Unusual geographic pattern of interpopulation variation in a spring snail Bythinella (Gastropoda: Prosobranchia)

Allozyme polymorphism, mean gene diversity, and a variety of pairwise genetic distances, theta and Nm were analysed for 20 populations of the spring snail Bythinella from Central Europe. Pairwise Mahalanobis' distances for morphological characters and geographic distances were also computed. Contrary to prior assumptions, the level of polymorphism was considerable, and correlations were found to be statistically significant between the genetic and geographic distances, as well as between Mahalanobis' and geographic distances. The present high level of isolation of local populations of the previously amphibious and continuously distributed snail is postulated to be due to a shift in climate and in the snail's habitat preference.