No founder effects observed in rapidly expanding Peromyscus leucopus populations in Michigan’s Upper Peninsula

As species shift their distributions and establish new populations in response to climate change, maintaining connectivity with historical populations is important for genetic diversity and population viability. Populations of Peromyscus leucopus (Rafinesque, 1818) have been expanding into the Upper Peninsula (UP) of Michigan since the 1980’s, with the current range of P. leucopus extending more than 200 km from its original range in Wisconsin. To observe whether this rapid expansion of P. leucopus resulted in founder effects, five populations across the UP were sampled to determine if genetic or morphological variation was reduced in newer populations. The analyses produced three conclusions that were contrary to our predictions: the genetic structure of the UP populations sorted into two expansions (one from the west originating in Wisconsin, one from the east originating primarily in the Lower Peninsula), these expansions were supported by multiple introductions, and all populations across the UP were genetically well connected. Geometric skull shape was affected by the population of origin, even when accounting for differences in haplotype grouping. This robust genetic connectivity is likely bolstered by human-mediated transport, which has allowed P. leucopus to colonize the UP more quickly than would be possible by natural means.