Dudley Susan A
Department of Ecology and Evolution, University of Chicago, Chicago, Illinois, 60637.
Evolution. 1996 Feb;50(1):92-102. doi: 10.1111/j.1558-5646.1996.tb04475.x.
I used phenotypic selection analysis to test the prediction from functional and comparative studies of plants that smaller leaves and more efficient water use are adaptive in drier environments. I measured selection gradients on leaf size and instantaneous water-use efficiency (a measure of carbon gain per unit water loss) in experimental populations of Cakile edentula var. lacustris placed into wet and dry environments in the field. Linear and nonlinear selection differed significantly between the two environments as predicted. Water-use efficiency was selected to be higher, and leaf area was selected toward a small intermediate optimum, in the dry environment. There was also significant positive correlational selection on water-use efficiency and leaf size, suggesting that the optimum leaf size in the dry environment is greater for plants with higher water-use efficiency. In contrast, neither leaf size nor water-use efficiency were selected in the wet environment, though larger leaves resulted in greater vegetative biomass. Path analysis of the linear selection gradients found that water-use efficiency affected plant fitness primarily because it increased vegetative biomass, as suggested by the hypotheses about the function of physiological traits. These results were not only consistent with the functional hypotheses but also with the observed genetic differentiation in water-use efficiency and leaf size between wet and dry site populations.
我采用表型选择分析来检验植物功能和比较研究的预测结果，即较小的叶片和更高效的水分利用在更干旱的环境中具有适应性。我在野外将海滨刺芹湖生变种实验种群置于湿润和干旱环境中，测量了叶片大小和瞬时水分利用效率（单位水分损失的碳增益量度）的选择梯度。正如预测的那样，两种环境下的线性和非线性选择存在显著差异。在干旱环境中，水分利用效率被选择为更高，叶片面积被选择趋向于一个小的中间最优值。水分利用效率和叶片大小之间也存在显著的正相关选择，这表明在干旱环境中，水分利用效率较高的植物的最优叶片大小更大。相比之下，在湿润环境中，叶片大小和水分利用效率均未被选择，尽管较大的叶片会产生更大的营养生物量。对线性选择梯度的通径分析发现，水分利用效率影响植物适合度主要是因为它增加了营养生物量，这与关于生理性状功能的假设一致。这些结果不仅与功能假设相符，也与在湿润和干旱地点种群之间观察到的水分利用效率和叶片大小的遗传分化相符。
