New microsatellite markers for Ellipse, Venustaconcha ellipsiformis (Bivalvia: Unionidae), with notes on optimal sample size and cross-species amplification.

Venustaconcha ellipsiformis (Unionidae) is a freshwater mussel species inhabiting small to medium streams of the Midwestern United States; however, its occurrence is rather sporadic and populations are often isolated. Due to anthropogenic habitat degradation and water pollution, this species is designated as some sort of conservation status in many states. To prioritize conservation strategies, highly variable genetic markers are necessary to assess population genetic structure and potential genetic erosion of V. ellipsiformis. Using whole genome sequence data, we developed and characterized microsatellite markers for V. ellipsiformis. Among 23 tetranucleotide loci tested, 14 loci were consistently amplified and showed polymorphism. Analyses performed on three populations in the upper Mississippi River basin showed that the number of alleles per locus ranged from 2 to 11 and the observed heterozygosity varied from 0.15 to 0.75. Based on genotypic and allelic rarefaction curves, these loci had adequate statistical power to genetically discriminate between individuals and the sample size was large enough to capture most alleles available in the populations at most loci. Finally, cross-species screening of the loci successfully amplified and showed polymorphism in six species in the tribe Lampsilini. The microsatellite loci developed in this study provide a valuable addition to extant genetic markers for freshwater mussels and can be useful to provide high-level resolution of population genetic parameters for V. ellipsiformis. Such information will be of great value for resource managers developing and prioritizing conservation strategies for imperiled mussel species.