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.

色彩艳丽的羽毛在鸟类演化中占据核心地位，其可通过性选择与社会选择影响通讯行为，同时依托自然选择实现隐蔽保护。过往比较研究多聚焦于这类选择压力，但体色产生的底层机制同样不可或缺——其可通过限制选择可作用的色域范围，对演化进程形成约束。虹彩（iridescence）是研究选择压力与体色产生机制间相互作用的绝佳对象：同一基础模板即可生成多样色彩，而对该模板的改造可通过增加参与色彩生成的交互参数，进一步拓展色彩覆盖范围。本研究以非洲椋鸟类群为研究对象，该类群在体色产生机制、社会系统与生态位上均展现出极高多样性，借此分析其装饰性羽毛演化与羽色二态性的演化模式。研究发现，虹彩是该类群的祖先性状，且主要在雌性个体、合作繁殖物种以及体色模板稳定性较低的类群中丢失。体色产生机制间存在交互作用，是决定羽饰装饰性与复杂化程度的核心预测因子，而选择压力对其演化的影响相对微弱。但羽色二态性则受到社会系统与虹彩丢失的共同影响。本研究结果证实，在装饰性性状与雌雄二态性的演化过程中，同时考量选择压力与演化限制因素，以及二者各自发挥的不同作用，具有重要的科学意义。