Fine-scale genetic structure of the freshwater snail Promenetus exacuous in the New York State region: the influences of historical colonization, habitat connectivity and dispersal ability

The pulmonate freshwater snail Promenetus exacuous (Planorbidae) has a widespread patchy distribution throughout much of North America, including New York State and the surrounding areas. Minimal life history information exists for the species in this region and information on its genetic diversity and structure is currently lacking for any portion of its range. We examined the species’ reproductive behaviour, genetic diversity and population structure throughout New York and western Connecticut using cytochrome c oxidase subunit I (COI) haplotypes (241 snails) and 10 microsatellite loci (312 snails). Throughout the region, P. exacuous is a single, primarily outcrossing species with relatively high within-population genetic diversity. Populations are genetically differentiated and composed of divergent COI lineages. The region was colonized after the Wisconsin glacial retreat by snails from multiple, historically isolated populations and Pleistocene events played a major role in the historical diversification of lineages. Subsequent dispersal has likely been facilitated by birds and humans, but contemporary gene flow is low, resulting in genetic differentiation even among geographically proximate sites. Our data reveal that complex interactions between historical and contemporary processes contribute to the overall patterns of genetic diversity in freshwater snails.