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Species distributions and population genetic structure are determined by landscape history and biological characteristics of an organism. Pleistocene glaciations affected species distributions and freshwater drainage patterns. Extensive work on the biogeography of fish has determined the effects of glaciations on genetic population structure and described recolonization routes from glacial refugia. Freshwater mussels are intimately tied to fish because larvae are largely obligate parasites on fish. Dispersal via hosts has likely led to similar patterns in genetic structure and distributions of mussels and fish. I quantified genetic diversity using mitochondrial DNA and allozymes to determine genetic population structure and infer evolutionary history for Cumberlandia monodonta — an endangered species (Chapter 2). There was a lack of genetic structure and evidence of high gene flow. The phylogeny indicated isolation in two glacial refugia followed by post-Pleistocene dispersal of two lineages range-wide. The distribution of Lampsilis cardium, a non-endangered species, spans glaciated and non-glaciated areas. Genetic diversity was quantified in northern and souther