Data from: Phenotypic assortment mediates the effect of social selection in a wild beetle population

Social interactions often have major fitness consequences, but little is known about how specific interacting phenotypes affect the strength of natural selection. Social influences on the evolutionary process can be assessed using a multilevel selection approach that partitions the effects of social partner phenotypes on fitness (referred to as social or group selection) from those of the traits of a focal individual (nonsocial or individual selection). To quantify the contribution of social selection to total selection affecting a trait, the patterns of phenotypic association among interactants must also be considered. We estimated selection gradients on male body size in a wild population of forked fungus beetles (Bolitotherus cornutus). We detected positive nonsocial selection and negative social selection on body size operating through differences in copulation success, indicating that large males with small social partners had highest fitness. In addition, we found that, in low-density demes, the phenotypes of focal individuals were negatively correlated with those of their social partners. This pattern reversed the negative effect of group selection on body size and led to stronger positive selection for body size. Our results demonstrate multilevel selection in nature and stress the importance of considering social selection whenever conspecific interactions occur nonrandomly.社会互动通常对适合度（fitness）具有显著影响，但学界对特定互作表型如何调控自然选择强度的认知仍较为匮乏。可借助多级选择（multilevel selection）分析法评估社会因素对进化过程的作用：该方法可将社会伙伴表型对适合度的影响（即社会选择（social selection）或群体选择（group selection）），与焦点个体自身性状的影响（即非社会选择（nonsocial selection）或个体选择（individual selection））进行划分拆解。若要量化社会选择对某一性状总选择的贡献占比，还需充分考量互作个体间的表型关联模式。我们在野生叉形真菌甲虫（Bolitotherus cornutus）种群中，估算了雄性体型的选择梯度（selection gradients）。研究发现，体型相关的选择通过交配成功率（copulation success）差异发挥作用：存在正向非社会选择与负向社会选择，这意味着拥有较小体型社会伙伴的大型雄性个体具备最高适合度。此外，我们观测到在低密度地方种群（deme）中，焦点个体的表型与其社会伙伴的表型呈负相关关系。该模式抵消了群体选择对体型的负向调控作用，使得针对体型的正向选择强度进一步提升。本研究结果证实了自然界中多级选择的存在，并强调：当种内互动（conspecific interactions）并非随机发生时，必须将社会选择纳入考量范畴。