Understanding the effect of human-induced landscape fragmentation on gene flow and evolutionary potential of wild populations has become a major concern. Here, we investigated the effect of riverscape fragmentation on patterns of genetic diversity in the freshwater resident European brook lamprey (Lampetra planeri) that has a low ability to pass obstacles to migration. We tested the hypotheses of (i) asymmetric gene flow following water current and (ii) an effect of gene flow with the closely related anadromous river lamprey (L. fluviatilis) ecotype on L. planeri genetic diversity. We genotyped 2472 individuals, including 225 L. fluviatilis, sampled from 81 sites upstream and downstream barriers to migration, in 29 western European rivers. Linear modelling revealed a strong positive relationship between genetic diversity and the distance from the river source, consistent with expected patterns of decreased gene flow into upstream populations. However, the presence of anthropogenic barriers had a moderate effect on spatial genetic structure. Accordingly, we found evidence for downstream-directed gene flow, supporting the hypothesis that barriers do not limit dispersal mediated by water flow. Downstream L. planeri populations in sympatry with L. fluviatilis displayed consistently higher genetic diversity. We conclude that genetic drift and slight downstream gene flow drive the genetic make-up of upstream L. planeri populations whereas gene flow between ecotypes maintains higher levels of genetic diversity in L. planeri populations sympatric with L. fluviatilis. We discuss the implications of these results for the design of conservation strategies of lamprey, and other freshwater organisms with several ecotypes, in fragmented dendritic river networks.

中文翻译：

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溪七鳃鳗的河流景观遗传学：河流破碎化对遗传多样性的影响小于溯河产卵生态型基因流的影响


了解人类引起的景观破碎化对野生种群基因流和进化潜力的影响已成为一个主要问题。在这里，我们研究了河流景观破碎化对淡水栖息的欧洲七鳃鳗（Lampetra planeri）遗传多样性模式的影响，这种七鳃鳗穿过迁徙障碍的能力较低。我们测试了以下假设：（i）水流后的不对称基因流和（ii）与密切相关的溯河产卵河七鳃鳗（L.fluviatilis）生态型的基因流对 L. planeri 遗传多样性的影响。我们对 2472 个个体（包括 225 个河乳杆菌）进行了基因分型，这些个体是从 29 条西欧河流的迁徙障碍上游和下游的 81 个地点采样的。线性模型揭示了遗传多样性与距河流源头的距离之间存在很强的正相关关系，这与流入上游种群的基因流减少的预期模式一致。然而，人为障碍的存在对空间遗传结构有中等影响。因此，我们发现了基因向下游流动的证据，支持了障碍不会限制水流介导的扩散的假设。与 L.fluviatilis 相似的下游 L. planeri 种群表现出一贯较高的遗传多样性。我们得出的结论是，遗传漂变和轻微的下游基因流驱动了上游 L. planeri 种群的遗传组成，而生态型之间的基因流则在与 L. Fluviatilis 同域的 L. planeri 种群中维持了较高水平的遗传多样性。我们讨论了这些结果对七鳃鳗和其他具有多种生态类型的淡水生物在支离破碎的树突河网络中的保护策略设计的影响。