The morphologically similar populations of the Korean freshwater spined loach recently described as a new species Cobitis nalbanti (Actinopterygii: Cypriniformes: Cobitidae) inhabit the rivers and streams on the Korean Peninsula that flow into the Yellow Sea and the Korea Strait. These shallow sea areas have experienced recurrent sea-level rises and falls. In this study, we investigate the impact of repeated disconnection and reconnection of rivers on the population genetics and morphological variation of C. nalbanti. A total of 264 individuals of C. nalbanti were collected from 17 localities covering the entire distribution range of this species in South Korea. We examined multi-locus genetic data including a mitochondrial gene, seven nuclear genes and eight microsatellite loci, and scrutinized 31 morphological variables based on 26 morphometric and 3 meristic characters. We uncovered a population genetic structure and noticeable morphological variation among populations approximately corresponding to the geography of river basins along the Yellow Sea. Overall genetic diversity was significantly reduced in the more northern populations, suggesting range expansion from ancestral southern populations into northern rivers via the paleo-Yellow River system in the Yellow Sea during glacial periods of lowered sea levels. A northward range expansion hypothesis was strongly supported by the reconstruction of geographic ranges of ancestral species and/or populations based on phylogenetic analyses. Both mitochondrial and nuclear phylogenetic trees revealed a relatively highly divergent lineage of C. nalbanti in the southernmost populations (Tamjin lineage). Noticeable differences in morphological variables between the Tamjin lineage and other lineages of C. nalbanti also suggest potential separate specific status of the former. The close phylogenetic relationships between the Tamjin lineage and the Japanese species of Cobitis signify interaction or exchange between the Korean and Japanese cobitids and imply that there was historically at least one freshwater passage on the terrestrial bridge between the Korean Peninsula and the southwestern part of the Japanese archipelago.

中文翻译：

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遗传模式揭示了 Nalbant 刺泥鳅 Cobitis nalbanti sensu lato（Teleostei：Cypriniformes：Cobitidae）的向北范围扩张和神秘多样性

形态相似的韩国淡水鳅种群最近被描述为新种鳅（Actinopterygii：Cypriniformes：Cobitidae），栖息在朝鲜半岛流入黄海和朝鲜海峡的河流和溪流中。这些浅海区域经历了反复的海平面上升和下降。在这项研究中，我们调查了河流反复断开和重新连接对 C. nalbanti 种群遗传和形态变异的影响。从覆盖该物种在韩国整个分布范围的 17 个地点共收集了 264 只 C. nalbanti 个体。我们检查了多基因座遗传数据，包括一个线粒体基因、七个核基因和八个微卫星基因座，并根据 26 个形态测量和 3 个分生特征仔细检查了 31 个形态变量。我们发现了种群遗传结构和种群间显着的形态变异，大致对应于黄海沿岸流域的地理。在更北部的种群中，总体遗传多样性显着降低，这表明在海平面降低的冰川时期，范围从黄海的古黄河系统从南方祖先种群扩展到北方河流。基于系统发育分析重建祖先物种和/或种群的地理范围，有力地支持了向北范围扩展的假设。线粒体和核系统发育树都揭示了 C. 最南端种群中的 nalbanti（Tamjin 谱系）。Tamjin 谱系和 C. nalbanti 的其他谱系之间形态变量的显着差异也表明前者可能具有单独的特定状态。Tamjin 谱系与日本 Cobitis 物种之间的密切系统发育关系表明朝鲜和日本 cobitids 之间的相互作用或交换，并暗示历史上朝鲜半岛和日本西南部之间的陆桥上至少有一条淡水通道群岛。