Data from: Artificial barriers prevent genetic recovery of small isolated populations of a low-mobility freshwater fish

Habitat loss and fragmentation often result in small, isolated populations vulnerable to environmental disturbance and loss of genetic diversity. Low genetic diversity can increase extinction risk of small populations by elevating inbreeding and inbreeding depression, and reducing adaptive potential. Due to their linear nature and extensive use by humans, freshwater ecosystems are especially vulnerable to habitat loss and fragmentation. Although the effects of fragmentation on genetic structure have been extensively studied in migratory fish, they are less understood in low-mobility species. We estimated impacts of instream barriers on genetic structure and diversity of the low-mobility river blackfish (Gadopsis marmoratus) within five streams separated by weirs or dams constructed 45–120 years ago. We found evidence of small-scale (<13 km) genetic structure within reaches unimpeded by barriers, as expected for a fish with low mobility. Genetic diversity was lower above barriers in small streams only, regardless of barrier age. In particular, one isolated population showed evidence of a recent bottleneck and inbreeding. Differentiation above and below the barrier was greatest (FST =0.13) in this stream, but in other streams did not differ from background levels. Spatially explicit simulations suggest that short-term barrier effects would not be detected with our dataset unless effective population sizes were very small (<100). Our study highlights that, in structured populations, the ability to detect short-term genetic effects from barriers is reduced and requires more genetic markers compared to panmictic populations. We also demonstrate the importance of accounting for natural population genetic structure in fragmentation studies.生境丧失与片段化往往会导致种群规模缩小并呈现隔离状态，这类种群极易受到环境扰动的影响，同时面临遗传多样性丧失的风险。遗传多样性水平低下会通过提升近交程度、加剧近交衰退以及降低适应潜力，进一步增加小型种群的灭绝风险。淡水生态系统因其线性分布特征与人类的广泛开发利用，尤其容易受到生境丧失与片段化的冲击。尽管学界已针对洄游鱼类的片段化效应与遗传结构的关联开展了大量研究，但对低移动性物种的相关机制仍缺乏充分认知。本研究以5条分别于45至120年前修建有堰坝或水坝的溪流为研究对象，评估了溪流内障碍物对低移动性物种河黑鲈（Gadopsis marmoratus）的遗传结构与遗传多样性的影响。研究发现，在无障碍物阻隔的河段内存在小规模（<13千米）的遗传结构，这与低移动性鱼类的预期特征相符。仅在小型溪流的障碍物上游区域，遗传多样性水平显著更低，且该现象与障碍物的修建年限无关。尤为值得注意的是，其中一个隔离种群展现出近期种群瓶颈与近交的相关证据。该溪流中障碍物上下游的遗传分化程度最高（FST=0.13），而其余溪流的遗传分化水平则与背景基准值无显著差异。空间显式模拟结果显示，除非有效种群规模极小（<100），否则本研究数据集无法检测到障碍物的短期遗传效应。本研究表明，相较于随机交配种群，在具有自然遗传结构的种群中，检测障碍物引发的短期遗传效应的能力会下降，且需要更多的遗传标记。本研究同时证实，在生境片段化相关研究中，充分考虑种群自然遗传结构的重要性。