Data from: Quantifying effects of environmental and geographical factors on patterns of genetic differentiation

Elucidating the factors influencing genetic differentiation is an important task in biology, and the relative contribution from natural selection and genetic drift has long been debated. In this study, we used a regression-based approach to simultaneously estimate the quantitative contributions of environmental adaptation and isolation by distance on genetic variation in Boechera stricta, a wild relative of Arabidopsis. Patterns of discrete and continuous genetic differentiation coexist within this species. For the discrete differentiation between two major genetic groups, environment has larger contribution than geography, and we also identified a significant environment-by-geography interaction effect. Elsewhere in the species range, we found a latitudinal cline of genetic variation reflecting only isolation by distance. To further confirm the effect of environmental selection on genetic divergence, we identified the specific environmental variables predicting local genotypes in allopatric and sympatric regions. Water availability was identified as the possible cause of differential local adaptation in both geographic regions, confirming the role of environmental adaptation in driving and maintaining genetic differentiation between the two major genetic groups. In addition, the environment-by-geography interaction is further confirmed by the finding that water availability is represented by different environmental factors in the allopatric and sympatric regions. In conclusion, this study found that geographical and environmental factors together created stronger and more discrete genetic differentiation than isolation by distance alone, which only produced a gradual, clinal pattern of genetic variation. These findings emphasize the importance of environmental selection in shaping patterns of species-wide genetic variation in the natural environment.

阐明影响遗传分化（genetic differentiation）的因素是生物学领域的重要研究课题，而自然选择（natural selection）与遗传漂变（genetic drift）的相对贡献长期以来一直存在争议。本研究采用基于回归的分析方法（regression-based approach），同时估算了环境适应（environmental adaptation）与距离隔离（isolation by distance）对拟南芥野生近缘种硬毛南芥（Boechera stricta）遗传变异（genetic variation）的定量贡献。该物种内同时存在离散型与连续型两类遗传分化模式。针对两个主要遗传类群间的离散分化，环境因素的贡献大于地理因素，本研究还检测到显著的环境-地理交互效应（environment-by-geography interaction）。在该物种分布范围的其他区域，本研究观察到仅由距离隔离驱动的遗传变异纬度梯度格局（latitudinal cline）。为进一步验证环境选择（environmental selection）对遗传分化的作用，本研究筛选出了可预测异域（allopatric）与同域（sympatric）分布区本地基因型的特定环境变量。研究发现，水分可获得性是两个地理区域内本地适应性分化的潜在驱动因素，这证实了环境适应在推动并维持两个主要遗传类群间遗传分化中的作用。此外，研究发现在异域与同域分布区中，水分可获得性由不同的环境因子表征，这进一步验证了环境-地理交互效应的存在。综上，本研究表明，与仅靠距离隔离所产生的渐进式梯度遗传变异格局相比，地理与环境因子共同作用可形成更强且更具离散性的遗传分化模式。本研究结果凸显了环境选择在塑造自然环境中物种种群整体遗传变异格局方面的重要性。