Molecular analysis of the evolutionary significance of ultraviolet vision in vertebrates

Many fish, amphibians, reptiles, birds, and some mammals use UV vision for such basic activities as foraging, mate selection, and communication. UV vision is mediated by UV pigments in the short wavelength-sensitive type 1 (SWS1) group that absorb light maximally (lambda(max)) at approximate to360 nm. Reconstructed SWS1 pigments of most vertebrate ancestors have lambda(max) values of -360 nm, whereas the ancestral avian pigment has a lambda(max) value of 393 nm. In the nonavian lineage, UV vision in many modern species is inherited directly from the vertebrate ancestor, whereas violet vision in others has evolved by different amino acid replacements at approximate to10 specific sites. In the avian lineage, the origin of the violet pigment and the subsequent restoration of UV pigments in some species are caused by amino acid replacements F49V/F86S/L116V/S118A and S90C, respectively. The use of UV vision is associated strongly with UV-dependent behaviors of organisms. When UV light is not available or is unimportant to organisms, the SWS1 gene can become nonfunctional, as exemplified by coelacanth and dolphin.