Phylogeography and Postglacial Dispersal of Smallmouth Bass (Micropterus dolomieu) into the Great Lakes

Refugia and dispersal routes of smallmouth bass (Micropterus dolomieu) into the Great Lakes were identified using 427 mitochondrial sequences from across their native range. Overall, smallmouth bass accessed the Great Lakes via long-distance dispersal from multiple refugia, and the distribution of genetic variation reflected the consequences of vicariant, dispersal, and paleogeological events. Proximity of lakes to glacial outlets had a greater predictive power on the resulting distribution of mitochondrial diversity relative to interbasin migration. Populations in the Eastern and Interior Highlands contained the most divergent and oldest haplotypes, reflecting their role as glacial refugia and subsequent high incidence of endemicity. Lake Superior, Lake Michigan, and northern Lake Huron were colonized by bass of a single mitochondrial clade that accessed the Brule–Portage (Mississippi and St. Croix rivers) and Chicago (Illinois and Fox rivers) outlets. Lakes Huron and Erie contained admixed mitochondrial lineages in part due to numerous access points, including the Fort Wayne (Wabash and Maumee rivers), Lower Peninsula of Michigan (Grand River valley), and Kirkfield (Kawartha Lakes) outlets. In contrast, populations in Lake Ontario, Georgian Bay of Lake Huron, and the St. Lawrence River were monomorphic, indicating a single but unidentified source. These patterns were consistent with many examples from the North American freshwater ichthyofauna.