Data from: Adaptive genetic divergence along narrow environmental gradients in four stream insects

A central question linking ecology with evolutionary biology is how environmental heterogeneity can drive adaptive genetic divergence among populations. We examined adaptive divergence of four stream insects from six adjacent catchments in Japan by combining field measures of habitat and resource components with genome scans of non-neutral Amplified Fragment Length Polymorphism (AFLP) loci. Neutral genetic variation was used to measure gene flow and non-neutral genetic variation was used to test for adaptive divergence. We identified the environmental characteristics contributing to divergence by comparing genetic distances at non-neutral loci between sites with Euclidean distances for each of 15 environmental variables. Comparisons were made using partial Mantel tests to control for geographic distance. In all four species, we found strong evidence for non-neutral divergence along environmental gradients at between 6 and 21 loci per species. The relative contribution of these environmental variables to each species' ecological niche was quantified as the specialization index, S, based on ecological data. In each species, the variable most significantly correlated with genetic distance at non-neutral loci was the same variable along which each species was most narrowly distributed (i.e., highest S). These were gradients of elevation (two species), chlorophyll-a, and ammonia-nitrogen. This adaptive divergence occurred in the face of ongoing gene flow (Fst = 0.01–0.04), indicating that selection was strong enough to overcome homogenization at the landscape scale. Our results suggest that adaptive divergence is pronounced, occurs along different environmental gradients for different species, and may consistently occur along the narrowest components of species' niche.连接生态学与进化生物学的核心问题之一，是环境异质性如何推动种群间的适应性遗传分化。本研究以日本6个相邻集水区的4种溪流昆虫为研究对象，结合栖息地与资源组分的野外实测数据，以及非中性扩增片段长度多态性（Amplified Fragment Length Polymorphism, AFLP）位点的基因组扫描结果，分析其适应性遗传分化模式。研究中利用中性遗传变异评估种群间的基因流水平，同时借助非中性遗传变异检验适应性遗传分化的存在。本研究通过比较各采样点间非中性位点的遗传距离与15种环境变量各自的欧氏距离，识别驱动遗传分化的环境特征；并采用偏曼特尔检验（partial Mantel test）控制地理距离的混杂效应。在4个物种中均检测到显著的非中性分化信号，每个物种对应6至21个受环境梯度影响的位点。基于野外生态数据，我们将各环境变量对物种生态位的相对贡献量化为特化指数S（specialization index）。对于每个物种而言，与非中性位点遗传距离显著相关的环境变量，恰恰是该物种分布范围最狭窄（即特化指数S最高）的环境梯度变量。这些环境梯度分别为海拔（对应2个物种）、叶绿素a以及氨氮。尽管存在持续的基因流（Fst值为0.01~0.04），该适应性分化仍得以发生，这表明选择作用强度足以抵消景观尺度下的遗传均质化效应。本研究结果表明，适应性遗传分化现象显著存在，且不同物种的分化沿不同的环境梯度进行，同时分化大概率发生在物种生态位中分布范围最狭窄的组分上。