Unit of Evolutionary Biology and Systematic Zoology, Department of Biochemistry and Biology, University of Potsdam, Potsdam, Germany.
Mol Phylogenet Evol. 2013 Dec;69(3):1063-76. doi: 10.1016/j.ympev.2013.05.021. Epub 2013 Jun 10.
The geological history of the Ponto-Caspian region, with alternating cycles of isolation and reconnection among the three main basins (Black and Azov Seas, and the more distant Caspian Sea) as well as between them and the Mediterranean Sea, profoundly affected the diversification of its aquatic fauna, leading to a high degree of endemism. Two alternative hypotheses on the origin of this amazing biodiversity have been proposed, corresponding to phases of allopatric separation of aquatic fauna among sea basins: a Late Miocene origin (10-6 MYA) vs. a more recent Pleistocene ancestry (<2 MYA). Both hypotheses support a vicariant origin of (1) Black+Azov Sea lineages on the one hand, and (2) Caspian Sea lineages on the other. Here, we present a study on the Ponto-Caspian endemic amphipod Pontogammarus maeoticus. We assessed patterns of divergence based on (a) two mitochondrial and one nuclear gene, and (b) a morphometric analysis of 23 morphological traits in 16 populations from South and West Caspian Sea, South Azov Sea and North-West Black Sea. Genetic data indicate a long and independent evolutionary history, dating back from the late Miocene to early Pleistocene (6.6-1.6 MYA), for an unexpected, major split between (i) a Black Sea clade and (ii) a well-supported clade grouping individuals from the Caspian and Azov Seas. Absence of shared haplotypes argues against either recent or human-mediated exchanges between Caspian and Azov Seas. A mismatch distribution analysis supports more stable population demography in the Caspian than in the Black Sea populations. Morphological divergence largely followed patterns of genetic divergence: our analyses grouped samples according to the basin of origin and corroborated the close phylogenetic affinity between Caspian and Azov Sea lineages. Altogether, our results highlight the necessity of careful (group-specific) evaluation of evolutionary trajectories in marine taxa that should certainly not be inferred from the current geographical proximity of sea basins alone.
本地区域的地质历史，加上三个主要盆地（黑海和亚速海，以及更远的里海）之间以及它们与地中海之间的隔离和再连接的交替循环，深刻地影响了其水生动物群的多样化，导致了高度的特有性。关于这种惊人的生物多样性的起源，已经提出了两种替代假说，这两种假说对应于水生动物群在海盆之间的地理隔离的不同阶段：一种是中新世起源（10-6 百万年前），另一种是更新世起源（<2 百万年前）。这两种假说都支持（1）黑海+亚速海谱系和（2）里海谱系的趋异起源。在这里，我们介绍了对 Pontogammarus maeoticus 这一 Pontocaspian 特有片脚类动物的研究。我们根据（a）两个线粒体和一个核基因，以及（b）对来自南高加索海、南亚速海和西北黑海的 16 个种群的 23 个形态特征的形态测量分析，评估了分化模式。遗传数据表明，从晚中新世到早更新世（6.6-1.6 百万年前），存在着一个漫长而独立的进化历史，这一历史导致了一个意外的、主要的分裂，即（i）黑海支系和（ii）一个由里海和亚速海个体组成的、得到很好支持的支系。没有共享的单倍型表明，里海和亚速海之间没有近期的或人类介导的交流。不匹配分布分析支持里海的种群比黑海的种群具有更稳定的人口动态。形态分化在很大程度上遵循遗传分化的模式：我们的分析根据起源盆地对样本进行了分组，并证实了里海和亚速海谱系之间密切的系统发育亲缘关系。总的来说，我们的研究结果强调了在海洋分类群中，必须对进化轨迹进行仔细的（特定于群体的）评估，而不能仅仅从当前海盆的地理位置接近程度来推断。
