Data from: Genetic and phenotypic population divergence on a microgeographic scale in brown trout

Salmonid populations of many rivers are rapidly declining. One possible explanation is that habitat fragmentation increases genetic drift and reduces the populations’ potential to adapt to changing environmental conditions. We measured the genetic and eco-morphological diversity of brown trout (Salmo trutta) in a Swiss stream system, using multivariate statistics and Bayesian clustering. We found large genetic and phenotypic variation within only 40 km of stream length. Eighty-eight percent of all pairwise FST comparisons and 50% of the population comparisons in body shape were significant. High success rates of population assignment tests confirmed the distinctiveness of populations in both genotype and phenotype. Spatial analysis revealed that divergence increased with waterway distance, the number of weirs, and stretches of poor habitat between sampling locations, but effects of isolation-by-distance and habitat fragmentation could not be fully disentangled. Stocking intensity varied between streams but did not appear to erode genetic diversity within populations. A lack of association between phenotypic and genetic divergence points to a role of local adaptation or phenotypically plastic responses to habitat heterogeneity. Indeed, body shape could be largely explained by topographic stream slope, and variation in overall phenotype matched the flow regimes of the respective habitats.

诸多河流中的鲑科鱼类种群正快速衰退。其中一种可能的解释是，生境破碎化加剧了遗传漂变，降低了种群适应环境变化的潜力。本研究针对瑞士某溪流系统中的褐鳟（Salmo trutta）开展研究，采用多元统计分析与贝叶斯聚类方法，测定了其遗传与生态形态多样性。仅在40公里的溪流范围内，我们便观测到显著的遗传与表型变异。所有成对FST比较中，有88%的结果具有统计学显著性；而体型相关的种群比较中，这一比例达50%。种群归属检验的高准确率证实，各褐鳟种群在基因型与表型层面均具有独特性。空间分析结果显示，种群分化程度随采样点间的河道距离、堰坝数量以及劣质生境片段长度的增加而升高，但我们未能完全厘清距离隔离与生境破碎化各自的影响效应。不同溪流的鱼类放养强度存在差异，但放养似乎并未削弱种群内部的遗传多样性。表型分化与遗传分化之间缺乏关联，这表明局部适应或针对生境异质性的表型可塑性反应发挥了重要作用。进一步分析显示，体型特征在很大程度上可由溪流地形坡度解释，而整体表型变异与各生境的水流情势高度匹配。