Meeting Abstract
Vertebrate color vision has evolved through the modification of five ancestral visual opsin proteins via gene duplication, loss and shifts in spectral sensitivity. While many vertebrates, including mammals, birds and fishes, have had their visual opsin repertoires studied in great detail, crocodylians have largely been neglected. Of particular significance is a purported nocturnal bottleneck experienced by stem crocodylians, predicted on the basis of comparative eye anatomy. A long period of dim-light adaptation has also been hypothesized for mammals, undergirded by ocular anatomy and the loss of light-dependent genes. Here I examine the genomic basis for color vision in four species of crocodylians, and found that they experienced a reduction in their color discrimination capacity after their divergence from birds. Based on the opsin sequences present in their genomes and previous measurements of crocodylian cones, I provide evidence that crocodylians have co-opted the rod opsin (RH1) for cone function. This further implies that some crocodylians have reinvented trichromatic color vision in a novel way, analogous to several primate lineages. The loss of visual opsins is also associated with the loss of non-visual opsins and genes associated with protection from ultraviolet light, many of which were lost in parallel in mammals. Two genes, encoding parietopsin and parapinopsin, were additionally inactivated in birds and turtles, likely co-occurring with the loss of the parietal eye in these lineages.
