Coldwater, primary freshwater, fish such as the eight-barbel loach, Lefua nikkonis, are thought to have colonised Hokkaido from the continental Far East via Sakhalin Island during the Late Pleistocene. Lefua populations have been reported on southern Sakhalin, but detailed morphological and population structure analyses have not yet been completed. This information is important for reconstructing the colonisation history of L. nikkonis to Hokkaido. In this study, morphological analysis revealed that L. nikkonis and two continental congeners, Lefua pleskei and Lefua costata, are distinguishable from each other, and Lefua collected from southern Sakhalin is morphologically more similar to L. nikkonis. Random forest analysis, a machine learning classification method, classified all Sakhalin individuals as L. nikkonis. Haplotype analysis of mitochondrial DNA sequences revealed that all but one Sakhalin haplotype are shared with L. nikkonis and none is shared with the two continental congeners, which supports the hypothesis that Sakhalin Lefua are L. nikkonis. However, none of the Sakhalin haplotypes was distributed on northern Hokkaido. This discontinuous distribution of haplotypes across Sakhalin and Hokkaido suggests that the Sakhalin Lefua populations are not native. Some of the Sakhalin haplotypes were found only on Hokkaido’s Ishikari River system or the Tokachi River system, suggesting that they originated from these regions. Because previous field surveys reported wild Lefua only from northwestern Sakhalin, we concluded that native Lefua on southern Sakhalin may have gone extinct after they colonised Hokkaido in the Middle Pleistocene.

中文翻译：

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库页岛南部八须鳅属的形态特征和种群遗传结构

冷水、主要淡水、八须鳅、Lefua nikkonis 等鱼类被认为在晚更新世期间从远东大陆经库页岛殖民北海道。南萨哈林岛已有 Lefua 种群的报道，但详细的形态和种群结构分析尚未完成。这些信息对于重建 L. nikkonis 到北海道的殖民历史很重要。在这项研究中，形态学分析表明，L. nikkonis 和两个大陆同系物 Lefua pleskei 和 Lefua costata 彼此可区分，而从库页岛南部采集的 Lefua 在形态上与 L. nikkonis 更相似。随机森林分析是一种机器学习分类方法，将所有库页岛个体分类为 L. nikkonis。线粒体 DNA 序列的单倍型分析显示，除了一种库页岛单倍型外，其他所有单倍型与 L. nikkonis 共享，而没有与两个大陆同源物共享，这支持了 Sakhalin Lefua 是 L. nikkonis 的假设。然而，没有一个库页岛单倍型分布在北海道北部。这种单倍型在库页岛和北海道的不连续分布表明库页岛 Lefua 种群不是本地人。一些库页岛单倍型仅在北海道的石狩河水系或十胜河水系中发现，表明它们起源于这些地区。由于之前的实地调查仅报告了萨哈林岛西北部的野生 Lefua，因此我们得出结论，萨哈林南部的本地 Lefua 可能在中更新世殖民北海道后灭绝。