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.学界已知强烈的选择压力会对动物的色彩特征产生作用。尽管诸多动物的眼部色彩存在差异，但目前几乎尚无研究探讨此类色彩特征的功能意义。雀形目（Passeriformes）鸟类具有多样的虹膜色彩，这使其成为探究虹膜色彩演化路径与演化动因的理想研究体系。本研究采用系统发育比较方法（phylogenetic comparative methods），对雀形目鸟类的醒目虹膜色彩演化假说进行了检验：该假说认为，雀形目鸟类的醒目虹膜色彩演化是为了响应两类与种内视线敏感性相关的特征——（a）合作育幼行为，以及（b）树洞筑巢习性。研究结果显示，虹膜色彩与双亲及以上个体的合作育幼行为呈现独立演化关系，这表明鲜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，本研究还发现，虹膜色彩与筑巢行为的演化确实存在依存关系，但与预期相悖的是，树洞筑巢物种向色彩虹膜演化的频率并未高于非树洞筑巢物种。与之相反，研究结果表明，非树洞筑巢物种面临的抑制鲜亮眼部色彩的选择压力远强于树洞筑巢物种，这或许是因为未在树洞隐蔽的物种，其醒目的眼部色彩更容易被捕食者发现。