Potential of fish opsin gene duplications to evolve new adaptive functions.

The duplication of four cone-opsin gene families is heavily involved in visual adaptation in bony fish. We found that two gene families for the middle-wave range of the vision spectrum have, on average, older duplications followed by accelerated amino acid substitution, in comparison with the other two families that define the boundaries. This could be due to the difference in the potential to evolve new functions; middle-wave genes should have greater contribution to adaptive vision evolution through gene duplication.