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因子，且被认为是驱动这些环境中种群分化的重要进化动力。然而，数量性状的种群分化可由定向自然选择、遗传漂变，或二者共同作用导致。为探究这些因素对与耐旱性相关的生态生理性状（Δ¹³C、比叶面积（SLA）、叶面积、叶片氮含量）的种群间分化的作用，我们对覆盖降水与温度梯度的13个栓皮栎（*Quercus suber* L.）种群的分子分化与数量遗传分化进行了比较。
针对树高、比叶面积与叶片氮含量的种群分化程度，远高于6个核微卫星标记检测到的分子分化水平，且与年际降水变率的气候梯度显著相关。这些结果表明：（1）这些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水不确定性的适应。
与之相反，茎径、年生长量、碳同位素判别值（水分利用效率的替代指标）的种群间分化程度较低，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或不存在。
本研究中，中性标记基因的种群间分化无法有效预测所研究的多数数量性状的分化，但叶面积是例外。叶面积的遗传分化与分子标记的分化之间仅存的相关性，源于叶面积与微卫星位点QpZAG46的关联，这暗示QpZAG46可能与调控叶面积的基因存在连锁关系。