Data from: Sexual selection constrains the body mass of male but not female mice

Sexual size dimorphism results when female and male body size is influenced differently by natural and sexual selection. Typically, in polygynous species larger male body size is thought to be favored in competition for mates and constraints on maximal body size are due to countervailing natural selection on either sex; however, it has been postulated that sexual selection itself may result in stabilizing selection at an optimal mass. Here we test this hypothesis by retrospectively assessing the influence of body mass, one metric of body size, on the fitness of 113 wild-derived house mice (Mus musculus) residing within ten replicate semi-natural enclosures from previous studies conducted by our laboratory. Enclosures possess similar levels of sexual selection, but relaxed natural selection, relative to natural systems. Heavier females produced more offspring, while males of intermediate mass had the highest fitness. Female results suggest that some aspect of natural selection, absent from enclosures, acts to decrease their body mass, while the upper and lower boundaries of male mass are constrained by sexual selection.

性体型二态性（Sexual size dimorphism）指当雌性与雄性的体型受到自然选择（natural selection）与性选择（sexual selection）的差异化影响时所产生的进化现象。通常认为，在一雄多雌制（polygynous）物种中，体型更大的雄性在配偶竞争中更具选择优势，而雄性最大体型的限制则源于对两性施加的反向自然选择（countervailing natural selection）；然而，有研究者提出，性选择本身可能会促使种群在最优体重处形成稳定选择（stabilizing selection）。本研究通过回溯性评估体重——即体型的衡量指标之一——对113只野生起源小家鼠（Mus musculus）适合度（fitness）的影响，对上述假说进行检验。这些小家鼠栖息于本实验室既往研究中的10个重复半自然围栏（semi-natural enclosures）种群中。相较于自然生态系统，此类围栏种群的性选择强度相近，但自然选择压力有所减弱。研究结果显示，体重更高的雌性后代数量更多，而体重处于中等水平的雄性适合度最高。雌性的研究结果表明，围栏种群中缺失的某类自然选择会抑制雌性的体重增长；而雄性体重的上下限则受到性选择的约束。