Human activities such as dam construction, stream channelization, pollution, and introduction of invasive species have led to a freshwater biodiversity crisis. One of the most imperiled taxa occurring in freshwater ecosystems are freshwater mussels. Habitat loss and degradation has led to a decline in the abundance and distribution of freshwater mussels in North America and many populations have become smaller and more isolated. Smaller, more isolated populations are more likely to exhibit a reduction in genetic diversity which could render species incapable of adapting to a changing environment. Considering recent fragmentation, it is possible that some species have lost essential genetic connectivity between populations. Effective management strategies of these species must include reestablishment of historical genetic connectivity. This study aims to elucidate whether human activities have impacted genetic connectivity previously found in the Sheepnose mussel (Plethobasus cyphyus) by using microsatellite markers and mitochondrial sequences.

166 Sheepnose mussel samples collected across the Midwestern United States were used to determine population structure, population genetic diversity, contemporary and historical migration rates, and changes in population size. Analyses of microsatellite and mitochondrial data indicate that Sheepnose populations exhibit a high degree of genetic diversity. Population structure analyses reveal that the Sheepnose currently consist of two genetic populations, one population occupying the Upper Mississippi River Basin and the other in the Ohio River Basin. Estimated contemporary migration rates indicate that migration between sampling locations is occurring within (although at very low rates) and not between drainage basins. Estimates of historical migration rates indicate that significantly more migration was occurring within and between drainage basins, although also at very low rates. Population bottlenecks were not detected at any of the sample sites and all sites except the Wisconsin River exhibited the signature of population expansion. Results of this study indicate that human activity has effectively reduced genetic connectivity between populations of Sheepnose. Surprisingly, each population has retained a considerable amount of genetic diversity, so it is likely that the full effect of isolation has not been realized yet. Conservation managers should seek to reestablish connectivity between Sheepnose within river basins before genetic diversity is lost indefinitely.