Genetic diversity in the threatened freshwater mussel Lampsilis powellii

North America is home to the greatest share of the world's freshwater mussel diversity; however, over 70% of its ~300 species are endangered or threatened. Lampsilis powellii, the Arkansas Fatmucket, is endemic to Arkansas and now restricted to upstream reaches of the Ouachita and Saline rivers, but the species is declining within this small range. Conservation actions such as augmenting or reintroducing populations may be necessary, but they require knowledge of the distribution of genetic variation within and among extant populations. We analyzed population structure between the South Fork Ouachita River and Saline River using a 607 base pair region of the mitochondrial COI gene and 14 microsatellites designed for Lampsilis abrupta. COI sequences showed little variation and the most common haplotype was present in both rivers. Our mtDNA sequences were indistinguishable from those of L. siliquoidea deposited on GenBank, but we were unable to make conclusions about the taxonomic distinctiveness of L. powellii. Microsatellites showed heterozygote deficiency for most loci and revealed little evidence of population structure between the two rivers. Overall, our results show low genetic diversity in L. powellii, which may reflect its small population size due to its long history of geographic isolation compounded by anthropogenic habitat destruction and fragmentation. Further genetic analyses of lampsiline taxa is needed to establish species limits for Lampsilis in the Interior Highlands.