Fisher weevil data.zip from Social selection is density dependent but makes little contribution to total selection in New Zealand giraffe weevils

Social selection occurs when traits of interaction partners influence an individual's fitness and can alter total selection strength. However, we have little idea of what factors influence social selection's strength. Further, social selection only contributes to overall selection when there is phenotypic assortment, but simultaneous estimates of social selection and phenotypic assortment are rare. Here, we estimated social selection on body size in a wild population of New Zealand giraffe weevils (<i>Lasiorhynchus barbicornis</i>). We measured phenotypic assortment by body size and tested whether social selection varied with sex ratio, density and interacted with the body size of the focal individual. Social selection was limited and unaffected by sex ratio or the size of the focal individual. However, at high densities social selection was negative for both sexes, consistent with size-based competitive interactions for access to mates. Phenotypic assortment was always close to zero, indicating negative social selection at high densities will not impede the evolution of larger body sizes. Despite its predicted importance, social selection may only influence evolutionary change in specific contexts, leaving direct selection to drive evolutionary change.社会选择（social selection）指当互动伙伴的性状影响个体适合度，并可改变总选择强度时发生的选择过程。然而，目前学界对哪些因素会影响社会选择的强度仍知之甚少。进一步而言，仅当存在表型关联（phenotypic assortment）时，社会选择才会对总选择产生贡献，但同时估算社会选择与表型关联的研究仍较为罕见。本研究针对新西兰长颈鹿象鼻虫（*Lasiorhynchus barbicornis*）的野生种群，估算了其体型相关的社会选择强度。我们通过体型指标量化了种群的表型关联，并检验了社会选择强度是否随性比、种群密度发生变化，以及是否与焦点个体的体型存在交互效应。研究结果显示，社会选择整体强度较弱，且不受性比或焦点个体体型的影响。但在高种群密度下，雌雄个体的社会选择均呈负值，这与基于体型的配偶竞争交互作用相符。种群的表型关联始终接近零，这表明高密环境下的负向社会选择不会阻碍体型增大的演化进程。尽管社会选择被预测具有重要的演化作用，但其仅能在特定情境下影响演化改变，直接选择仍是驱动演化的核心动力。