Data from: Elucidating the role of genetic drift and natural selection in cork oak differentiation regarding drought tolerance

Drought is the main selection agent in Mediterranean ecosystems and it is been suggested as an important evolutionary force responsible for population diversification in these environments. However, population divergence in quantitative traits can be driven by either directional natural selection, genetic drift or both. To investigate the roles of these forces on among-population divergence in ecophysiological traits related to drought tolerance (Δ13C, SLA, leaf size, Nmass), we compared molecular and quantitative genetic differentiation among thirteen cork oak (Quercus suber L.) populations spanning over a gradient of rainfall and temperature. Population differentiation for height, specific leaf area and leaf nitrogen content far exceeded the molecular differentiation measured by six nuclear microsatellites and was associated with the climatic gradient in among-year rainfall variation. These results suggest (1) these traits are subjected to directional selection and (2) the genetic differences among populations are partly due to adaptation to the rainfall unpredictability at the place of origin. By contrast, the low among population divergence found in stem diameter, annual growth and carbon isotopic discrimination (a surrogate for water use efficiency) and the weak association with the environmental gradient suggest low or no directional selection on these traits under dry conditions. Among-population differentiation for neutral markers was not a good predictor for differentiation regarding the quantitative traits studied here, but for leaf size. The observed correlation between the genetic differentiation for leaf size and that for molecular markers was exclusively due to the association between leaf size and microsatellite QpZAG46, which suggests a possible linkage between microsatellite QpZAG46 and genes encoding for leaf size.

干旱是地中海生态系统的主要选择动因，且被认为是驱动这类环境中种群分化的重要进化力量。然而，数量性状的种群分化既可由定向自然选择、遗传漂变单独驱动，也可由二者共同作用导致。为探究这些进化动因在与耐旱性相关的生态生理性状（Δ13C、比叶面积（Specific Leaf Area, SLA）、叶面积、单位质量叶氮含量（Nmass））的种群分化中所起的作用，本研究对覆盖降雨与温度梯度的13个栓皮栎（Quercus suber L.）种群的分子遗传分化与数量遗传分化进行了比较。植株高度、比叶面积与叶氮含量的种群分化程度远高于通过6个核微卫星标记检测到的分子分化程度，且与年际降雨波动形成的气候梯度显著相关。本研究结果表明：（1）上述性状受到定向选择作用；（2）种群间的遗传差异部分源于对原产地降雨不确定性的适应。与之相反，茎粗、年生长量及碳同位素分馏值（Δ13C，水分利用效率的替代指标）的种群分化程度较低，且与环境梯度的关联较弱，这表明在干旱条件下这些性状受到的定向选择作用较弱甚至不存在。中性标记的种群分化程度无法有效预测本研究中多数数量性状的分化，但可较好预测叶面积的分化。本研究观察到的叶面积遗传分化与分子标记遗传分化之间的相关性，仅由叶面积与微卫星位点QpZAG46之间的关联所导致，这表明微卫星位点QpZAG46可能与编码叶面积的基因存在连锁关系。