D-loop to compare mouse genetic structure with the fragmented landscape and geological history of the region. Phylogenetic analyses reveal two distinct lineages of mice in the Great Lakes region. The spatial distribution of these two groups is not congruent with the fragmentation of the landscape; rather, a western group is found from Minnesota through the western Upper Peninsula of Michigan, whereas an eastern group spans southern Ontario and the rest of northern Michigan. The genetic data suggest that the eastern clade colonized Michigan through Ontario from a source shared with southern Appalachian mice, but are less informative for the western clade. Together, these findings suggest that the Great Lakes are relatively porous barriers in the long term but may still have implications for the response of small-mammal communities to climate change.