Genetic and ecological diversity of a rare freshwater pearl mussel Margaritifera laevis with reference to its conservation plan

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To elucidate the biological diversity and make a conservation plan for an endangered freshwater mussel. Margaritifera laevis, the genetic diversity of the local populations, habitat preference of each local population and host-parasite relationships between the glochidia of this mussel and salmonid species were examined in this study and the following results were obtained.1. Allozyme and mtDNA analyses revealed two highly divergent groups (Group A and B) with on evidence of hybridization between the groups which were sympatrically distributed, suggesting the existence of reproductive isolation between them. As for genetic diversity, group A showed considerable genetic variations among populations, whereas group B showed no any genetic variation.2. Species identification of glochidia by using specific mtDNA markers indicated that the glochidia of group A parasitized only the gill of Oncorhynchus masou, whereas those of group B parasitized the gill of Salvelinus leucomaenis and S. malma.3. The field ecological survey revealed that water current and bottom substratum were important environmental factors limited to survival for the two groups of M laevis.4. To conserve the local populations of two groups of M. laevis, an active conservation plan including the maintenance of good host-parasite association and restoration of good stream bottom conditions on which the glochidia were possible to settle down was proposed in this study.