Taxonomy and Distribution of Freshwater Pearl Mussels (Unionoida: Margaritiferidae) of the Russian Far East

<div><p>The freshwater pearl mussel family Margaritiferidae includes 13 extant species, which are all listed by IUCN as endangered or vulnerable taxa. In this study, an extensive spatial sampling of <i>Margaritifera</i> spp. across the Russian Far East (Amur Basin, Kamchatka Peninsula, Kurile Archipelago and Sakhalin Island) was conducted for a revision of their taxonomy and distribution ranges. Based on their DNA sequences, shell and soft tissue morphology, three valid species were identified: <i>Margaritifera dahurica</i> (Middendorff, 1850), <i>M</i>. <i>laevis</i> (Haas, 1910) and <i>M</i>. <i>middendorffi</i> (Rosén, 1926). <i>M</i>. <i>dahurica</i> ranges across the Amur basin and some of the nearest river systems. <i>M</i>. <i>laevis</i> is distributed in Japan, Sakhalin Island and the Kurile Archipelago. <i>M</i>. <i>middendorffi</i> was previously considered an endemic species of the Kamchatka. However, it is widespread in the rivers of Kamchatka, Sakhalin Island, the Kurile Islands (across the Bussol Strait, which is the most significant biogeographical boundary within the archipelago), and, likely, in Japan. The Japanese species <i>M</i>. <i>togakushiensis</i> Kondo & Kobayashi, 2005 seems to be conspecific with <i>M</i>. <i>middendorffi</i> because of similar morphological patterns, small shell size (<100 mm long) and overlapped ranges, but it is in need of a separate revision. Phylogenetic analysis reveals that two NW Pacific margaritiferid species, <i>M</i>. <i>laevis</i> and <i>M</i>. <i>middendorffi</i>, formed a monophyletic 18S rDNA clade together with the North American species <i>M</i>. <i>marrianae</i> and <i>M</i>. <i>falcata</i>. The patterns that were found in these <i>Margaritifera</i> spp. are similar to those of freshwater fishes, indicating multiple colonizations of Eastern Asia by different mitochondrial lineages, including an ancient Beringian exchange between freshwater faunas across the Pacific.</p>