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.阐明影响遗传分化的因素是生物学领域的核心研究课题，自然选择与遗传漂变的相对贡献长期以来一直存在学术争议。本研究采用基于回归的统计方法，同时估算了环境适应和距离隔离（isolation by distance）对拟南芥野生近缘种硬叶南芥（Boechera stricta）遗传变异的量化贡献。该物种内部同时存在离散型与连续型两种遗传分化模式。针对两个主要遗传类群间的离散分化，环境因素的贡献度显著高于地理因素，本研究还鉴定出显著的环境-地理交互效应。在该物种分布范围的其余区域，我们发现仅由距离隔离驱动的遗传变异呈现纬度梯度格局。为进一步验证环境选择对遗传分化的作用，我们鉴定出可预测异域（allopatric）与同域（sympatric）分布区域内本地基因型的特定环境变量。在两个地理区域中，水分可利用性均被鉴定为驱动本地适应性分化的潜在诱因，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关键作用。此外，研究发现水分可利用性在异域与同域区域由不同环境因子表征，这进一步验证了环境-地理的交互效应。综上，本研究表明地理与环境因子共同作用所产生的遗传分化，比仅由距离隔离导致的遗传分化更强且更具离散性——后者仅能产生渐进式的梯度遗传变异格局。上述研究结果强调了环境选择在塑造自然环境中物种整体遗传变异格局方面的重要性。