KIMBALL, R.T.*; MARKS, B.D.; HAN, K.-L.; University of Florida; Louisiana State University; University of Maryland: Relationship between evolution of the visual pigment rhodopsin and transitions to a nocturnal lifestyle in birds

Similar adaptations may sometimes arise independently in response to similar ecological conditions. Such convergence has been observed in visual pigments (opsins) in a variety of vertebrate lineages such as fish, birds, and mammals. The opsins form a gene family of visual pigments, of which there are five different opsins in birds. Rhodopsin, found in the rod cells, is responsible for day/night vision while the other four visual pigments are responsible for color vision. We collected rhodopsin sequences from a wide range of avian orders (including paleognathes and a diversity of neognathe orders) to get multiple independent comparisons of nocturnal and diurnal species. Absorbance of opsins can be estimated from amino acid sequences, allowing us to compare absorbance of rhodopsin between diurnal and nocturnal species. We also looked for specific amino acid substitutions in key sites, such as near the retinal-binding pocket between the diurnal and nocturnal species. We also examined rates of nonsynonymous to synonymous substitutions to determine whether there had been positive selection in nocturnal relative to diurnal taxa. Using these results, we determined whether avian rhodopsin sequences exhibit convergent evolution in response to a transition to a nocturnal lifestyle.