Comparative genomics of adaptation to nocturnal lifestyle in owls

Though the majority of birds is diurnal, nocturnality has evolved independently in parrots, kiwis, oilbirds, nightjars and owls. Owls share traits with other raptors and nocturnal birds, such as cryptic plumage patterns, reversed sexual size dimorphism and acute vision and hearing. Additionally, some traits are owl specific, such as their asymmetrical ears, dish-shaped faces, and silent flying due to their feather's structure. The genetic basis of some of these adaptations to a nocturnal predatory lifestyle has been studied by candidate gene approaches, but rarely with genome-wide scans. Here, we used a genome-wide comparative analysis to test for selection in the early history of the Strigiformes. We estimated the substitution rates in the coding regions of twenty bird genomes, including eleven owl species of which five were newly sequenced. Then, we tested for functional overrepresentation across the genes with selection signals. In the ancestral branch of the owls, we found that positive selection has led the evolution of genes functionally related to visual perception, especially to phototransduction, and chromosome packaging. Other genes with selection signals were functionally related to acoustic perception, circadian rhythm and feathers. We discuss whether these results support previous findings and how selection could affect the early adaptative history of the Strigiformes as nocturnal birds of prey.