We investigate population genetic structuring in Margaritifera falcata, a freshwater mussel native to western North America, across the majority of its geographical range. We find shallow rangewide genetic structure, strong population-level structuring and very low population diversity in this species, using both mitochondrial sequence and nuclear microsatellite data. We contrast these patterns with previous findings in another freshwater mussel species group (Anodonta californiensis/A. nuttalliana) occupying the same continental region and many of the same watersheds. We conclude that differences are likely caused by contrasting life history attributes between genera, particularly host fish requirements and hermaphroditism. Further, we demonstrate the occurrence of a ‘hotspot’ for genetic diversity in both groups of mussels, occurring in the vicinity of the lower Columbia River drainage. We suggest that stream hierarchy may be responsible for this pattern and may produce similar patterns in other widespread freshwater species.

MargPops48_UTMsThis is a list of the spatial coordinates for the populations and subpopulations referenced in the paper.GAEPopReg20Nov12This is a file of raw microsatellite genotypes by population for Margaritifera falcata in the western United States. The data are in GenAlEx format.Margaritifera falcata COI-F mitochondrial haplotypesThis is a spreadsheet delineating mitochondrial haplotypes and associated GenBank accessiong numbers for a set of Margaritifera falcata samples from the western United States.MargHaplos19Oct12_Dryad.xlsx