Data from: Characterizing selection in black-throated blue warblers using a sexual network approach

Our understanding of trait evolution is built upon studies that examine the correlation between traits and fitness, most of which implicitly assume all individuals experience similar selective environments. However, accounting for differences in selective pressures, such as variation in the social environment, can advance our understanding of how selection shapes individual traits and subsequent fitness. In this study, we test whether variation in the social environment affects selection on individual phenotype. We apply a new sexual network framework to quantify each male's social environment as the mean body size of his primary competitors. We test for direct and social selection on male body size using a 10-year dataset on black-throated blue warblers (Setophaga caerulescens), a territorial species for which body size is hypothesized to mediate competition for mates. We found that direct selection on body size was weak and non-significant, as was social selection via the body size of the males’ competitors. Analyzing both types of selection simultaneously allows us to firmly reject a role for body size in competitive interactions between males and subsequent male fitness in this population. We evaluate the application of the sexual network approach to empirical data, and suggest that other phenotypic traits such as song characteristics and plumage may be more relevant than body size for male-male competition in this small passerine bird.

我们对性状演化的认知，建立于探究性状与适合度之间相关性的研究之上，而这类研究大多默认所有个体所处的选择环境均相似。然而，若将选择压力的差异——例如社会环境的变异——纳入考量，则能深化我们对选择如何塑造个体性状及后续适合度的认知。本研究旨在检验社会环境的变异是否会影响个体表型所受的选择。我们采用全新的性网络框架，将每只雄鸟的社会环境量化为其主要竞争者的平均体型。我们依托一项针对黑喉蓝林莺（Setophaga caerulescens）的10年数据集，检验雄鸟体型所受的直接选择与社会选择；该物种为领地性鸟类，学界假设其体型可介导配偶竞争。研究结果显示，针对体型的直接选择效应微弱且不显著，通过竞争者体型介导的社会选择亦是如此。同时分析两类选择的效应，使我们得以确凿地否定：在该种群中，体型在雄鸟间的竞争互动以及后续雄鸟适合度中发挥作用。我们评估了性网络方法在经验数据中的应用，并提出：对于这种小型雀形目鸟类的雄-雄竞争而言，鸣声特征、羽色等其他表型性状或许比体型更为关键。