The 'five-sites' rule and the evolution of red and green color vision in mammals

Abstract

Amino acid changes S180A (S → A at site 180), H197Y, Y277F, T285A, and A308S are known to shift the maximum wavelength of absorption (λmax) of red and green visual pigments toward blue, essentially in an additive fashion. To test the generality of this 'five-sites' rule, we have determined the partial amino acid sequences of red and green pigments from five mammalian orders (Artiodactyla, Carnivora, Lagomorpha, Perissodactyla, and Rodentia). The result suggests that cat (Fells catus), dog (Canis familiaris), and goat (Capra hircus) pigments all with AHYTA at the five critical sites have λmax values of ~530 nm, whereas rat (Rattus norvegicus) pigment with AYYTS has a λmax value of ~510 nm, which is accurately predicted by the five-sites rule. However, the observed λmax values of the orthologous pigments of European rabbit (Oryctolagus cuniculus), white-tailed deer (Odocoileus virginianus), gray squirrel (Sciurus carolinensis), and guinea pig (Cavia procellus) are consistently more than 10 nm higher than the predicted values, suggesting the existence of additional molecular mechanisms for red and green color vision. The inferred amino acid sequences of ancestral organisms suggest that the extant mammalian red and green pigments appear to have evolved from a single ancestral green-red hybrid pigment by directed amino acid substitutions.