Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada.
J Evol Biol. 2012 Jul;25(7):1233-42. doi: 10.1111/j.1420-9101.2012.02522.x. Epub 2012 May 3.
Ornamental traits function by improving attractiveness and are generally presumed to experience directional selection for mating success. However, given the greater investment of females in offspring than males, female-specific ornaments can in theory signal fecundity yet be constrained by fecundity costs. Theoretical work predicts that such constraints can lead to stabilizing selection via male choice for intermediately ornamented females. Female dance flies Rhamphomyia longicauda (Diptera: Empididae) display two female-specific ornaments in mating swarms - inflatable abdominal sacs and pinnate tibial scales. We investigated the intensity and form of sexual selection on female traits including ornaments and found no evidence for directional sexual selection. Instead, we found marginally nonsignificant quadratic selection for all three measures of ornament expression. Canonical analysis confirmed that the strongest vectors of nonlinear selection were associated with ornamental traits, although the significance of the quadratic coefficients associated with these vectors depended on the statistical approach. Direct Mitchell-Olds and Shaw tests for the location of the maximum fitted fitness value for both raw morphological traits and canonical axes revealed only one marginally nonsignificant result for the multivariate axis loading most heavily on pinnate leg scales. Together, these results provide the first tentative support for stabilizing selection on female-specific ornaments.
装饰性特征通过提高吸引力起作用，通常被认为会经历方向性选择以提高交配成功率。然而，鉴于雌性在后代上的投资大于雄性，雌性特有的装饰物理论上可以信号繁殖力，但受到繁殖力成本的限制。理论工作预测，这种限制可以通过雄性对中等装饰的雌性的选择，导致稳定选择。交配群中的雌性舞蝇 Rhamphomyia longicauda（双翅目：Empididae）展示了两种雌性特有的装饰物——可充气的腹部囊和羽状的胫骨鳞片。我们调查了包括装饰物在内的雌性特征的强度和形式的性选择，没有发现方向性性选择的证据。相反，我们发现所有三种装饰物表达的测量值都存在边缘非显著二次选择。典范分析证实，与装饰物相关的最强非线性选择向量，尽管与这些向量相关的二次系数的显著性取决于统计方法。直接的 Mitchell-Olds 和 Shaw 测试表明，无论是原始形态特征还是典范轴，最大拟合适应值的位置，只有一个与羽状腿鳞片负载最重的多元轴加载的结果是边缘非显著的。总的来说，这些结果首次为雌性特有的装饰物提供了稳定选择的初步支持。
