Population genetics of freshwater pearl mussel (Margaritifera margaritifera) in central Massachusetts and implications for conservation

1) The freshwater pearl mussel Margaritifera margaritifera is an ecologically-important globally-endangered species, yet little is known about its biodiversity and population genetics in North American populations. This study focused on M. margaritifera from six locations within two central and eastern Massachusetts, USA, stream systems to better understand the historical impact of damming and habitat fragmentation on local population structure and genetic diversity.2) Approximately 300 informative single nucleotide polymorphisms (SNPs) were generated from 59 individuals across six geographic locations, using the RAD-seq approach. Genotypes were also gleaned from publicly available RNA-seq data of 23 French M. margaritifera samples.3) Population structure predictions using Discriminant Analysis of Principle Components (DAPC) and fastStructure both indicate the existence of a single genetic population in central and eastern Massachusetts, and a clear separation from French individuals. This observation is further supported by frequency-based population genetics calculations, which indicate near-complete admixture and a high number of migrants between Massachusetts sites.4) These results suggest that the effects of habitat fragmentation from damming in the past century have not radiated through the Massachusetts population of M. margaritifera, potentially due to the species' long lifespan and generation time. However, the Massachusetts genetic population has similar levels of genetic diversity compared to endangered populations in Europe, and conservationists should consider these factors when creating management plans.