MBE Advance Access originally published online on June 7, 2007
Molecular Biology and Evolution 2007 24(8):1843-1852; doi:10.1093/molbev/msm109
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Research Articles |
The Molecular Evolution of Avian Ultraviolet- and Violet-Sensitive Visual Pigments
UCL Institute of Ophthalmology, London, EC1V 9EL, United Kingdom
E-mail: d.hunt{at}ucl.ac.uk
Accepted for publication May 21, 2007.
The shortwave-sensitive SWS1 class of vertebrate visual pigments range in 
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.
Key Words: visual pigments • ultraviolet • spectral tuning • birds • vision
Adriana Briscoe, Associate Editor