Data from: Local population density and group composition influence signal-preference relationships in Enchenopa treehoppers (Hemiptera: Membracidae)

Many animals exhibit social plasticity—changes in phenotype or behavior in response to experience with conspecifics—that change how evolutionary processes like sexual selection play out. Here, we asked whether social plasticity arising from variation in local population density in male advertisement signals and female mate preferences influences the form of sexual selection. We manipulated local density and determined whether this changed how the distribution of male signals overlapped with female preferences—i.e., the signal-mate preference relationship. We specifically look at the shape of female mate preference functions, which, when compared to signal distributions, provide hypotheses about the form of sexual selection. We used Enchenopa binotata treehoppers, a group of plant feeding insects that exhibit natural variation in local densities across individual host plants, populations, species, and years. We measured male signal frequency and female preference functions across the density treatments. We found that male signals varied across local social groups, but not according to local density. By contrast, female preferences varied with local density—favoring higher signal frequencies in denser environments. Thus, local density changes the signal-preference relationship and, consequently, the expected form of sexual selection. We found no influence of sex ratio on the signal-preference relationship. Our findings suggest that plasticity arising from variation in local group density and composition can alter the form of sexual selection with potentially important consequences both for the maintenance of variation and for speciation.诸多动物均展现出社会可塑性（social plasticity）——即因与同种个体的交互经历而发生的表型或行为改变——这类改变会影响性选择等进化过程的运作模式。本研究旨在探究：由雄性广告信号与雌性配偶偏好的局域种群密度差异所引发的社会可塑性，是否会对性选择的形式产生影响。我们通过操控局域种群密度，探究该操作是否改变了雄性信号分布与雌性配偶偏好的匹配程度，即信号-配偶偏好关系。我们重点关注雌性配偶偏好函数的形态，将其与信号分布对比后，可推导性选择形式的相关假说。本研究以二点刻胸角蝉（Enchenopa binotata）为实验对象——这类植食性昆虫的局域种群密度在单个寄主植物、种群、物种以及不同年份间均存在自然差异。我们在不同密度处理组中测量了雄性信号频率与雌性配偶偏好函数。研究结果显示：雄性信号在局域社会群间存在差异，但并未随局域密度发生规律性变化；与之相反，雌性配偶偏好随局域密度发生改变——在种群更密集的环境中，雌性更偏好频率更高的雄性信号。由此可见，局域密度会改变信号-偏好关系，进而改变性选择的预期形式。我们未发现性比对信号-偏好关系存在影响。本研究结果表明：由局域种群密度与组成差异所引发的可塑性，能够改变性选择的形式，这对维持种群变异与物种形成过程均可能产生重要影响。