The molecular basis for spectral tuning of rod visual pigments in deep-sea fish

Most species of deep-sea fish possess of a rod-only retina with a pigment that is generally shortwave shifted in lambda(max) towards the blue region of the spectrum. In addition, the lambda(max) values of different species tend to cluster at particular points in the spectrum. In this study, the rod opsin gene sequences from 28 deep-sea fish species drawn from seven different Orders are compared. The lambda(max) values of the rod pigments vary from approximately 520 nm to <470 nm, with the majority lying between 490 nm and 477 nm. The 520 nm pigment in two species of dragon fish is associated with a Phe261Tyr substitution, whereas the shortwave shifts of the pigments in the other 26 species are accountable by substitutions at a further eight sites (83, 122, 124, 132, 208, 292, 299 and 300). Clustering of lambda(max) values does not, however, involve a common subset of these substitutions in the different species. A phylogenetic analysis predicts that the pigment in the ancestral species would have had a lambda(max) of approximately 480 nm. A total of 27 changes is required to generate the pattern of substitutions seen in the different species, with many sites undergoing multiple changes.