Freshwater mussels (Bivalvia: Unionidae) from the rising sun (Far East Asia): phylogeny, systematics, and distribution

Abstract

Freshwater mussels (Bivalvia: Unionidae) is a diverse family with around 700 species being widespread in the Northern Hemisphere and Africa. These animals fulfill key ecological functions and provide important services to humans. Unfortunately, populations have declined dramatically over the last century, rendering Unionidae one of the world's most imperiled taxonomic groups. In Far East Asia (comprising Japan, Korea, and Eastern Russia), conservation actions have been hindered by a lack of basic information on the number, identity, distribution and phylogenetic relationships of species. Available knowledge is restricted to studies on national and sub-national levels. The present study aims to resolve the diversity, biogeography and evolutionary relationships of the Far East Asian Unionidae in a globally comprehensive phylogenetic and systematic context.We reassessed the systematics of all Unionidae species in the region, including newly collected specimens from across Japan, South Korea, and Russia, based on molecular (including molecular species delineation and a COI + 28S phylogeny) and comparative morphological analyses. Biogeographical patterns were then assessed based on available species distribution data from the authors and previous reference works.We revealed that Unionidae species richness in Far East Asia is 30% higher than previously assumed, counting 43 species (41 native + 2 alien) within two Unionidae subfamilies, the Unioninae (32 + 1) and Gonideinae (9 + 1). Four of these species are new to science, i.e. Beringiana gosannensissp. nov., Beringiana fukuharai sp. nov., Buldowskia kamiyai sp. nov., and Koreosolenaia sitgyensis gen. & sp. nov. We also propose a replacement name for Nodularia sinulata, i.e. Nodularia breviconcha nom. nov. and describe a new tribe (Middendorffinaiini tribe nov.) within the Unioninae subfamily. Biogeographical patterns indicate that this fauna is related to that from China south to Vietnam until the Mekong River basin. The Japanese islands of Honshu, Shikoku, Kyushu, Hokkaido, and the Korean Peninsula were identified as areas of particularly high conservation value, owing to high rates of endemism, diversity and habitat loss. The genetically unique species within the genera Amuranodonta, Obovalis, Koreosolenaia gen. nov., and Middendorffinaia are of high conservation concern.

Integrative taxonomy, biogeography and conservation of freshwater mussels (Unionidae) in Russia

“…(2) Eastern Palearctic (East Asian) Subregion covers the Amur Basin, rivers east of the Lena Basin, coastal rivers of the Okhotsk and Japan Sea drainage basins, and the North Pacific Islands (Sakhalin and Kuriles). Beyond Russia, this subregion extends throughout Mongolia, Korea, continental China, Japan, Taiwan, Hainan Island south to central Vietnam 44,69,70 . In Russia, this subregion is inhabited by 10 native species: Amuranodonta kijaensis, Beringiana beringiana, Buldowskia suifunica, B. shadini, Cristaria plicata, Lanceolaria grayii, Middendorffinaia mongolica, Nodularia douglasiae, Sinanodonta lauta, and S. schrenkii.…”

“…(2.2) Amur Province covering the Amur Basin and small rivers surrounding its mouth is the most species-rich freshwater system in Russia, with seven native species. Most species have vast distribution ranges throughout East Asia to South Korea (Buldowskia shadini and Sinanodonta schrenkii), Yangtze Basin in eastern China (Lanceolaria grayii) or even northern Vietnam (Cristaria plicata and Nodularia douglasiae) 44 , while Amuranodonta kijaensis and Middendorffinaia mongolica seem to be endemic lineages to this province 44 , partly spreading to the adjoining transition zone (see below).…”

“…Its fauna represents a mix of Amur, Korean, Japanese, and Chinese elements, i.e. Middendorffinaia mongolica (Amur), Nodularia douglasiae (eastern China, Korea, Japan, and northern Vietnam), Sinanodonta schrenkii (Amur and Korea), and S. lauta (Korea and Japan) 44 . Buldowskia suifunica seems to have a narrow range restricted to the BTZ, but it can also inhabit North Korea and northeastern China (e.g.…”

“…Besides these three species, generalist taxa with a broad distribution crossing a variety of drainage divides predominate in the country's fauna. Furthermore, the fauna of the Eastern Palearctic Subregion in Russia is strongly influenced by Japanese (Beringiana beringiana and Sinanodonta lauta) 43,44 , Korean (Buldowskia shadini and Sinanodonta schrenkii) 44,50 , and Yangtze (Cristaria plicata, Lanceolaria grayii, and Nodularia douglasiae) 43,44,53 lineages. This biogeographic pattern strongly differs from that in the Yangtze, Mekong and Irrawaddy basins, in which the proportion of single-basin and even intra-basin endemic lineages is much higher, with only a few widespread species 53,69,[77][78][79][80][81] .…”

“…Lanceolaria grayii inhabits Lake Khanka, Ussuri Basin, and Lower Amur (Figs. 4D, 6A and Table 1), representing the most northern enclave for this remarkable lineage of the Yangtze Basin fauna44,53 .…”