Genetic Monitoring Suggests Increasing Structure Following Recolonization by Fishers

Population bottlenecks, fragmentation, and isolation can have lasting effects on population genetic structure by decreasing diversity and increasing differentiation among regions. Fishers (Pekania pennanti) were extirpated from many regions of Ontario, Canada, in the early twentieth century because of overharvest, habitat loss, and predator control, although the species has since recolonized much of its former range. Between 2001 and 2003, the recolonized population could be split into several genetically distinct clusters likely corresponding to historical trapping refuges. We reassessed the genetic diversity and population structure of fishers approximately 10 years after recolonization to determine whether homogenization had occurred among genetic clusters, and whether hypothesized northward migration had continued following recolonization of southeastern Ontario by fishers from the Adirondack Mountains of New York, USA. We found no significant changes in the uppermost level of genetic structure but did find evidence of increased lower-level structure and decreased migration throughout the province, contrary to our hypothesis. This may be indicative of a reduction in fisher density or could be due to the population reaching a migration-drift equilibrium following a period of rapid expansion. Our results highlight the potential importance and utility of continued genetic monitoring following local extirpation and recolonization. Conservation managers can use periodically sampled population genetic information to adapt and update management strategies.