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.

Fourteen of fifteen microsatellite primers designed for Lampsilis abrupta (Eackles and King 2002) were successfully optimized in L. powellii. Forward primers for each PCR were labeled with a 5’ fluorescent tag (6-FAM, NED, PET, or VIC) for visualization.  Microsatellite loci were amplified in 10 μL reactions using GoTaq Master Mix (Promega Corp.), 0.5 μM of fluorescently-labeled forward and reverse primer, and 10 ng of DNA template carried out under the following conditions: initial denaturing at 94 °C for 2 min; 35 cycles of 94 °C for 40 s, variable annealing temperature for 40 s (Appendix A1), 72 °C for 1 min; and a final extension at 72 °C for 5 min. Fragment analysis was performed on an ABI 3730 Genetic Analyzer with LIZ600 size standard (Applied Biosystems, Inc).