Evolution of songbird eggs colour

To understand why avian eggs are so variable in colour and patterning, we investigated contemporary species that provide insights into the evolutionary transitions that occurred during the early radiation of the songbirds. We quantified egg colour and patterning from museum collections of 269 species of Australian passerine and collated it to nest type data (cup or dome nesting species). Using phylogenetically reconstructed trait data, we showed that the ancestral passerine egg was likely to be white, and to have been laid inside a domed nest. Egg colouration and nest type were both phylogenetically clustered, and there was evidence of correlated evolution between the two traits. As nests transitioned from domes to cups, there was an increase in the range of egg colours observed, presumably as a response to additional stressors. Finally, we found that egg colour changes occurred more than twice as frequently in cup nesting species than in dome nesting species. This suggests that cup-nesting species may be using colour as an adaptive trait to compensate for the loss of the protective nest roof.

为探究鸟类蛋壳颜色和图案的多样性原因，本研究对现代物种进行了调查，以期揭示鸣禽早期辐射过程中的进化转变。通过对博物馆中269种澳大利亚鸣禽蛋壳颜色和图案的量化分析，并与巢穴类型数据（杯状或穹顶状筑巢物种）进行比对，我们运用系统发育重建的性状数据表明，祖先鸣禽的蛋壳可能是白色的，且产蛋于穹顶状巢穴之中。蛋壳颜色和巢穴类型在系统发育上均呈现集群分布，且两种性状之间存在着协同进化的证据。随着巢穴从穹顶状转变为杯状，观测到的蛋壳颜色范围有所增加，这可能是对额外压力源的适应性反应。最终，我们发现杯状巢穴物种中蛋壳颜色的变化频率是穹顶状巢穴物种的两倍以上。这一发现暗示，杯状巢穴物种可能利用颜色作为适应性特征，以补偿失去的巢穴屋顶保护作用。