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.

社会互动通常会对适合度（fitness）产生显著影响，但目前学界对特定互作表型如何影响自然选择的强度仍知之甚少。可通过多级选择（multilevel selection）分析法评估社会因素对演化过程的影响，该方法可将社会伙伴表型对适合度的影响（即社会选择或群体选择），与焦点个体自身性状的影响（即非社会选择或个体选择）分离开来。若要量化社会选择对某一性状总选择的贡献占比，还需考量互动个体间的表型关联模式。我们在野生叉角真菌甲虫（Bolitotherus cornutus）种群中，估算了雄性体型相关的选择梯度（selection gradients）。我们检测到，针对体型的选择通过交配成功率差异发挥作用，其中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交伙伴的大型雄性个体拥有最高的适合度。此外，我们发现在低密度亚种群（deme）中，焦点个体的表型与其社交伙伴的表型呈负相关。这种模式抵消了群体选择对体型的负向影响，使得针对体型的正向选择作用更强。本研究证实了自然界中存在多级选择，并强调：当种内互动并非随机发生时，必须纳入社会选择的考量维度。