An evaluation of the genetic structure of mapleleaf mussels (Quadrula quadrula) in the Lake Erie watershed

Physical barriers, habitat fragmentation, invasive species and geographic distance have isolated remnant populations of unionids in Great Lakes coastal refuges. Dreissenid species (Dreissena polymorpha and Dreissena rostriformis bugensis) may be the greatest threat to the survival of unionids in the Great Lakes since their introduction in the late 1980s and early 1990s; however, native unionids remain in coastal habitats of western Lake Erie. One of the most abundant unionid species in Lake Erie, Quadrula quadrula, was collected along coastal areas within the lake and from three tributaries, the Maumee River, Huron River (Ohio), and Grand River (Ontario, Canada) and genotyped at six polymorphic microsatellite loci to determine population structure. There was evidence of genetic differentiation by geographic distance, and genotypes clustered into three geographic regions: Lake Erie, the Maumee River, and the Grand River. Lack of fine-scale genetic differentiation, admixture among these regions, and significant isolation by distance, indicate connectivity and are consistent with a stepping-stone model of divergence across the lake and its tributaries. A diverse gene pool remains should Q. quadrula be able to repopulate more of their historic distribution across the region, but studies of other unionid species are needed to determine whether low levels of differentiation among lake populations or divergence from tributary populations is a common pattern.