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

TCS-CM species distribution of collected specimens.

<p>Presence +, Absence -.</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

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

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

Inner anatomy features in <i>Colletopterum</i> specimens from Lake Baikal and Transbaikalia.

<p>General view of soft body <b>4.1 –</b>male, <b>4.2–4.3</b> –female with mature glochidia: <b>m</b>–mantle, <b>ig</b>–inner gills, <b>og</b>–outer gills, <b>lp</b>–labial palps, <b>f</b>–foot, <b>ia</b>–inner aperture, <b>ea</b>–excurrent aperture, <b>sa</b>–supra-anal aperture, <b>aam</b>–anterior adductor muscle, <b>pam</b>–posterior adductor muscle; <b>4.4</b>: <b>pia1 –</b>retracted position and <b>pia</b>–normal position of papillae in the inner aperture, <b>4.5–4.8</b>: <b>pia</b>–papillae shape of the inner aperture and <b>pg</b>–different pigmentation of excurrent aperture, <b>4.9 –</b>papillae scaled-up.</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

COI haplotype (TCS) network showing the relationships <i>A</i>. <i>anatina</i> haplotypes.

<p>Colour codes correspond to the 5 haplogroups: Blue—Northwest Iberia; Green—Southcentral Iberia; Red Southwest Iberia; Purple—Europe; Yellow—Western Mediterranean. Within the European haplogroup, Russian haplotypes are represented in dark purple and Ukrainian in light purple. Circle size is proportional to the observed haplotype frequencies, white dots represent unobserved haplotypes.</p

Shell metrics and TCS-CM identification of collected specimens.

<p>Shell metrics and TCS-CM identification of collected specimens.</p

Shell measurements used for morphometry and species identification.

<p><b>1 –</b>lateral shell view showing: the distance from umbo apex to anterior shell margin (<b>l</b>) and shell maximal height (<b>Hm</b>) from umbo apex to ventral shell margin across maximal convex point of valves (<b>mcp</b>); <b>2</b> –dorsal shell view showing the <b>mcp</b>; <b>3</b> –anterior shell view and shell width (<b>B</b>) in the maximal convex point (<b>mcp</b>); <b>4</b> –arcs of maximal convexity of the valve outline of Baikalian species (Prozorova & Bogatov, 2006): <b>A</b>–<i>C</i>. <i>ponderosum</i> Pfeiffer 1825, <b>B–</b><i>C</i>. <i>anatinum</i> Linnaeus 1758, <b>C</b>–<i>C</i>. <i>piscinale</i> Nilsson 1822, <b>D</b>–<i>C</i>. <i>nilssonii</i> Küester 1842, <b>E</b>–<i>C</i>. <i>sorensianum</i> Dybowsky, 1913; <b>5</b> –arcs of maximal convexity of the valve outline of Eurasian species: <b>g<i>–</i></b> <i>С</i>. <i>rostratum</i> Rossmaessler 1836, <b>h<i>–</i></b><i>C</i>. <i>ponderosum</i>, <b>i<i>–</i></b><i>C</i>. <i>anatinum</i>, <b>j<i>–</i></b> <i>С</i>. <i>piscinale</i>, <b>k<i>–</i></b><i>C</i>. <i>nilssonii</i>, <b>l<i>–</i></b><i>C</i>. <i>sorensianum</i>, and <b>6 –</b>of European species: <b>a</b>–<i>C</i>. <i>apollonicum</i> (Bourguignat 1880), <b>b</b>–<i>C</i>. <i>convexum</i> (Drouet 1888), <b>c</b>–<i>C</i>. <i>milaschevichi</i> Bogatov, Starobogatov et Prozorova 2005, <b>d</b>–<i>C</i>. <i>ostiarium</i> (Drouet 1881), <b>e</b>–<i>C</i>. <i>baeri</i> Bogatov, Starobogatov et Prozorova 2005, <b>f–</b><i>C</i>. <i>subcirculare</i> (Clessin 1873) according to Bogatov et al. (2005).</p