The revenant: rediscovery of <i>Margaritifera homsensis</i> from Orontes drainage with remarks on its taxonomic status and conservation (Bivalvia: Margaritiferidae)

<p>Since <i>Margaritifera marocana</i> (Pallary, 1918) and <i>M. laosensis</i> (Lea, 1863) were rediscovered, <i>M. homsensis</i> (Lea, 1865) remains the only pearl mussel species known solely based on old shell samples from natural history museums. This is also the last pearl mussel species, which is absent in a phylogeny of the family. Here, we aimed to provide an integrative revision of the taxonomic status of <i>M. homsensis</i> from the Orontes Basin. Using a newly collected specimen from the River Karasu, Hatay Province, southern Turkey, five gene partitions were sequenced, the cytochrome c oxidase subunit I (COI), large ribosomal subunit rRNA (16S), large ribosomal subunit rDNA (28S) and its D3 expansion segment (D3), and small ribosomal subunit rDNA (18S). The multi-gene phylogeny indicates that <i>M. homsensis</i> is a sister taxon of <i>M. auricularia</i>, but both these species are closely related to <i>M. marocana</i> by nuclear genes. The main conchological features, i.e<i>.</i>, the shell shape, teeth morphology, and mantle attachment scars, as well as Fourier shell shape analysis have not shown principal differences between <i>M. homsensis</i> and <i>M. auricularia</i>. Based on these data, we concluded that <i>M. homsensis</i> is a valid species that is most closely related to <i>M. auricularia</i>. Special conservation efforts for a population of <i>M. homsensis</i> discovered in Turkey, including the formation of a nature reserve, might contribute to the conservation of the species. Finally, an extensive search for surviving populations in Orontes drainage (southern Turkey, Lebanon, and Syria) and the Nahr-el-Kabir River (Lebanon and Syria) remains necessary to develop a transboundary conservation strategy for this unique taxon.</p

Range map of <i>Margaritifera dahurica</i> (Middendorff, 1850).

<p>Green circles are representing recent viable populations (observed since 2000), white circles—old records (until 2000). Question mark is indicated an uncertain record from the Langry River [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref069" target="_blank">69</a>], [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref026" target="_blank">26</a>]. Grey areas are indicated an approximate modern species range (it is shown only for the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s002" target="_blank">S2 Table</a>.</p

Map of location of the field study areas.

<p>1—Kamchatka Peninsula (2012, I. Bolotov, Y. Bespalaya, I. Vikhrev, M. Gofarov), 2—Central Sakhalin (2012, same team), 3—southern Sakhalin (2011–2012, same team & Y. Kolosova, O. Aksenova), 4—Kunashir Island (2011, same team & Y. Kolosova, O. Aksenova), 5—Primorye (2012, same team), 6—Transbaikalia (2004–2011, O.K. Klishko). Data on the studied river sites are presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s001" target="_blank">S1</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s004" target="_blank">S4</a> Tables.</p

Shells of <i>Margaritifera togakushiensis</i> (Kondo and Kobayashi, 2005) and <i>Margaritifera middendorffi</i> (Rosén, 1926).

<p>A—Holotype of <i>M</i>. <i>togakushiensis</i> [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.ref018" target="_blank">18</a>]: 137, figs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.g005" target="_blank">5</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.g008" target="_blank">8</a>. B—Lectotype of <i>M</i>. <i>middendorffi</i> (ZISP: no. 6). Photo by I. V. Vikhrev. Scale bar—2 cm.</p

Range map of <i>Margaritifera middendorffi</i> (Rosén, 1926) and <i>Margaritifera togakushiensis</i> (Kondo and Kobayashi, 2005).

<p>Circles—<i>M</i>. <i>middendorffi</i> locations, squares—<i>M</i>. <i>togakushiensis</i> locations. Green circles and squares are representing recent viable populations (observed since 2000), white circles—old records (until 2001), yellow squares—records without exact dates. Grey areas indicate approximate modern species ranges (showing only the large river systems). Species locality numbers on the map correspond to numbers in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s003" target="_blank">S3 Table</a>.</p

Shells of <i>Margaritifera dahurica</i> (Middendorff, 1850).

<p>A—Lectotype (ZISP: no. 7a). B—specimen from Komarovka River, Razdolnaya River basin, Primorye. Photos by I.V. Vikhrev. Scale bar—2 cm.</p

General plan of soft tissue of three Far Eastern margaritiferid species.

<p>A—<i>Margaritifera dahurica</i> (Middendorff, 1850). B—<i>M</i>. <i>laevis</i> (Haas, 1910). C—<i>M</i>. <i>middendorffi</i> (Rosén, 1926). Scale bar—1 cm.</p

Typical habitats of the Eastern Asian margaritiferid species.

<p>A—<i>Margaritifera dahurica</i> (Middendorff, 1850): the Ilystaya River, Primorsky Kray. B—<i>M</i>. <i>middendorffi</i> (Rosén, 1926): the Nachilova River, Kamchatka. C—<i>M</i>. <i>middendorffi</i> (Rosén, 1926) & <i>M</i>. <i>laevis</i> (Haas, 1910): the Golovnina River, Kunashir Island. Photos by Y.V. Bespalaya, Y.S. Kolosova & I.V. Vikhrev.</p

Shells of <i>Margaritifera laevis</i> (Haas, 1910).

<p>A—Sennaya River, Kunashir Island. B—Tym’ River, Sakhalin Island. Photos by I. V. Vikhrev. Scale bar—2 cm.</p

Bayesian phylogeny of <i>Margaritifera</i> spp. haplotypes.

<p>The scale bar indicates the branch length. Asterisks: Posterior probabilities ≥0.95; other significant support node values are mentioned in the figure. For detailed locality and specimen data for analyzed haplotypes, see the supplementary materials (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s001" target="_blank">S1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0122408#pone.0122408.s002" target="_blank">S2</a> Tables). A—The 18S rDNA gene dataset. B—The COI gene dataset.</p