Title: Evolution of colour vision Content: The evolution of colour vision causes light to be seen according to its wavelength. This has obvious advantages, especially it helps animals find food. The colour vision of many herbivores allows them to see fruit or (immature) leaves which are good to eat. In hummingbirds, particular flowers are often recognized by colour. Predators also use colour vision to help them find their prey. All this applies mainly to animals in the daytime. On the other hand, nocturnal mammals have much less-developed colour vision. For them, space on the retina is better used with more rods since rods collect light better. Colour differences are much less visible in the dark. ==Arthropods== Apart from vertebrates,Lamb T.D; Collin S.P. & Pugh E.N. Jr. 2007. Evolution of the vertebrate eye: opsins, photoreceptors, retina and eye cup. Nature Reviews Neuroscience. 8 (12): 960–976. the only land animals to have colour vision are arthropods. Aquatic arthropods such as crustacea also have colour vision. As with vertebrates, the details differ, but the molecules which do the work the opsins – are very similar. ==Vertebrates== Four photopigment opsins exist in teleost fish, reptiles and birds.Yokoyama S. & Radlwimmer B.F. 2001. The molecular genetics and evolution of red and green color vision in vertebrates. Genetics Society of America. 158: 1697-1710. This suggests that the common ancestor of tetrapods and amniotes (~360 million years ago) had full colour vision: :"rods and four spectral classes of cone each [have] one of the five visual pigment families. The complement of four spectrally distinct cone classes gives these species the potential for tetrachromatic colour vision".Bowmaker J.K. 1998. Evolution of colour vision in vertebrates. Eye 12 (3b): 541–547. (Prose slightly simplified)Jacobs G.H. 2009. The evolution of colour vision in mammals. Phil Trans Roy Soc B. 364 (1531) 2957-2967. ===Mammals=== In contrast, mammals lost much of their colour vision capability during the long period in the Mesozoic when they lived as nocturnal animals.Kemp T.S. 2005. The origin and evolution of mammals. Oxford University Press. :"...two cone opsin gene families appear in contemporary eutherian mammals and, with the exception of some primates, none of these animals derive more than a single photopigment type from each of their two gene families". Many primates do live as daytime animals, and one group – the Old World monkeys – has trichromatic vision.There was gene duplication of one of their opsin genes. The anthropoid apes and humans are descended from this group of monkeys,The group is called the catarrhines. and also have good colour vision. So it comes about that most monkeys and humans have good colour vision, but most other eutherian mammals do not: they have only two opsins, and so they are bichromatic.Evolution of colour vision in vertebrates. Eye 12 (3b): 541–547. This has many consequences. For example, most deer cannot see red or orange. Thus they do not see the orange colour of tigers. But monkeys do, because primates have one more opsin than other mammals. A film by David Attenborough illustrates this well.BBC: Attenborough's life in colour: 1.2 Hiding in colour. ==UV light== Ultraviolet light plays a part in colour perception in many animals, especially insects. Colour vision, with UV discrimination, is present in many arthropods—the only terrestrial animals besides the vertebrates to have this trait.Koyanagi M. et al 2008. Molecular evolution of arthropod color vision deduced from multiple opsin genes of jumping spiders. Journal of Molecular Evolution 66 (2): 130–137. Birds, turtles, lizards, many fish and some rodents have UV receptors in their retinas. These animals can see the UV patterns found on flowers and other wildlife that are invisible to the human eye.