The mobility hypothesis argues that species in which males compete for mates in scrambles often exhibit female-biased size dimorphism because smaller male body size should increase male mobility and success in searching for mates. Sexual dimorphism can be further exaggerated if fecundity or sexual selection concurrently selects for larger female size. Scramble competition can select for trait characteristics that optimize locomotion; for example, long and slender wings should be favored if aerial speed is important to mating success. I tested these predictions in the scrambling Japanese beetle (Popillia japonica), a female-biased size dimorphic insect pest that is invasive to North America. Multivariate selection analyses support the prediction that smaller body size and larger wings in males benefit their mating success. My analyses also revealed significant selection for larger wings in females but, contrary to prediction, direct sexual selection favors smaller body size in females. These results support the mobility hypothesis and partially explain the evolution of female-biased size dimorphism in this species. Sexual selection favored rounder bodies in females and more tapered bodies in males, whereas, in both sexes, the effect of wing shape appears less important to fitness than wing size.

中文翻译：

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日本甲虫（Popillia japonica）大小和形状的性别选择

流动性假设认为，雄性争夺配偶的物种通常表现出雌性偏向的大小二态性，因为较小的雄性体型应该增加雄性的动性并成功寻找配偶。如果同时进行生殖力或性别选择以选择更大的雌性，则可能进一步夸大性二态性。争夺比赛可以选择优化运动的性格特征。例如，如果空速对于成功配对很重要，则应优先选择细长的机翼。我在混乱的日本甲虫（Popillia japonica）中测试了这些预测），是一种偏向北美的雌性大小的双态昆虫害虫。多变量选择分析支持以下预测：雄性较小的体型和较大的翅膀有利于其交配成功。我的分析还表明，对雌性较大翅膀的选择显着，但与预测相反，直接的性选择有利于雌性较小的体型。这些结果支持了流动性假说，并部分解释了该物种中女性偏向大小二态性的进化。性别选择有利于雌性的圆形体和雄性的锥形体，而在两种性别中，机翼形状的影响对身体健康的重要性似乎都比机翼大小重要。