Data from: Selection, constraint and the evolution of coloration in African starlings

Colorful plumage plays a prominent role in evolution of birds, influencing communication (sexual/social selection) and crypsis (natural selection). Comparative studies have focused primarily upon these selective pressures, but the mechanisms underlying color production can also be important by constraining the color gamut upon which selection acts. Iridescence is particularly interesting to study the interaction between selection and color-producing mechanisms because a broad range of colors can be produced with a shared template, and innovations to this template further expand this by increasing the parameters interacting to produce colors. We examine the patterns of ornamentation and dichromatism evolution in African starlings, a group remarkably diverse in color production mechanisms, social systems, and ecologies. We find that the presence of iridescence is ancestral to the group, being predominantly lost in females and cooperative breeders, as well as species with less labile templates. Color-producing mechanisms interact and are the main predictors of plumage ornamentation and elaboration, with little influence of selective pressures in their evolution. Dichromatism, however is influenced by social system and the loss of iridescence. Our results show the importance of considering both selection and constraints, and the different roles that they may have, in the evolution of ornamentation and dimorphism.

艳丽羽饰在鸟类演化进程中发挥着核心作用，其可影响通讯过程（受性选择/社会选择（sexual/social selection）驱动）与隐蔽（受自然选择（natural selection）驱动）。过往比较研究多聚焦于这类选择压力，但色彩产生的底层机制同样至关重要——它们会限制选择可作用的色彩色域（color gamut）。虹彩羽（iridescence）在探究选择压力与色彩产生机制间的相互作用时极具研究价值，因为仅需一套共享模板即可生成多样化的色彩，而对该模板的改造还可通过增加参与色彩生成的交互参数进一步拓展色彩范围。我们以非洲椋鸟类群为研究对象，该类群在色彩产生机制、社会系统与生态特征方面均展现出显著的多样性。研究发现，虹彩羽是该类群的祖先性状，且主要在雌性个体、合作繁殖类群以及模板稳定性更强的物种中丢失。色彩产生机制之间存在相互作用，是羽饰装饰性与精细复杂度的主要预测因子，而选择压力对其演化的影响微乎其微。然而，雌雄二色性（dichromatism）则受到社会系统以及虹彩羽丢失的显著影响。本研究结果表明，在研究装饰性特征与二型性的演化过程中，同时考量选择压力与演化约束，以及二者各自承担的不同作用，具有重要的科学意义。