Human-induced habitat fragmentation effects on connectivity, diversity and population persistence of an endemic fish, Percilia irwini, in the Biobío river basin (Chile)

An understanding of how genetic variability is distributed in
space is fundamental for the conservation and maintenance of diversity in
spatially fragmented and vulnerable populations. While fragmentation can
occur from natural barriers it can also be exacerbated by anthropogenic
activities such as hydroelectric power plant development. Whatever the
source, fragmentation can have significant ecological effects, including
the disruptions of migratory processes and gene flow among populations. In
Chile, the Biobío river basin exhibits a high degree of habitat
fragmentation due to the numerous hydroelectric power plants in operation,
the number of which is expected to increase following new renewable energy
use strategies. Here, we assessed the effects of different kinds of
barriers on the genetic structure of the endemic freshwater fish Percilia
irwini, knowledge that is critically needed to inform conservation
strategies in light of current and anticipated further fragmentation
initiatives in the system. We identified 8 genetic units throughout the
entire Biobío system with high effective sizes. A reduced effective size
estimate was however observed in a single population located between two
impassable barriers. Both natural waterfalls and human made dams were
important drivers of population differentiation in this system, however,
dams affect genetic diversity differentially depending on their mode of
operation. Evidence of population extirpation was found in two river
stretches limited by upstream and downstream dams. Significant gene flow
in both directions was found among populations not separated by natural or
anthropogenic barriers. Our results suggest a significant vulnerability of
P. irwini populations to future dam development and demonstrate the
importance of studying basin-wide data sets with genetic metrics to
understand the strength and direction of anthropogenic impacts on fish
populations.

明晰遗传变异在空间尺度上的分布格局，是保护和维持空间破碎化脆弱种群多样性的核心前提。栖息地破碎化既可由天然屏障引发，也会因水电开发等人为活动进一步加剧。无论成因如何，破碎化均会产生显著生态效应，包括破坏种群间的洄游过程与基因流。智利比奥比奥河流域因境内运营的多座水力发电厂，已呈现高度的栖息地破碎化特征，且随着新可再生能源利用策略的推进，电站数量预计还将进一步增加。
本研究评估了不同类型屏障对特有淡水鱼种Percilia irwini遗传结构的影响——这一研究结果对于结合当前及流域未来的破碎化开发计划制定保护策略而言，具有至关重要的指导意义。我们在整个比奥比奥河流域中共鉴定出8个遗传单元，且各单元均具有较高的有效种群大小。但在一处夹在两道不可通行屏障之间的种群中，观测到有效种群大小显著降低。天然瀑布与人工大坝均为该流域内种群分化的重要驱动因子，但大坝对遗传多样性的影响取决于其运行模式。在受上下游大坝阻隔的两段河道中，发现了种群局部灭绝的证据。未受天然或人为屏障阻隔的种群间，存在双向显著的基因流。
本研究结果表明，Percilia irwini种群对未来大坝开发存在显著脆弱性，同时证实了利用遗传指标开展全流域数据集研究，对于明晰人为活动对鱼类种群影响的强度与方向具有重要价值。