Impacts of urban development on aquatic populations are often complex and difficult to ascertain, but population genetic analysis has allowed researchers to monitor and estimate gene flow in context of existing and future hydroelectric projects. The Lower Mekong Basin is undergoing rapid hydroelectric development with around 50 completed and under construction dams and 95 planned dams. We investigated the baseline genetic diversity of two exploited migratory fishes, the Mud Carp Henicorhynchus lobatus (five locations) and the Rat-faced Pangasiid Helicophagus leptorhynchus (two locations), in the Lower Mekong Basin using the genomic ddRAD method. In both species, fish sampled upstream of Khone Falls are differentiated from those collected at other sites, and Ne estimates at the site above the falls are lower than at other sites. This was the first study to utilize thousands of RAD-generated SNPs to indicate that the Mekong's Khone Falls are a potential barrier to gene flow for these two moderately migratory species. The recent completion of the Don Sahong dam across one of the only channels for migratory fishes through Khone Falls may further exacerbate signatures of isolation and continue to disrupt the migration patterns of regionally vital food fishes. Additionally, Hen. lobatus populations downstream of Khone Falls, including the 3S basin and Tonle Sap system, displayed robust connectivity. Potential obstruction of migration pathways between these river systems resulting from future dam construction may limit dispersal, which has led to elevated inbreeding rates and even local extirpation in other fragmented riverine species.

中文翻译：

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跨越天然河流屏障的两条湄公河鱼类种群遗传结构的证据

城市发展对水生种群的影响通常很复杂且难以确定，但种群遗传分析使研究人员能够在现有和未来水电项目的背景下监测和估计基因流。湄公河下游盆地正在快速发展水力发电，大约有 50 座已建成和在建的大坝和 95 座计划中的大坝。我们使用基因组 ddRAD 方法调查了湄公河下游流域中两种被开发的洄游鱼类，即鲢鱼 Henicorhynchus lobatus（五个地点）和鼠脸 Pangasiid Helicophagus leptorhynchus（两个地点）的基线遗传多样性。在这两个物种中，在孔瀑布上游取样的鱼与在其他地点采集的鱼不同，瀑布上方地点的 Ne 估计值低于其他地点。这是第一项利用数以千计 RAD 生成的 SNP 来表明湄公河的孔瀑布是这两种适度洄游物种基因流动的潜在障碍的研究。最近建成的 Don Sahong 大坝是通过孔瀑布的唯一洄游鱼类通道之一，这可能会进一步加剧孤立现象，并继续破坏区域重要食用鱼类的洄游模式。此外，母鸡。孔瀑布下游的 lobatus 种群，包括 3S 盆地和洞里萨湖系统，显示出强大的连通性。未来大坝建设可能会阻碍这些河流系统之间的迁移路径，这可能会限制传播，从而导致近亲繁殖率升高，甚至其他支离破碎的河流物种的局部灭绝。