Abstract
Owls (Strigiformes) represent a fascinating group of birds that are the ecological night-time counterparts to diurnal raptors (Accipitriformes). The nocturnality of owls, unusual within birds, has favored an exceptional visual system that is highly tuned for hunting at night, yet the molecular basis for this adaptation is lacking. Here, using a comparative evolutionary analysis of 120 vision genes obtained by retinal transcriptome sequencing, we found strong positive selection for low-light vision genes in owls, which contributes to their remarkable nocturnal vision. Not surprisingly, we detected gene loss of the violet/ultraviolet-sensitive opsin (SWS1) in all owls we studied, but two other color vision genes, the red-sensitive LWS and the blue-sensitive SWS2, were found to be under strong positive selection, which may be linked to the spectral tunings of these genes toward maximizing photon absorption in crepuscular conditions. We also detected the only other positively selected genes associated with motion detection in falcons and positively selected genes associated with bright-light vision and eye protection in other diurnal raptors (Accipitriformes). Our results suggest the adaptive evolution of vision genes reflect differentiated activity time and distinct hunting behaviors.
Highlights
Laboratory for Tropical Animal and Plant Ecology, College of Life Sciences, Hainan Normal University, Haikou 571158, www.nature.com/scientificreports/
Among 119 vision genes examined in owls, we found 9 genes to be under positive selection, including 5 dim-light vision genes (PDE6B, CNGB1, CNGA1, SAG and SLC24A1) involved in the phototransduction pathway in rods (Fig. 2)
The positive selection observed in five dim-light vision genes involved in the activation and recovery of photoresponse may help to enhance the sensitivity to light and possibly contribute to high visual acuity and high temporal resolution of vision in dim light conditions
Summary
Laboratory for Tropical Animal and Plant Ecology, College of Life Sciences, Hainan Normal University, Haikou 571158, www.nature.com/scientificreports/. The restoration of cGMP concentration incorporated with an efficient inactivation of each of the activated components involved in the phototransduction cascade is considered to be important for photoresponse recovery[8]. We performed a comparative evolutionary analysis of vision genes of 15 species of owls and close relatives within Afroaves (Coraciimorphae and Accipitriformes) and its sister clade, Australaves (Falconiformes) (Fig. 1) using retinal transcriptome sequencing to understand the molecular basis of the vision system in these groups. The assembled unigenes were highly reliable with an averaged sequence identity of 99.6% compared with the sequences obtained by clonal sequencing of one selected gene (RH1) (Supplementary Table 2). We assessed adaptive evolution across a total of 120 vision genes (Supplementary Tables 3 and 4) from the 26 species. A convergent or parallel molecular evolution of vision genes in owls and falcons was inferred
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