Retinal transcriptome analysis of four owl species: Longeared owl (Asio otus), Short-eared owl (Asio flammeus), Tawny owl (Strix aluco) and Boreal owl (Aegolius funereus)

Owls (Strigiformes) are birds that typically have crepuscular or nocturnal activity patterns. Even though birds are known to have an exceptional visual system, less is known about specific adaptations to vision in dim conditions. Here, by using retinal transcriptome sequencing, the visual gene pathway has been analyzed in four owl species: Long-eared owl (Asio otus), Short-eared owl (Asio flammeus), Tawny owl (Strix aluco) and Boreal owl (Aegolius funereus). Most birds studied to date have the four cone opsin pigments LWS, RH2, SWS2 and SWS1. For the examined owl species the ultraviolet-/violet-sensitive opsin (SWS1) could not be found in any of the species, the greensensitive opsin (RH2) had a low expression. In addition to this, positively selected sites was found in genes involved in dim light vision as well as a high expression of phototransduction-activating genes in A. flammeus and A. funereus. The results conform with previous findings of positively selected sites in vision genes as well as loss of the SWS1 gene in owls, which suggest adaptation of the retinal genes to crepuscular and nocturnal activity patterns.