Moore Allen J
Department of Cell Biology and Anatomy, Northwestern University Medical School, 303 East Chicago Avenue, Chicago, IL, 60611.
Evolution. 1990 Mar;44(2):315-331. doi: 10.1111/j.1558-5646.1990.tb05201.x.
Libellula luctuosa, a pond dragonfly found in eastern North America, is apparently sexually dimorphic. Previous studies of the mating behavior in this species suggested that both male-male competition and female mate choice are important influences. Males compete for territories, where they attract females and where mating occurs. Female behavior influences both the copulation success and the fertilization success of males. Because of temporal and spatial separation of these episodes of sexual selection, multivariate and nonparametric statistical techniques could be used to investigate the influence of components of sexual selection on various sexually dimorphic traits. Sexual dimorphism in L. luctuosa was first quantified; then the direct effects and the form of selection were estimated. Sexually dimorphic wing size, body size, wing coloration, and body coloration are distributed either continuously or discontinuously between the sexes in L. luctuosa. These traits have apparently diverged between the sexes as a result of directional sexual selection. Body size is further influenced by stabilizing selection. Intrasexual selection (success in gaining access to a territory) and intersexual selection (success in copulation and fertilization) can influence the same or different sexually dimorphic characters. Body size is influenced by directional selection during the intrasexual phase of sexual selection and is also influenced by stabilizing selection during intersexual selection. The size of the brown wing patch is influenced by directional selection, primarily during the intersexual phase of sexual selection. There is directional selection on the white wing patch during both phases. Thus, the different proximate mechanisms of sexual selection may jointly or separately affect the evolution of sexually dimorphic characters. Further empirical and theoretical investigations into the differences in the effects of intrasexual selection and intersexual selection are needed to clarify the circumstances leading to separate consequences of these two mechanisms of sexual selection.
北美东部发现的一种池塘蜻蜓——悲色蟌（Libellula luctuosa）显然具有两性异形。此前对该物种交配行为的研究表明，雄性间竞争和雌性配偶选择都是重要影响因素。雄性争夺领地，在领地中吸引雌性并进行交配。雌性行为会影响雄性的交配成功率和受精成功率。由于这些性选择事件在时间和空间上的分离，可以使用多变量和非参数统计技术来研究性选择各组成部分对各种两性异形特征的影响。首先对悲色蟌的两性异形进行了量化；然后估计了直接影响和选择形式。在悲色蟌中，两性异形的翅大小、身体大小、翅色和体色在两性之间呈连续或不连续分布。由于定向性选择，这些特征在两性之间显然已经分化。身体大小还受到稳定选择的进一步影响。同性选择（获得领地的成功）和异性选择（交配和受精的成功）可以影响相同或不同的两性异形特征。身体大小在性选择的同性阶段受到定向选择的影响，在异性选择阶段也受到稳定选择的影响。棕色翅斑的大小受到定向选择的影响，主要是在性选择的异性阶段。在两个阶段对白翅斑都有定向选择。因此，性选择的不同近端机制可能共同或分别影响两性异形特征的进化。需要对同性选择和异性选择影响的差异进行进一步的实证和理论研究，以阐明导致这两种性选择机制产生不同后果的情况。
