Organisms with complex life histories and unusual modes of genome inheritance can present challenges for phylogenetic reconstruction and accurate assessment of biological diversity. This is particularly true for freshwater bivalves in the family Unionidae because: (1) they have complex life cycles that include a parasitic larva and obligate fish host; (2) they possess both a male and female mitochondrial genome that is transmitted through doubly uniparental inheritance (DUI); and (3) they are found in riverine habitats with complex hydrogeological histories. Examination of mitochondrial DNA (mtDNA) sequences, conglutinate morphology, and host fish compatibility of the western fanshell Cyprogenia aberti (Conrad, 1850) revealed significant character variation across its range. Although variation was correlated among the different data sets and supports discrete groups, these groups did not always correspond to geographically isolated populations. Two discrete mtDNA clades exist sympatrically within most C. aberti populations, and these same clades are also diagnosed by at least one morphological character, egg color. The surprisingly high genetic distance (14.61%–20.19%) between the members of these sympatric clades suggests heritance infidelity of the two different mitochondrial genomes. This hypothesis was tested and falsified. More general patterns in geography were observed in host fish compatibility. Populations of C. aberti from the major river systems differed in their ability to utilize fish species as hosts. These differences in reproductive traits, which are presumably genetically based, suggest that these populations are not ecologically exchangeable with one another and represent biological diversity not previously recognized within Cyprogenia Agassiz, 1852.
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Vol. 95 • No. 2