Microsatellite variation and population structure of the moor frog (Rana arvalis) in Scandinavia

Several recent studies have found amphibian populations to be genetically highly structured over rather short geographical distances, and that the rate of genetically effective dispersal may differ between the sexes. However, apart from the common frog (Rana temporaria) little is known about the genetic structuring and sex-biased dispersal in northern European amphibians. We investigated the patterns of genetic diversity and differentiation within and among Scandinavian populations of the moor frog (Rana arvalis) using microsatellite markers. The genetic diversity within local R. arvalis populations was not a simple linear negative function of latitude but a convex one: genetic diversity peaked in mid-latitude populations, and declined thereafter dramatically towards the north. The average degree of genetic differentiation among populations (F(ST) = 0.14) was lower than that observed for the common frog (F(ST) = 0.21), though the pattern of isolation by distance was similar for both species. Contrary to common frogs, no evidence for female-biased dispersal was found. The results reinforce the view that amphibian populations are--in general--highly structured over relatively small geographical distances, even in comparatively recently colonized areas.