Data from: Evolution of iris colour in relation to cavity nesting and parental care in passerine birds

Strong selection pressures are known to act on animal coloration. Although many animals vary in eye colour, virtually no research has investigated the functional significance of these colour traits. Passeriformes have a range of iris colours, making them an ideal system to investigate how and why iris colour has evolved. Using phylogenetic comparative methods, we tested the hypothesis that conspicuous iris colour in passerine birds evolved in response to (a) coordination of offspring care and (b) cavity nesting, two traits thought to be involved in intra-specific gaze sensitivity. We found that iris colour and cooperative offspring care by two or more individuals evolved independently, suggesting that bright eyes are not important for coordinating parental care through eye gaze. Furthermore, we found that evolution between iris colour and nesting behaviour did occur in a dependent manner, but contrary to predictions, transitions to coloured eyes were not more frequent in cavity nesters than non-cavity nesters. Instead, our results indicate that selection away from having bright eyes was much stronger in non-cavity nesters than cavity nesters, perhaps because conspicuous eye coloration in species not concealed within a cavity would be more visible to predators.已知强烈的选择压力会对动物的色彩特征产生作用。尽管诸多动物的眼色存在变异，但目前几乎未有研究探讨这类色彩特征的功能重要性。雀形目（Passeriformes）鸟类的虹膜颜色多种多样，使其成为探究虹膜颜色演化路径与演化动因的理想研究系统。本研究采用系统发育比较方法（phylogenetic comparative methods），验证了如下假说：雀形目鸟类的醒目虹膜颜色演化，响应于两个被认为与种内视线敏感性相关的特征——（a）育幼协作行为，以及（b）洞巢营巢习性。研究结果显示，虹膜颜色与双亲及以上个体的育幼协作行为二者的演化相互独立，这表明明亮的眼部色彩并非通过视线交流协调育幼行为的关键因素。此外，本研究发现虹膜颜色与营巢行为的演化确实存在依存关联，但与理论预测不符的是，洞巢鸟类向有色虹膜演化的转变频次并未高于非洞巢鸟类。与之相反，本研究结果表明，非洞巢鸟类面临的远离明亮眼部色彩的选择压力远强于洞巢鸟类，这或许是因为未在洞穴中隐蔽的物种，其醒目的眼部色彩更容易被捕食者察觉。