Garcia Roberto, Siepielski Adam M, Benkman Craig W
Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071 USA.
Am J Bot. 2009 May;96(5):1050-4. doi: 10.3732/ajb.0800298. Epub 2009 Apr 16.
Phenotypic variation among individuals is necessary for natural selection to operate and is therefore essential for adaptive evolution. However, extensive variation within individuals can mask variation among individuals and weaken the potential for selection. Here we quantify variation among and within individuals in female cone and seed traits of whitebark pine (Pinus albicaulis). In many plants, the production of numerous reproductive structures creates the potential for considerable variation within a plant, but these same traits should also undergo strong selection because of their direct link to plant fitness. We found about twice as much variation among individuals (overall mean = 65.3 ± 4.5% SE) than within individuals (overall mean = 34.7 ± 4.5%). One only needs to sample three to five cones per tree to accurately assess variation among trees in most cone and seed traits. The ease at which trees can be assessed helps account for the strong and consistent patterns of phenotypic selection exerted by seed predators and dispersers of whitebark pine and many other conifers. In contrast, the few traits where variation within trees equaled or exceeded that among trees underwent weak if any phenotypic selection.
个体间的表型变异是自然选择发挥作用的必要条件，因此对于适应性进化至关重要。然而，个体内部的广泛变异可能会掩盖个体间的变异，并削弱选择的潜力。在这里，我们对白皮松（Pinus albicaulis）雌球果和种子性状的个体间和个体内变异进行了量化。在许多植物中，大量生殖结构的产生使得植物内部存在相当大变异的可能性，但由于这些性状与植物适合度直接相关，它们也应该受到强烈的选择。我们发现个体间的变异（总体均值 = 65.3 ± 4.5% 标准误）大约是个体内变异（总体均值 = 34.7 ± 4.5%）的两倍。对于大多数球果和种子性状而言，每棵树只需采集三到五个球果就能准确评估树间的变异。评估树木的便捷性有助于解释白皮松和许多其他针叶树的种子捕食者及传播者所施加的强烈且一致的表型选择模式。相比之下，树木内部变异等于或超过树间变异的少数性状，如果有表型选择的话，也很微弱。
