Badyaev A V, Martin T E
Division of Biological Sciences, University of Montana, Missoula, 59812-1002, USA.
Evolution. 2000 Jun;54(3):987-97. doi: 10.1111/j.0014-3820.2000.tb00098.x.
Sexual dimorphism is thought to have evolved in response to selection pressures that differ between males and females. Our aim in this study was to determine the role of current net selection in shaping and maintaining contemporary sexual dimorphism in a recently established population of the house finch (Carpodacus mexicanus) in Montana. We found strong differences between sexes in direction of selection on sexually dimorphic traits, significant heritabilities of these traits, and a close congruence between current selection and observed sexual dimorphism in Montana house finches. Strong directional selection on sexually dimorphic traits and similar intensities of selection in each sex suggested that sexual dimorphism arises from adaptive responses in males and females, with both sexes being far from their local fitness optimum. This pattern is expected when a recently established population experiences continuous immigration from ecologically distinct areas of a species range or as a result of widely fluctuating selection pressures, as found in our study. Strong and sexually dimorphic selection pressures on heritable morphological traits, in combination with low phenotypic and genetic covariation among these traits during growth, may have accounted for close congruence between current selection and observed sexual dimorphism in the house finch. This conclusion is consistent with the profound adaptive population divergence in sexual dimorphism that accompanied very successful colonization of most of the North America by the house finch over the last 50 years.
性二态性被认为是在雄性和雌性不同的选择压力作用下进化而来的。我们这项研究的目的是确定当前净选择在塑造和维持蒙大拿州一个新建立的家朱雀（Carpodacus mexicanus）种群的当代性二态性方面所起的作用。我们发现，在对性二态性状的选择方向上，两性之间存在显著差异，这些性状具有显著的遗传力，并且当前的选择与蒙大拿州家朱雀中观察到的性二态性密切一致。对性二态性状的强烈定向选择以及两性中相似的选择强度表明，性二态性源于雄性和雌性的适应性反应，两性都远未达到其当地的适合度最优状态。当一个新建立的种群经历来自物种分布范围内生态不同区域的持续迁入，或者如我们研究中所发现的，由于选择压力广泛波动时，就会出现这种模式。对可遗传形态性状的强烈且具有性二态性的选择压力，再加上这些性状在生长过程中较低的表型和遗传协方差，可能解释了当前选择与家朱雀中观察到的性二态性之间的密切一致。这一结论与过去50年家朱雀在北美大部分地区非常成功的定殖过程中所伴随的性二态性方面深刻的适应性种群分化是一致的。
