Investigating the genetic variation and structure of a native unionid mussel in the Laurentian Great Lakes following an invasion of dreissenid mussels

Despite massive population declines in the open waters of Lake St. Clair due to invasive dreissenid mussels, the St. Clair River Delta has persisted as a refuge habitat for native unionid mussels. This study was conducted to determine how Dreissena-induced population declines might have impacted the genetic population structure of native unionid species. Nine variable microsatellite markers were used to assess the genetic population structure of the Fatmucket mussel (Lampsilis siliquoidea) across 18 sites (n = 341 individuals) within the delta and four of its tributaries. Results indicate that Fatmuckets within the various bays of the St. Clair Delta and tributaries show limited genetic differentiation by geographic distance but still represent a single population with evidence of recent gene flow, little differentiation among sampling sites, relatively high allelic richness at all sites, and little evidence supporting a recent genetic bottleneck. The Fatmucket is the most common species found in the delta and poor genetic health and connectivity of this species might have indicated a dire situation for less common and imperiled species found in the same habitats. Because this did not appear to be the case, little can be assumed about other mussel species.