Management Implications of Post-Glacial Colonization Routes and Genetic Structure for Freshwater Mussels (Unionidae) In the Great Lakes

Declines in North American freshwater mussel (Unionidae) populations have left 70% of species vulnerable to extinction. Continuous population declines in the last century have resulted in dire need for conservation actions; however, a good understanding of patterns in genetic population structure often inhibits conservation strategies and management. Two important hypothesized routes of entry for aquatic organisms into Laurentian Great Lakes at the end of the Wisconsin glaciation followed the paths of the Wabash-Maumee outlet and the Chicago-Illinois River outlet. We have tested these hypotheses and compared the post-glacial origin of three relatively common freshwater mussel species in the Great Lakes basin. We genotyped microsatellite DNA markers to analyze genetic diversity from three relatively common unionids in the Great Lakes and beyond and interpreted their patterns of genetic population structure. Our findings indicate that the pattern of post-glacial colonization varies among species with some species entering following Chicago-Illinois River outlet and others following multiple routes. Understanding these patterns for unionids in the Great Lakes will help formulate evolutionarily sound management guidelines and provide insight for augmenting and re-establishing populations of species of conservation concern.