Evolutionary dynamics of rhodopsin type 2 opsins in vertebrates

Among the five groups of visual pigments in vertebrates, the rhodopsin type 2 (RH2) group shows the largest number of gene duplication events. We have isolated three intact and one nonfunctional RH2 opsin genes each from Northern lampfish (Stenobrachius leucopsarus) and scabbardfish (Lepidopus fitchi). Using the deduced amino acid sequences of these and other representative RH2 opsin genes in vertebrates, we have estimated the divergence times and evolutionary rates of amino acid substitution at various stages of RH2 opsin evolution. The results show that the duplications of the lampfish and scabbardfish RH2 opsins have occurred approximately 60 and approximately 30 million years ago (Ma), respectively. The evolutionary rates of RH2 opsins in the early vertebrate ancestors were approximately 0.25 x 10(-9)/site/year, which increased to approximately 1 x 10(-9) to 3 x 10(-9)/site/year in euteleost lineages and to approximately 0.3 x 10(-9) to 0.5 x 10(-9)/site/year in coelacanth and tetrapods.