Assessing the use of genomic DNA as a predictor of the maximum absorbance wavelength of avian SWS1 opsin visual pigments

Recently, in vitro mutation studies have made it possible to predict the wavelengths of maximum absorbance (lambda(max)) of avian UV/violet sensitive visual pigments (SWS1) from the identity of a few key amino acid residues in the opsin gene. Given that the absorbance spectrum of a cone's visual pigment and of its pigmented oil droplet can be predicted from just the lambda(max), it may become possible to predict the entire spectral sensitivity of a bird using genetic samples from live birds or museum specimens. However, whilst this concept is attractive, it must be validated to assess the reliability of the predictions of lambda(max) from opsin amino acid sequences. In this paper, we have obtained partial sequences covering three of the known spectral tuning sites in the SWS1 opsin and predicted lambda(max) of all bird species for which the spectral absorbance has been measured using microspectrophotometry. Our results validate the use of molecular data from genomic DNA to predict the gross differences in lambda(max) between the violet- and ultraviolet-sensitive subtypes of SWS1 opsin. Additionally, we demonstrate that a bird, the bobolink Dolichonyx oryzivorus L., can have more than one SWS1 visual pigment in its retina.