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，强烈的选择压力作用于动物的色彩特征。尽管诸多动物的虹膜颜色存在变异，但目前几乎未有研究探讨这类颜色特征的功能意义。雀形目（Passeriformes）鸟类的虹膜颜色丰富多样，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），检验了如下假说：雀形目鸟类显眼的虹膜颜色演化，一是为响应育幼协作的协调需求，二是与洞巢栖息习性相关——这两类特征均被认为与种内视线感知敏感性有关。研究发现，虹膜颜色与双/多个体协同育幼这两个性状的演化相互独立，这表明鲜亮的虹膜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筑巢行为的演化确实存在依存关系，但与理论预期相悖的是，洞巢鸟类向有色虹膜演化的频率并未高于非洞巢鸟类。与之相反，研究结果表明，非洞巢鸟类所承受的“规避鲜亮虹膜”的选择压力远强于洞巢鸟类，这可能是因为未在洞穴中隐蔽的物种，其显眼的虹膜颜色更容易被捕食者察觉。