Phylogeography of the freshwater mussel species <italic>Lasmigona costata</italic>: testing post-glacial colonization hypotheses.

Understanding genetic diversity across large spatial scales helps to reveal patterns of population structure. Mitochondrial DNA sequences and microsatellite loci were used to analyze the phylogeography of a common unionid species (<italic>Lasmigona costata</italic>) from the Laurentian Great Lakes and historically connected river drainages. Phylogeographic patterns were assessed to determine colonization routes into the Great Lakes following glacial recession. A suite of seven microsatellite loci were genotyped and a fragment of the mitochondrial gene COI was sequenced. Multiple analyses using microsatellite allele frequencies suggest at least two distinct genetic populations for <italic>L. costata</italic>. A total of seven hypothesized post-glacial dispersal scenarios were compared using isolation by distance to test the various dispersal models. Evidence was strongest for two post-glacial dispersal routes into the Great Lakes: one utilizing a connection between the Wabash and Maumee River watersheds, and one utilizing a connection between the Wisconsin River and Green Bay watersheds. A highly differentiated and monophyletic population of <italic>L. costata</italic> was identified in the Ozark Highlands, which may constitute a unique taxonomic entity. [ABSTRACT FROM AUTHOR]