Genetic variation at the species and population levels in the Rocky Mountain ridged mussel (Gonidea angulata)

Freshwater mussels in western North America are threatened by water diversions, climate change, loss of required host fish, and other factors, and have experienced marked decline in the past several decades. All four of the primary lineages (potentially species) of freshwater mussels in the western U.S. and Canada are widespread and have somewhat generalist host fish requirements. Of these lineages, perhaps the most poorly understood and of greatest conservation concern is Gonidea angulata (Rocky Mountain ridged mussel). Gonidea is a monotypic genus occurring only in the western continental U.S. and southern Canada. Here we describe the patterns of genetic variation across the species range, including several populations in the Okanagan Valley at the northern edge of the range. We detected only ten mitochondrial cytochrome oxidase I haplotypes, three of which ere commonly found across major hydrologic basins, and the remainder of which were basin-specific variants. Haplotypes differed by a maximum of 5 of 537 nucleotides. New microsatellite loci were developed for G. angulata as a part of this study. Data from these microsatellite loci indicated that the population in the Chehalis River, Washington, was distinct from other locations, and that the Okanagan lake population was somewhat diverged from the remaining populations in the Columbia River and Klamath Lake. Only low levels of inbreeding were detected, in contrast to previous findings in Margartifera falcata, suggesting that hermaphroditism is not common. The population with the least diversity, according to microsatellite data, was the northernmost known population in Okanagan Lake We discuss the biogeographic and conservation implications of our findings.