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核心研究课题之一，而自然选择与遗传漂变（genetic drift）的相对贡献长期以来备受学界争论。本研究采用基于回归的分析方法，同时量化了环境适应（environmental adaptation）以及距离隔离（isolation by distance）对拟南芥野生近缘种硬枝南芥（Boechera stricta）遗传变异（genetic variation）的影响。该物种种群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型分化，环境因素的贡献度高于地理因素，本研究还检测到了显著的环境-地理交互（environment-by-geography interaction）效应。在该物种分布区的其余区域，本研究发现了仅由距离隔离驱动的遗传变异纬度梯度（latitudinal cline）格局。为进一步验证环境选择（environmental selection）对遗传分化（genetic divergence）的作用，本研究筛选出了可预测异域（allopatric）与同域（sympatric）区域内本地基因型的特异性环境变量。研究证实水分可利用性（water availability）是两个地理区域内本地适应性分化的潜在诱因，这验证了环境适应在驱动并维持两个主要遗传类群间遗传分化中的核心作用。此外，本研究发现在异域与同域区域内，水分可利用性由不同的环境因子所表征，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，相较于仅依靠距离隔离所产生的渐进式梯度遗传变异格局，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。上述研究结果强调了环境选择在塑造自然环境中物种种群水平遗传变异格局方面的重要意义。