Department of Biology, Duke University, PO Box 90338, Durham, NC 27708, USA.
Mol Ecol. 2011 Nov;20(22):4631-42. doi: 10.1111/j.1365-294X.2011.05310.x. Epub 2011 Oct 14.
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 geographical 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 shows 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中的一项重要任务，自然选择和遗传漂变的相对贡献长期以来一直存在争议。在这项研究中，我们使用基于回归的方法，同时估计环境适应和距离隔离对拟南芥野生近缘种 Boechera stricta 遗传变异的定量贡献。该物种内存在离散和连续遗传分化的模式。对于两个主要遗传群体之间的离散分化，环境的贡献大于地理因素，我们还发现了一个显著的环境-地理相互作用效应。在该物种的其他地区，我们发现了遗传变异的纬度梯度，仅反映了距离隔离。为了进一步证实环境选择对遗传分歧的影响，我们确定了在异域和同域地区预测局部基因型的具体环境变量。水分可用性被确定为地理区域内局部适应差异的可能原因，证实了环境适应在驱动和维持两个主要遗传群体之间遗传分化方面的作用。此外，环境-地理相互作用还通过发现水分可用性在异域和同域地区由不同的环境因素来代表得到进一步证实。总之，本研究表明，地理和环境因素共同产生了比距离隔离更强、更离散的遗传分化，而距离隔离仅产生了渐进的、渐变的遗传变异模式。这些发现强调了环境选择在塑造自然环境中物种广泛遗传变异模式方面的重要性。
