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.社会互动往往会对适合度（fitness）产生重大影响，但目前对特定互动表型如何影响自然选择强度的了解仍十分有限。针对进化过程的社会影响，可借助多级选择（multilevel selection）方法进行评估：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（group selection））与焦点个体自身性状的影响（即非社会选择或个体选择）区分开来。若要量化社会选择对作用于某一性状的总选择的贡献，还需考虑互动者之间的表型关联模式。我们在野生叉角蕈甲（Bolitotherus cornutus）种群中估算了雄性体型的选择梯度（selection gradients）。研究发现，通过交配成功率差异介导的选择作用中，存在对体型的正向非社会选择与负向社会选择，这表明拥有较小体型社会伙伴的大型雄性个体拥有最高的适合度。此外，我们发现在低密度同类群（demes）中，焦点个体的表型与其社会伙伴的表型呈负相关。这种模式逆转了群体选择对体型的负面影响，并强化了针对体型的正向选择。我们的研究结果证实了自然界中存在多级选择，并强调了在同种互动非随机发生时，考虑社会选择的重要性。