Colour vision, based on four spectrally distinct classes of cone photoreceptor, arose early in vertebrate evolution (500 MYA) and many present-day species retain tetrachromatic colour vision. However, colour vision has adapted to different photic environments by spectrally tuning the sensitivity of the cones and/or by varying the number of spectral cone classes. Mutations within an opsin gene can lead to a spectral shift in the sensitivity of the cone pigment, and a species may modify the ancestral pattern either by the loss of one or more of the four cone classes or by gene duplication. Mutations in the duplicated genes may lead to two or more spectrally distinct pigments within the single cone class. We are interested in the evolution of visual pigments and colour vision (colour perception), visual ecology (biology), and the structural and functional aspects of visual pigments, focusing on the molecular genetics (genes) underlying the mechanisms responsible for spectral tuning.