Badyaev A V, Hill G E, Stoehr A M, Nolan P M, McGraw K J
Division of Biological Sciences, The University of Montana, Missoula 59812-1002, USA.
Evolution. 2000 Dec;54(6):2134-44. doi: 10.1111/j.0014-3820.2000.tb01255.x.
Recent colonization of ecologically distinct areas in North America by the house finch (Carpodacus mexicanus) was accompanied by strong population divergence in sexual size dimorphism. Here we examined whether this divergence was produced by population differences in local selection pressures acting on each sex. In a long-term study of recently established populations in Alabama, Michigan, and Montana, we examined three selection episodes for each sex: selection for pairing success, overwinter survival, and within-season fecundity. Populations varied in intensity of these selection episodes, the contribution of each episode to the net selection, and in the targets of selection. Direction and intensity of selection strongly differed between sexes, and different selection episodes often favored opposite changes in morphological traits. In each population, current net selection for sexual dimorphism was highly concordant with observed sexual dimorphism--in each population, selection for dimorphism was the strongest on the most dimorphic traits. Strong directional selection on sexually dimorphic traits, and similar intensities of selection in both sexes, suggest that in each of the recently established populations, both males and females are far from their local fitness optimum, and that sexual dimorphism has arisen from adaptive responses in both sexes. Population differences in patterns of selection on dimorphism, combined with both low levels of ontogenetic integration in heritable sexually dimorphic traits and sexual dimorphism in growth patterns, may account for the close correspondence between dimorphism in selection and observed dimorphism in morphology across house finch populations.
家朱雀（Carpodacus mexicanus）近期在北美生态各异的地区定殖，伴随着性大小二态性方面强烈的种群分化。在此，我们研究了这种分化是否是由作用于两性的局部选择压力的种群差异所导致的。在一项对阿拉巴马州、密歇根州和蒙大拿州新建立种群的长期研究中，我们针对每一个性别研究了三个选择阶段：配对成功的选择、越冬存活的选择以及季节内繁殖力的选择。这些种群在这些选择阶段的强度、每个阶段对净选择的贡献以及选择目标方面存在差异。两性之间选择的方向和强度差异很大，而且不同的选择阶段常常有利于形态特征的相反变化。在每个种群中，当前对性二态性的净选择与观察到的性二态性高度一致——在每个种群中，对二态性的选择在最具二态性的特征上最为强烈。对性二态特征的强烈定向选择以及两性相似的选择强度，表明在每一个新建立的种群中，雄性和雌性都远未达到其当地的适合度最优状态，并且性二态性是由两性的适应性反应产生的。二态性选择模式的种群差异，再加上可遗传的性二态特征中低水平的个体发育整合以及生长模式中的性二态性，可能解释了家朱雀种群中选择二态性与观察到的形态二态性之间的紧密对应关系。
