Expansion and systematics redefinition of the most threatened freshwater mussel family, the Margaritiferidae

Abstract

Two Unionida (freshwater mussel) families are present in the Northern Hemisphere; the Margaritiferidae, representing the most threatened of unionid families, and the Unionidae, which include several genera of unresolved taxonomic placement. The recent reassignment of the poorly studied Lamprotula rochechouartii from the Unionidae to the Margaritiferidae motivated a new search for other potential species of margaritiferids from members of Gibbosula and Lamprotula. Based on molecular and morphological analyses conducted on newly collected specimens from Vietnam, we here assign Gibbosula crassa to the Margaritiferidae. Additionally, we reanalyzed all diagnostic characteristics of the Margaritiferidae and examined museum specimens of Lamprotula and Gibbosula. As a result, two additional species are also moved to the Margaritiferidae, i.e. Gibbosula confragosa and Gibbosula polysticta. We performed a robust five marker phylogeny with all available margaritiferid species and discuss the taxonomy within the family. The present phylogeny reveals the division of Margaritiferidae into four ancient clades with distinct morphological, biogeographical and ecological characteristics that justify the division of the Margaritiferidae into two subfamilies (Gibbosulinae and Margaritiferinae) and four genera (Gibbosula, Cumberlandia, Margaritifera, and Pseudunio). The systematics of the Margaritiferidae family is re-defined as well as their distribution, potential origin and main biogeographic patterns.

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

“…However, a critical taxonomic revision of all these taxa is urgently needed to clarify their status, prospective phylogenetic placement, and validity. Multiple fossil species recovered from the Pleistocene deposits 98 should be compared with recent representatives of the corresponding genera, as many of these nominal taxa may be synonyms of terminal species or their stem lineages 33,101,102 .…”

An unexpected host for the endangered giant freshwater pearl mussel Margaritifera auricularia (Spengler, 1793) as a conservation tool

“…Lampreys are considered 'living fossils' because they have remained largely unaltered for 360 million years (Gess, Coates, & Rubidge, 2006). Thus, these primitive aquatic vertebrates, like sturgeons, could have been the first hosts of the family Margaritiferidae, which originated in the mid-Jurassic (Araujo, Schneider, Roe, Erpenbeck, & Machordom, 2017;Lopes-Lima, Bolotov, et al, 2018), and possibly of other freshwater mussel families.…”

A Taxonomic Revision of Fossil Freshwater Pearl Mussels (Bivalvia: Unionoida: Margaritiferidae) From Pliocene and Pleistocene Deposits of Southeastern Europe

“…Numerous fossil nominal taxa of freshwater pearl mussels (Bivalvia: Unionoida: Margaritiferidae) were introduced by paleontologists based on the differences in shell shape, size, umbo position, shape of adductor scars, and hinge structure (Bogatchev, 1961;Chepalyga, 1964Chepalyga, , 1965Chepalyga, , 1967Devyatkin et al, 1971). However, recent advances in phylogenetic and phylogenomic modeling (Bolotov et al, 2016;Araujo et al, 2017;Lopes-Lima et al, 2018) indicate that these mussels share slow evolutionary and diversification rates.…”

“…Ecologica Montenegrina 21: 1-16 (2019) This journal is available online at: www.biotaxa.org/em Furthermore, studies of recent taxa reveal that freshwater pearl mussels share high levels of intraspecific morphological variability and that minute morphological differences cannot be used as species-level diagnostic characters (Bolotov et al, 2015;Vikhrev et al, 2017;Lopes-Lima et al, 2018). Almost all recent species have strictly allopatric distribution ranges, with the only exception of Margaritifera middendorffi (Rosén, 1926) and M. laevis (Haas, 1910) having a secondary sympatric zone in the Sakhalin Island, South Kurile Archipelago, and Hokkaido (Bolotov et al, 2015(Bolotov et al, , 2016Lopes-Lima et al, 2018).…”

“…Ecologica Montenegrina 21: 1-16 (2019) This journal is available online at: www.biotaxa.org/em Furthermore, studies of recent taxa reveal that freshwater pearl mussels share high levels of intraspecific morphological variability and that minute morphological differences cannot be used as species-level diagnostic characters (Bolotov et al, 2015;Vikhrev et al, 2017;Lopes-Lima et al, 2018). Almost all recent species have strictly allopatric distribution ranges, with the only exception of Margaritifera middendorffi (Rosén, 1926) and M. laevis (Haas, 1910) having a secondary sympatric zone in the Sakhalin Island, South Kurile Archipelago, and Hokkaido (Bolotov et al, 2015(Bolotov et al, , 2016Lopes-Lima et al, 2018). In contrast, a description of fossil sympatric taxa is a commonly accepted approach in systematic paleontology, when 2-3 or more closely related species are described from a single locality (Chepalyga, 1964;Devyatkin et al, 1971;Delvene et al, 2016) that may lead to overestimation of the actual diversity of fossil taxa because the sympatric occurrence of closely related species is an unusual phenomenon (Lopes-Lima et al, 2018).…”