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.

学界已证实，强烈的选择压力会对动物的色彩特征施加选择作用。尽管诸多动物的眼色存在差异，但目前几乎未有研究探讨这类色彩特征的功能意义。雀形目（Passeriformes）鸟类的虹膜颜色存在多样变化，使其成为探究虹膜颜色演化路径与演化动因的理想研究体系。我们采用系统发育比较法（phylogenetic comparative methods），验证了如下假说：雀形目鸟类的醒目虹膜颜色演化，是为响应两项与种内视线感知敏感性相关的特征——（a）育幼行为协作，以及（b）洞巢栖息习性。研究结果显示，虹膜颜色与由两名及以上个体开展的合作育幼行为呈独立演化关系，这表明醒目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，我们发现虹膜颜色与筑巢行为的演化确实存在依赖关联，但与预期相悖的是，洞巢物种向有色虹膜演化的频率并未高于非洞巢物种。与之相反，我们的研究结果表明，非洞巢物种所承受的、规避醒目眼部色彩的选择压力远强于洞巢物种，这或许是因为未在洞穴中隐蔽栖息的物种，其醒目的眼部色彩更容易被天敌察觉。