Paleoenvironmental changes in marginal seas on the coast of the northwestern Pacific during the Quaternary have caused genetic differentiation and subsequent secondary contacts between populations of coastal organisms in this region. However, little is known about how geographical isolation and the subsequent connection events associated with these multiple marginal seas have shaped the population structure of coastal organisms in the boundary area. The coastal area of Kyushu Island of the Japanese Archipelago, where the East China Sea (ECS), the Sea of Japan (SJ), and the Pacific Ocean (PO) adjoin within a narrow region, would be a suitable field for elucidating the effect of multiple vicariances. Herein, we conducted phylogeographical analyses of the intertidal goby Chaenogobius annularis, focusing on populations around Kyushu Island, using partial mitochondrial (mt) DNA sequences and analysis of 8 microsatellite (ms) DNA loci. We discovered a new lineage distributed along the coast of the ECS distinct from the already-known SJ and PO lineages, which we termed the ECS lineage. This ECS lineage showed remarkable mito-nuclear discordance: mtDNA analyses indicated that the ECS lineage is a highly diverged lineage branched from the PO lineage, whereas msDNA analyses suggested that the ECS lineage is closely related to the SJ lineage. This discordance could have been due to ancient hybridization. In addition, we detected SJ-PO and ECS-SJ hybrid zones on the western Seto Inland Sea and on the northwestern coast of Kyushu, respectively. Such a complex population structure suggests that the secondary contacts after multiple isolation events among marginal seas around Kyushu have a great impact on coastal biodiversity in the area and emphasize the peculiarities of the region.

中文翻译：

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九州岛周围潮间带虾虎鱼的复杂系统地理学模式作为三个不同海洋的边界带

第四纪西北太平洋沿岸边缘海的古环境变化导致了该地区沿海生物种群之间的遗传分化和随后的二次接触。然而，人们对地理隔离以及与这些多个边缘海相关的后续连接事件如何塑造边界区域沿海生物的种群结构知之甚少。东海（ECS）、日本海（SJ）和太平洋（PO）在狭小的区域内毗邻的日本列岛九州岛沿海地区将是阐明影响的合适领域的多个替代品。在此，我们对潮间带虾虎鱼 Chaenogobius ringis 进行了系统地理学分析，重点研究了九州岛周围的种群，使用部分线粒体 (mt) DNA 序列并分析 8 个微卫星 (ms) DNA 位点。我们发现了一个沿 ECS 海岸分布的新谱系，不同于已知的 SJ 和 PO 谱系，我们将其称为 ECS 谱系。该 ECS 谱系显示出显着的线粒体核不一致：mtDNA 分析表明 ECS 谱系是从 PO 谱系分支的高度分化的谱系，而 msDNA 分析表明 ECS 谱系与 SJ 谱系密切相关。这种不一致可能是由于古代杂交造成的。此外，我们分别在濑户内海西部和九州西北海岸发现了 SJ-PO 和 ECS-SJ 混合区。