Molecular evolution of color vision of zebra finch

Abstract

We have isolated and sequenced the RH1Tg, RH2Tg, SWS2Tg, and LWSTg opsin cDNAs from zebra finch retinas. Upon binding to 11-cis-retinal, these opsins regenerate the corresponding photosensitive molecules, visual pigments. The absorption spectra of visual pigments have a broad bell shape, with the peak being called λmax. Previously, SWS1Tg opsin cDNA was isolated from zebra finch retinal RNA, expressed in cultured COS1 cells, reconstituted with 11-cis-retinal, and the λmax of the resulting visual pigment was shown to be 359nm. Here, the λmax values of the RH1Tg, RH2Tg, SWS2Tg, and LWSTg pigments are determined to be 501, 505, 440, and 560nm, respectively. Molecular evolutionary analyses suggest that specific amino acid replacements in the SWS1 and SWS2 pigments, resulting from accelerated evolution, must have been responsible for their functional divergences among the avian pigments.