The molecular genetics and evolution of red and green color vision in vertebrates

To better understand the evolution of red-green color vision in vertebrates, we inferred the amino acid sequences of the ancestral pigments of 11 selected visual pigments: the LWS pigments of cave fish (Astyanax fasciatus), frog (Xenopus chicken (Gallus gallus), chameleon (Anolis carolinensis), goat (Capra hircus), and human (Homo sapiens); and the MWS pigments of cave fish, gecko (Gekko gekko), mouse (Mus musculus), squirrel (Sciurus carolinensis), and human. We constructed these ancestral pigments by introducing the necessary mutations into contemporary pigments and evaluated their absorption spectra using an in vitro LW assay. The results show that the common ancestor of vertebrates and most other ancestors had LWS pigments. Multiple regression analyses of ancestral and contemporary MINIS and LWS pigments show that single mutations S180A, II197Y, Y277F, T285A, A308S, and double mutations S18OA/H197Y shift the lambda (max) of the pigments by -7, -28, -8, -15, -27, and 11 nm, respectively. It is most likely that this "five-sites" rule is the molecular basis of spectral timing in the MWS and LWS pigments during vertebrate evolution.