Gene duplications and evolution of the short wavelength-sensitive visual pigments in vertebrates

Abstract

When invertebrate rhodopsins were used as the outgroup, the rooted phylogenetic tree of 26 vertebrate visual pigments (VPs) was constructed. These VPs are distinguished into the following four clusters: (1) RH1 cluster consisting of rhodopsins, (2) RH2 cluster consisting of VPs with variable ranges of absorption spectra, (3) SWS cluster of short wavelength-sensitive VPs, and (4) LWS/MWS cluster of long and medium wavelength-sensitive VPs. Short wavelength-sensitive VPs from Astyanax fasciatus (AF23), goldfish (B(Ca)), chicken (B(Gg) and V(Gg)), and human (B(Hs)) belong to SWS cluster, whereas that from gecko (B(Gge)) belongs to the RH2 cluster. The SWS cluster is further divided into SWS-I (B(Hs) and V(Gg)) and SWS-II (AF23, B(Ca), and B(Gg)) groups. The SWS-I group has accumulated more amino acid changes than any other group of VPs. It is suggested that amino acid changes at a few key positions might have been important in the functional differentiation of the SWS-I group from the SWS-II group.