Cramer E R A, Kaiser S A, Webster M S, Sillett T S, Ryder T B
Migratory Bird Center, Smithsonian Conservation Biology Institute, Washington, DC, USA.
Cornell Lab of Ornithology, Ithaca, NY, USA.
J Evol Biol. 2017 Dec;30(12):2177-2188. doi: 10.1111/jeb.13183. Epub 2017 Oct 25.
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 data set 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 nonsignificant, as was social selection via the body size of the males' competitors. Analysing 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.
我们对性状进化的理解建立在研究之上，这些研究考察了性状与适合度之间的相关性，其中大多数隐含地假设所有个体都经历相似的选择环境。然而，考虑到选择压力的差异，比如社会环境的变化，能够推进我们对选择如何塑造个体性状及后续适合度的理解。在本研究中，我们测试社会环境的变化是否会影响对个体表型的选择。我们应用一种新的性网络框架，将每个雄性的社会环境量化为其主要竞争对手的平均体型。我们使用一个关于黑喉蓝林莺（Setophaga caerulescens）的10年数据集，来测试对雄性体型的直接选择和社会选择，黑喉蓝林莺是一种具有领地性的物种，据推测体型会介导对配偶的竞争。我们发现，对体型的直接选择微弱且不显著，通过雄性竞争对手体型的社会选择也是如此。同时分析这两种选择类型，使我们能够坚决否定体型在该种群中雄性之间的竞争互动以及随后的雄性适合度中所起的作用。我们评估了性网络方法在实证数据中的应用，并表明在这种小型雀形目鸟类中，对于雄雄竞争而言，其他表型性状（如鸣叫特征和羽毛）可能比体型更相关。
