Seeing Nemo: molecular evolution of ultraviolet visual opsins and spectral tuning of photoreceptors in anemonefishes (Amphiprioninae)

Many animals can see ultraviolet (UV) light (shorter than 400 nm) undetectable to human vision. UV vision may have functional importance in many taxa including for foraging and communication in birds, reptiles, insects and teleost fishes. Shallow coral reefs transmit a broad spectrum of light and are rich in UV; driving the evolution of diverse spectral sensitivities in teleost reef fishes, including UV-sensitivity. However, the identities and sites of the specific visual genes that underly vision in reef fishes remain elusive and are useful in determining how molecular evolution has tuned vision to meet the ecological demands of life on the reef. We investigated the visual systems of eleven anemonefish (Amphiprioninae) species, specifically probing for the molecular pathways that facilitate UV-sensitivity. Searching the genomes of anemonefishes, we identified a total of seven functional visual genes from all five vertebrate opsin gene subfamilies. We found rare instances of UV-sensitive SWS1 opsin gene duplications, that produced two functional paralogs (SWS1 and SWS1{beta}) and a pseudogene. We also found separate RH2A opsin gene duplicates not yet reported in the family Pomacentridae. Finally, we report on both qualitative and quantitative aspects of opsin gene expression found in the adult retina of the false clown anemonefish (Amphiprion ocellaris), and their photoreceptor spectral sensitivities measured using microspectrophotometry.