FINE-SCALE POPULATION STRUCTURE IN THE WOOD FROG (RANA SYLVATICA) IN A NORTHERN WOODLAND

We investigated the genetic structure of wood frog (Rana sylvatica) populations in a woodland habitat around Lake Itasca, Minnesota, USA. Based on published studies of wood frog movement patterns, we expected to find genetic differentiation at inter-population distances exceeding a few kilometers. We sampled 10 populations separated by 95 m to 9.6 km. Of five microsatellite loci developed for a study of R. sylvatica in North Dakota, only three were polymorphic in the Itasca sample. We found some evidence for statistically significant differences among populations, with the greatest magnitude estimates of F_ST derived from comparisons involving the most isolated populations. The smallest geographic distance associated with a statistically significant genetic difference was 1070 m, but most populations were very similar in allele frequencies, even at distances greater than several kilometers. Small sample sizes and the small number of loci limited the strength of any conclusions regarding fine-scale population structure. Itasca populations were significantly different than populations from Nelson County, North Dakota, a distance of over 200 km, with F_ST estimated at about twice the largest pairwise estimates among Itasca samples. Even at this distance, however, there were substantial similarities in the overall pattern of allele frequencies at four of the five loci.