Stowe Kirk A, Sork Victoria L, Farrell Andrew W
Department of Biology, University of Missouri-St. Louis, 8001 Natural Bridge Road, 63121-4499, St. Louis, MO, USA.
Oecologia. 1994 Dec;100(3):309-315. doi: 10.1007/BF00316959.
The phenotypic expression of quantitative characters is a function of the individual's genotype and the environment in which it is measured. In a previous reciprocal transplant study, we found that patterns of genetic differences in resistance to herbivores among adjacent subpopulations of northern red oak (Quercus rubra L.), were consistent with a local adaptation hypothesis. The goal of this study was to determine if variation in water availability may have been a mechanism responsible for these previously observed patterns. In 1989 a common garden study was initiated using acorns from maternal trees occupying either a north- or south-facing slope microhabitat in an oak-hickory forest in east central Missouri, USA. The seedlings were grown under one of two water treatments, irrigated or natural. In 1992, we utilized this experiment to examine the quantitative character of the percentage of leaf area damaged by herbivores, which is a measure of the phenotypically expressed level of resistance. Specifically, we made three predictions: (1) because northern red oak seem to grow best in mesic environments, seedlings receiving more water should show greater resistance to herbivores; (2) if the subpopulations from north- and south-facing slope microhabitats are genetically differentiated with respect to the quantitative character of resistance to herbivores, then there will be a significant effect of maternal slope microhabitat on the percentage of leaf area damaged; and (3) if the pattern of resistance to herbivores found among subpopulations reflects local adaptation to moisture levels in their own microhabitat, then we would expect to find a significant maternal slope microhabitat by water treatment interaction, with north-facing slope seedlings incurring less damage in the wetter (irrigated) treatment and south-facing slope seedlings incurring less damage in the drier (natural) treatment. Our data supported the first two predictions: seedlings in the irrigated treatment showed a significantly lower percentage of leaf area damage than those in the natural treatment, and the percentage of leaf area damaged was significantly lower on seedlings from maternal plants occupying the north-facing slope microhabitat. However, we found no significant interaction between maternal slope microhabitat and water treatment. These findings demonstrate that northern red oak supbopulations respond phenotypically to water availability, but this factor does not appear to be the underlying mechanism behind the previously observed local adaptation expressed as resistance to herbivores.
数量性状的表型表达是个体基因型以及测量该性状时所处环境的函数。在之前的一项 reciprocal transplant 研究中，我们发现北方红栎（Quercus rubra L.）相邻亚种群间对食草动物抗性的遗传差异模式，与局部适应假说相符。本研究的目的是确定水分可利用性的差异是否可能是造成这些先前观察到的模式的一种机制。1989年，在美国密苏里州中东部一片橡树林山核桃林中，利用来自占据北坡或南坡微生境的母树的橡子开展了一项共同园试验。幼苗在两种水分处理之一（灌溉或自然状态）下生长。1992年，我们利用该实验研究了食草动物造成的叶面积受损百分比这一数量性状，它是表型表达的抗性水平的一种度量。具体而言，我们做出了三个预测：（1）由于北方红栎似乎在中生环境中生长最佳，接受更多水分的幼苗应表现出对食草动物更强的抗性；（2）如果来自北坡和南坡微生境的亚种群在对食草动物抗性的数量性状上存在遗传分化，那么母本坡向微生境对叶面积受损百分比将有显著影响；（3）如果在亚种群间发现的对食草动物的抗性模式反映了对其自身微生境中水分水平的局部适应，那么我们预期会发现母本坡向微生境与水分处理之间存在显著的交互作用，即北坡幼苗在较湿润（灌溉）处理下受损较少，而南坡幼苗在较干燥（自然）处理下受损较少。我们的数据支持了前两个预测：灌溉处理下的幼苗叶面积受损百分比显著低于自然处理下的幼苗，且来自占据北坡微生境的母本植物的幼苗叶面积受损百分比显著更低。然而，我们未发现母本坡向微生境与水分处理之间存在显著的交互作用。这些发现表明北方红栎亚种群在表型上对水分可利用性有响应，但该因素似乎并非先前观察到的以对食草动物的抗性表现出来的局部适应背后的潜在机制。
