The molecular evolution of avian ultraviolet- and violet-sensitive visual pigments.
The shortwave-sensitive SWS1 class of vertebrate visual pigments range in lambda(max) from the violet (385-445 nm) to the ultraviolet (UV) (365-355 nm), with UV-sensitivity almost certainly ancestral. In birds, however, the UV-sensitive pigments present in a number of species have evolved secondarily from an avian violet-sensitive (VS) pigment. All avian VS pigments expressed in vitro to date encode Ser86 whereas Phe86 is present in all non-avian ultraviolet sensitive (UVS) pigments. In this paper, we show by site directed mutagenesis of avian VS pigments that Ser86 is required in an avian VS pigment to maintain violet-sensitivity and therefore underlies the evolution of avian VS pigments. The major mechanism for the evolution of avian UVS pigments from an ancestral avian VS pigment is undoubtedly a Ser90Cys substitution. However, Phe86, as found in the Blue-crowned trogon, will also short-wave shift the pigeon VS pigment into the UV whereas Ala86 and Cys86 which are also found in natural avian pigments do not generate short-wave shifts when substituted into the pigeon pigment. From available data on avian SWS1 pigments, it would appear that UVS pigments have evolved on at least 5 separate occasions and utilize 2 different mechanisms for the short-wave shift.
Carvalho
Livia S
LS
UCL Institute of Ophthalmology, London, UK.
Cowing
Jill A
JA
Wilkie
Susan E
SE
Bowmaker
James K
JK
Hunt
David M
DM
D019943:Amino Acid Substitution; D000818:Animals; D001717:Birds / Q000235:genetics*; D003116:Color; D003118:Color Perception; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D010802:Phylogeny; D012168:Retinal Pigments / Q000235:genetics* / Q000378:metabolism; D017299:Rod Opsins / Q000737:chemistry*; D014466:Ultraviolet Rays
D018076:DNA, Complementary; D012168:Retinal Pigments; D017299:Rod Opsins