The Eocene–Oligocene sea‐level fall has been viewed as a primary driver of biological succession. We used Anisogammaridae living in both marine and freshwater habitats to test the hypothesis that Eocene–Oligocene sea‐level fall can explain the marine–freshwater habitat shift in the Far East. We obtained three mitochondrial and two nuclear fragments for 138 samples representing 31 species, covering marine and freshwater habitats from latitudes 24 to 50°N. The phylogenetic analyses revealed that freshwater Anisogammaridae is monophyletic. Divergence‐time estimation and ancestral range reconstruction indicate that the family originated from a marine habitat in the North Pacific region during the Eocene and separated between marine and freshwater lineages at 38 Ma. The freshwater lineage diversified at 27 Ma, and further diverged into lotic and lentic clades. Our results suggest that the Eocene–Oligocene sea‐level fall provided an opportunity for marine‐derived Anisogammaridae to shift to new freshwater habitats. The freshwater anisogammarids dispersed from north to south, resulting in the restriction of current marine species restricted to the latitudes 35–50°N and the range of freshwater species in latitudes 24–40°N. Deep divergences within the freshwater lineage were related to the separation of lotic and lentic environments and the opening of the Japan Sea.

中文翻译：

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始新世-渐新世海平面下降推动远东片脚类动物栖息地从海洋向淡水转移

始新世-渐新世海平面下降被视为生物演替的主要驱动因素。我们使用生活在海洋和淡水栖息地的 Anisogammaridae 来检验始新世 - 渐新世海平面下降可以解释远东海洋 - 淡水栖息地变化的假设。我们获得了代表 31 个物种的 138 个样本的三个线粒体和两个核碎片，覆盖了北纬 24 度到 50 度的海洋和淡水栖息地。系统发育分析表明，淡水 Anisogammaridae 是单系的。发散时间估计和祖先范围重建表明，该家族起源于始新世期间北太平洋地区的海洋栖息地，并在 38 Ma 时在海洋和淡水谱系之间分离。淡水谱系在 27 Ma 多样化，并进一步分化为 Lotic 和 lentic 进化枝。我们的研究结果表明，始新世-渐新世海平面下降为海洋衍生的 Anisogammaridae 转移到新的淡水栖息地提供了机会。淡水异鱼科动物自北向南分散，导致目前海洋物种限制在北纬35-50°，淡水物种分布在北纬24-40°。淡水谱系内的深层分歧与流水和弱水环境的分离以及日本海的开放有关。导致目前海洋物种被限制在北纬 35-50°和淡水物种范围在北纬 24-40°。淡水谱系内的深层分歧与流水和弱水环境的分离以及日本海的开放有关。导致目前海洋物种被限制在北纬 35-50°和淡水物种范围在北纬 24-40°。淡水谱系内的深层分歧与流水和弱水环境的分离以及日本海的开放有关。