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

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 gosannensis sp. 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

Are Cristaria herculea (Middendorff, 1847) and Cristaria plicata (Leach, 1815) (Bivalvia, Unionidae) separate species?

The number of species in the freshwater mussel genus Cristaria Schumacher, 1817 recognized from Far East Russia has varied over the last several decades. While some authors consider the occurrence of only one species, Cristaria plicata (Leach, 1815), widespread in East Asia, others, recognize two separate species Cristaria herculea (Middendorff, 1847) and Cristaria tuberculata Schumacher, 1817 from Far East Russia, distinct from C. plicata. For the present study, freshwater mussels, identified as C. herculea, were collected in the Upper Amur basin (Transbaikalia, Russia). The shell morphology and the whole soft body anatomy were analysed in detail and compared with previously published information on other Cristaria spp.. Additionally, a cytochrome oxidase subunit 1 (CO1) gene fragment was sequenced from foot tissue samples of selected animals, collected from the same region, and compared with published data. Based upon morphological similarities of glochidia and adult morphology and anatomy as well as the mitochondrial DNA sequence analysis, we consider C. herculea as a synonym of C. plicata. Further analysis of Far East Russia C. herculea and C. tuberculata specimens using both molecular and morphological characters should be carried in the future to enhance our knowledge about the taxonomy within the Cristaria genus. Moreover, a comprehensive revision of the genus Cristaria is needed, restricting the type locality and comparing topotypic specimens for both C. plicata and C. tuberculata, and including all recognized Cristaria species

Systematics and distribution of Cristaria plicata (Bivalvia, Unionidae) from the Russian Far East

The number of anodontine bivalve species placed in the genus Cristaria (Bivalvia, Unionidae) from the Russian Far East is still not stable among authors. Some recognize only one valid species C. plicata (Leach, 1815) while others accept two additional species, C. tuberculata Schumacher, 1817 and C. herculea (Middendorff, 1847). In the present study, these taxonomic doubts are addressed using analyses of mitochondrial DNA sequences and shell morphometry. No significant differences have been revealed by the COI DNA sequences or the main statistical morphometric indices from the three Cristaria forms. In the specimens analysed, changes in shell morphometry with age suggest that original descriptions of the different forms may be attributed solely to differences in age and sex. We consider that C. plicata, C. tuberculata and C. herculea from the Russian Far East should be considered as a single species, namely Cristaria plicata (Leach, 1815), with C. tuberculata and C. herculea as junior synonyms. The geographic range of Cristaria plicata and its conservation status are also presented here

The Pleistocene-Holocene aquatic molluscs as indicators of the past ecosystem changes in Transbaikalia (Eastern Siberia, Russia).

Data on the historical change of the Transbaikalian malacofauna in the Neopleistocene and Holocene is presented. Aquatic mollusc shells from archaeological excavations of the ancient settlements dating from the Neolithic period to Medieval and also from a drill hole of the Neopleistocene alluvial deposits were collected. In total eight species of bivalve molluscs from the families Margaritiferidae, Unionidae, Lymnocardiidae, Glycymerididae [marine], and two gastropod species from families Viviparidae and Planorbidae were identified. These species were aged using radiocarbon dating. It was found that the species ranged in age from more than 50.000 to 2.080-1.210 years BP. Five species inhabited the Transbaikal region which are locally extirpated today. Their disjunctive ranges in the past included southern Europe and Western and Eastern Siberia to Transbaikalia and in the east to Far East and Primorye Territory of Russia. A remarkable finding is that of the bivalve genus Monodacna, which was found very far from its native range, the Ponto-Caspian region. The time of existence and extirpation of the thermophilic species of genera Monodacna, Planorbis, Lanceolaria and Amuropaludina corresponds to cycles of the warming and cooling in Pleistocene and Holocene according to regional climate chronological scales. These species can be used as palaeoclimate indicators. Change of the regional malacofaunal species composition is connected with the natural climatochron cycles in the Pleistocene and Holocene resulting in evidence for succession. In the course of this succession, these stenothermal species became extirpated on a regional level, decreasing their global ranges

Morphological and molecular analyses of Anodontinae species (Bivalvia, Unionidae) of Lake Baikal and Transbaikalia

<div><p>The diversity and taxonomy of anodontine species in Lake Baikal and Transbaikalia region has been contentious since it is based on a typological species concept, the so called “Comparatory Method”. Using this method, six Comparatory anodontine species have been described for the study area as belonging to the genus <i>Colletopterum</i>. This genus was separated from <i>Anodonta</i> based on shell characteristics and further split into two subgenera, i.e. <i>Colletopterum</i> sensu stricto and <i>Colletopterum</i> (<i>Piscinaliana)</i>. However, many authors do not recognize this separation maintaining all <i>Colletopterum</i> forms within <i>Anodonta</i>. The current study clarifies the taxonomy and systematics of Anodontinae in this region, using a combination of molecular, morphological and anatomical data. All previously recognized Comparatory forms are here recognized as a single species, i.e. <i>Anodonta anatina</i>.</p></div

Unravelling the systematics of <i>Nodularia</i> (Bivalvia, Unionidae) species from eastern Russia

<p>Conservation efforts have been hindered by data deficient conservation status assessments, especially due to taxonomic problems. This is especially true for many eastern Russian species of freshwater mussels, where distinct classification systems have complicated their delimitation and identification. <i>Nodularia</i> is a widespread eastern Asian freshwater mussel genus, present from Vietnam in the south to the Magadan region in eastern Russia in the north. The number of recognized species in the genus <i>Nodularia</i> in eastern Russia has been inflated over the last several decades due to the use of a typological species concept, the so-called 'Comparatory Method'. This method uses a single diagnostic character for species delimitation, i.e., the arc of maximal convexity of the shell's outline. Using this classification system, 10 species were recognized for far eastern Russia under the genus <i>Nodularia</i> Conrad, 1853, divided into three subgenera: <i>Nodularia</i> s. str., <i>Amurunio</i> and <i>Magadaninaia</i>. Since it is not supported by any other classification methods, the current comparatory classification is rejected by many Russian and international scientists, who only recognize a single species for that region, i.e., <i>Nodularia douglasiae</i>. Therefore, the aim of the present study is to clarify the taxonomy and systematics of the <i>Nodularia</i> genus in far eastern Russia and adjacent territories, using a multiple dataset approach that combines distribution with detailed conchological and anatomical analyses with morphometry and COI barcoding molecular techniques. All analyses performed in this study support the existence of a single <i>Nodularia</i> species in eastern Russia, i.e., <i>N. douglasiae</i>.</p

Umbo sculpture in <i>Colletopterum</i> species from studied region of Lake Baikal and Transbaikalia.

<p>Umbo sculpture in <i>Colletopterum</i> species from studied region of Lake Baikal and Transbaikalia.</p

TCS-CM species distribution of collected specimens.

<p>Presence +, Absence -.</p

List of all individual specimens used for genetic analyses, collection sites and GenBank accession codes.

<p>List of all individual specimens used for genetic analyses, collection sites and GenBank accession codes.</p

Change of shell shape and shell convexity with growth of shell length and index B/H in different age groups of TCS-CM <i>Colletopterum</i> species from different localities.

<p><b>B</b>–Lake Baikal, <b>T</b>–Transbaikalia, <b>ER</b>–European Russia: <b>1</b> –young and group of <i>C</i>. <i>sorensianum</i> including <i>C</i>. <i>subcirculare</i> and <i>C</i>. <i>baeri</i>, <b>2</b> –group of <i>C</i>. <i>nilssonii</i> including <i>C</i>. <i>ostiarium</i> and <i>C</i>. <i>milaschevichi</i>, <b>3 –</b>group of <i>C</i>. <i>piscinale</i> including <i>C</i>. <i>convexum</i>, <b>4 –</b>group of <i>C</i>. <i>anatinum</i> with transitional form <i>C</i>. <i>apollonicum</i>, <b>5</b> –group of <i>C</i>. <i>ponderosum</i> and <b>6</b> –group of <i>С</i>. <i>rostratum</i>.</p