Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi 980-8577, Japan.
Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotlářská 2, Brno 611 37, Czech Republic; Center for Northeast Asian Studies, Tohoku University, 41 Kawauchi, Aoba, Sendai, Miyagi 980-8576, Japan.
Mol Phylogenet Evol. 2022 Oct;175:107563. doi: 10.1016/j.ympev.2022.107563. Epub 2022 Jul 6.
Accurate species identification is of primary importance in ecology and evolutionary biology. For a long time, the unionid mussels Beringiana and Sinanodonta have puzzled researchers trying to unravel their diversity because of their poorly discernible morphologies. A recent study conducted species delineation of unionid mussels based on mitochondrial DNA variation, opening up a new avenue to grasp species diversity of the mussels. However, mtDNA-based classification may not align with species boundaries because mtDNA is prone to introgression and incomplete lineage sorting that cause discordance between species affiliation and gene phylogeny. In this study, we evaluated the validity of the mtDNA-based classification of unionid mussels Beringiana and Sinanodonta in Japan using mitochondrial sequence data, double digest restriction site-associated DNA library (ddRAD) sequencing, and morphological data. We found significant inconsistencies in the mitochondrial and nuclear DNA phylogenies, casting doubt on the reliability of the mtDNA-based classification in this group. In addition, nuclear DNA phylogeny revealed that there are at least two unionid lineages hidden in the mtDNA phylogeny. Although molecular dating technique indicates that Beringiana and Sinanodonta diverged >35 million years ago, their shell morphologies are often indistinguishable. Specifically, morphological analyses exhibited the parallel appearance of nearly identical ball-like shell forms in the two genera in Lake Biwa, which further complicates species identification and the morphological evolution of unionid mussels. Our study adds to a growing body of literature that accurate species identification of unionid mussels is difficult when using morphological characters alone. Although mtDNA-based classification is a simple and convenient way to classify unionid mussels, considerable caution is warranted for its application in ecological and evolutionary studies.
准确的物种鉴定在生态学和进化生物学中至关重要。长期以来，贻贝属的伯灵氏贝和无齿蚌由于其形态难以区分，一直困扰着试图揭示其多样性的研究人员。最近的一项研究基于线粒体 DNA 变异对贻贝进行了物种划分，为掌握贻贝的物种多样性开辟了新途径。然而，基于 mtDNA 的分类方法可能与物种界限不一致，因为 mtDNA 容易发生基因渗入和不完全谱系分选，导致物种归属和基因系统发育之间出现不匹配。在本研究中，我们使用线粒体序列数据、双酶切限制位点相关 DNA 文库（ddRAD）测序和形态数据，评估了日本贻贝属伯灵氏贝和无齿蚌的 mtDNA 分类有效性。我们发现线粒体和核 DNA 系统发育之间存在显著不一致，这对该类群基于 mtDNA 的分类的可靠性提出了质疑。此外，核 DNA 系统发育揭示，在 mtDNA 系统发育中至少隐藏着两个贻贝谱系。尽管分子定年技术表明伯灵氏贝和无齿蚌在 3500 多万年前就已经分化，但它们的贝壳形态往往难以区分。具体来说，形态分析显示在琵琶湖的两个属中出现了几乎相同的球状贝壳形态，这进一步增加了物种鉴定的难度和贻贝的形态进化的复杂性。本研究增加了越来越多的文献，表明仅使用形态特征对贻贝进行准确的物种鉴定是困难的。虽然基于 mtDNA 的分类是一种简单方便的贻贝分类方法，但在生态和进化研究中应用时需要相当谨慎。
