Genetic (RAPD) diversity in Peromyscus maniculatus populations in a naturally fragmented landscape

We assessed the effects of long-term habitat fragmentation on genetic (rand om amplified polymorphic DNA) diversity in 11 Peromyscus maniculatus popula tions in the Lake Superior watershed. We analysed genetic structure at two spatial scales and the effect of island size and isolation on genetic diver sity. At the regional scale, island populations differed from mainland popu lations (F-ST = 0.36), but mainland populations did not differ from each ot her (F-ST = 0.01). At the local scale, populations of the main island of Is le Royals differed from adjacent islet populations (P < 0.001; Monte Carlo approximation of Fisher's exact test), but not from each other (combined P = 0.63). Although geographical distance and genetic distance were positivel y correlated (P < 0.01; Mantel test), cluster analysis revealed some incons istencies. Finally, genetic diversity was inversely related to isolation (P = 0.01), but had an unexpectedly negative relationship with island area (P = 0.03). The genetic structure of P. maniculatus populations in portions o f the Lake Superior watershed appears to have been affected by long-term ha bitat fragmentation.