Data from: Homage to Bateman: sex roles predict sex differences in sexual selection

Classic sex role theory predicts that sexual selection should be stronger in males in taxa showing conventional sex roles and stronger in females in role reversed mating systems. To test this very central prediction and to assess the utility of different measures of sexual selection, we estimated sexual selection in both sexes in four seed beetle species with divergent sex roles using a novel experimental design. We found that sexual selection was sizeable in females and the strength of sexual selection was similar in females and males in role-reversed species. Sexual selection was overall significantly stronger in males than in females and residual selection formed a substantial component of net selection in both sexes. Furthermore, sexual selection in females was stronger in role-reversed species compared to species with conventional sex roles. Variance-based measures of sexual selection (the Bateman gradient and selection opportunities) were better predictors of sexual dimorphism in reproductive behavior and morphology across species compared to trait-based measures (selection differentials). Our results highlight the importance of using assays that incorporate components of fitness manifested after mating. We suggest that the Bateman gradient is generally the most informative measure of the strength of sexual selection in comparisons across sexes and/or species.

经典性角色（sex roles）理论预测，在呈现传统性角色的类群（taxa）中，雄性的性选择（sexual selection）强度更高；而在性角色反转的交配系统中，雌性的性选择强度更高。为验证这一核心预测，并评估不同性选择度量方法的实用性，我们采用全新实验设计，对4种性角色存在分化的种子甲虫物种的两性性选择强度进行了估算。研究发现，雌性的性选择强度可观；在性角色反转的物种中，雌雄两性的性选择强度相近。整体而言，雄性的性选择强度显著高于雌性；且残差选择（residual selection）在两性的净选择（net selection）中均占据重要比重。此外，相较于传统性角色物种，性角色反转物种的雌性性选择强度更高。相较于基于性状的度量方法（选择差（selection differentials）），基于方差的性选择度量方法（贝特曼梯度（Bateman gradient）与选择机会（selection opportunities））更能预测不同物种间繁殖行为与形态特征的性二态性（sexual dimorphism）。本研究结果凸显了纳入交配后表现的适合度（fitness）组分的实验方法的重要性。我们提出，在跨性别或跨物种的性选择强度比较中，贝特曼梯度通常是最具信息价值的度量指标。