Molecular Markers Reveal Genetic Contamination of Endangered Freshwater Pearl Mussels in Pearl Culture Farms in Japan

Abstract

Phylogenetic analyses using mitochondrial DNA (Cox2-Cox1) and nuclear DNA (ITS1) were performed on a critically endangered freshwater pearl mussel, Hyriopsis schlegeli, endemic to Lake Biwa, Japan, and a closely related Chinese species H. cumingii, which was introduced to Japan approximately 30 years ago. Using samples of typical H. schlegeli and H. cumingii, clear genetic differences between the two species were recognized in both molecular markers. Surveys of the genetic compositions of freshwater pearl mussels showed evidences of hybridization between the two species in culture farms in Lakes Kasumigaura and Biwa. Given that pearl culture farms are not completely isolated from natural water systems in Lake Biwa, these findings suggest that native H. schlegeli might be threatened by hybridization with H. cumingii. The wild population in Lake Anenuma, Aomori Prefecture, Japan would be the only remaining ‘pure' population of H. schlegeli free from hybridization and therefore be very important for conservation, although it originated from escaped cultured mussels.