Strength and direction of sexual direction and sex roles vary between social groups in a coral reef cardinalfish

The strength and direction of sexual selection can vary among geographically distinct populations, and within populations across time. However, spatial and temporal variability at the level of the social unit is rarely explored. Here we investigate sexual selection and sex roles in the paternally mouthbrooding and site-attached pajama cardinalfish, Sphaeramia nematoptera, where social groups can vary in size and adult sex ratio. We found that reproductive success scaled with mating success for both sexes, consistent with positive sexual selection at population level. However, within social groups, we show that adult sex-ratio and group size can influence the strength and direction of sexual selection. Our results show the Bateman gradient is steeper for females in groups with male-biased adult sex ratios and sex roles are reversed, but steeper for males in female-biased groups, and equally steep when the sex ratio is even. In medium sized groups, reproductive skew was highest for both s...性选择的强度与方向可因地理隔离的种群而异，亦会在同一种群内随时间发生变化。然而，社会单元层面的空间与时间变异却鲜有研究。本研究以父本口育且定栖的睡衣天竺鲷（Sphaeramia nematoptera）为对象，探究其性选择与性别角色；该物种的社会群体规模与成年性比均存在变异。研究发现，两性的繁殖成功率均随交配成功率提升而升高，这与种群层面的正向性选择结果一致。但在社会群体内部，成年性比与群体规模会对性选择的强度与方向产生影响。结果显示，在成年性比偏雄性的群体中，雌性的贝特曼梯度（Bateman gradient）更陡，性别角色发生反转；而在成年性比偏雌性的群体中，雄性的贝特曼梯度更陡；当性比均等时，两性的贝特曼梯度则无显著差异。在中等规模的群体中，两性的繁殖偏倚程度均达到最高……