Vorobyev M, 2006, "Evolution of colour vision: The story of lost visual pigments" Perception 35 ECVP Abstract Supplement
Evolution of colour vision: The story of lost visual pigments
Colour vision appeared early in the evolution of vertebrates. Lampreys, the closest living relatives of the first vertebrates, have four types of cone visual pigments. These pigments were retained in many species of teleost fish, in diurnal reptiles, and birds. However, one or more cone pigments were lost in some fish species, in amphibians, geckos, crocodiles, and mammals, presumably when ancestors of these animals lived in dim light conditions. The loss of cone visual pigments in dim light could be explained in two different ways: (1) cone pigments were lost, because, in dim light, colour vision was not used; (2) in dim light, the reduction of the number of cone types improved colour vision. To test which of these is correct, I estimated the upper limit for the number of colours that can be discriminated by visual systems with different number of spectral types of cones. Discrimination threshold was set by the fluctuations in the number of absorbed quanta. Calculations show that in dim light the loss of a cone type may result in an increase of the number of colours that can be discriminated, eg in dim light dichromatic mammals may discriminate more colours then tetrachromatic birds.
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