Evolution of color vision

Color vision, a proximate adaptation of the vision sensory modality, allows for the discrimination of light based on its wavelength components.

Invertebrates

Color vision requires a number of opsin molecules with different absorbance peaks, and at least three opsins were present in the ancestor of chelicerates and pancrustaceans; members of both these groups today possess color vision.^[1]

Vertebrates

Researchers studying the opsin genes responsible for color-vision pigments have long known that there exist four photopigment opsins in birds, reptiles and teleost fish.^[2] This indicates that the common ancestor of tetrapods and amniotes (~360 million years ago) had tetrachromatic vision—the ability to discern four different wavelengths of light—and thus at least this many (and probably far more) visual "colors."^[3] Thus, for example, the wide variety of colors and shades exhibited in fish on a coral reef needs no explanation in terms of color vision—such shallow-water fish see colors as well or better than humans do, and always have.

Today, most mammals possess dichromatic vision, corresponding to red–green color blindness. They can thus distinguish between violet, blue, green and yellow, but cannot distinguish reds and oranges. This was probably a feature of the first mammalian ancestors, which were likely small, nocturnal, and burrowing. At the time of the Cretaceous–Tertiary extinction event 65.5 million years ago, the burrowing ability probably helped mammals survive extinction. Mammalian species of the time had already started to differentiate, but were still generally small, comparable in size to rats; this small size would have helped them to find shelter in protected environments. In addition, it is postulated that some early monotremes, marsupials, and placentals were semiaquatic or burrowing, as there are multiple mammalian lineages with such habits today. Any burrowing or semiaquatic mammal would have had additional protection from K–T boundary environmental stresses.^[4] However, many such species evidently possessed poor color vision in comparison with non-mammalian vertebrate species of the time, including reptiles, birds, and amphibians.

Since the beginning of the Tertiary Period, surviving mammals enlarged, moving away by adaptive radiation from a burrowing existence and into the open, although most species kept their relatively poor color vision. Exceptions occur for some marsupials (which possibly kept their original color vision) and some primates—including humans. Primates, as an order of mammals, began to emerge around the beginning of the Tertiary Period. They have re-developed trichromatic color vision since that time, by the mechanism of gene duplication, being under unusually high evolutionary pressure to develop color vision better than the mammalian standard. Ability to perceive red^[5] and orange hues allows tree-dwelling primates to discern them from violet. This is particularly important for primates in the detecton of red and orange fruit, as well as nutrient-rich new foliage, in which the red and orange carotenoids have not yet been masked by chlorophyll.

Today, among simians, the catarrhines (Old World monkeys and apes, including humans) are routinely trichromatic—meaning that both males and females possess three opsins, sensitive to short-wave, medium-wave, and long-wave light^[3]—while, conversely, only a small fraction of platyrrhine primates (New World monkeys) are trichromats.^[6]

See also

• Evolution of color vision in primates
• Evolution of the eye

References

1. ^ Koyanagi, M.; Nagata, T.; Katoh, K.; Yamashita, S.; Tokunaga, F. (2008). "Molecular Evolution of Arthropod Color Vision Deduced from Multiple Opsin Genes of Jumping Spiders". Journal of Molecular Evolution 66 (2): 130. doi:10.1007/s00239-008-9065-9. PMID 18217181.  edit
2. ^ Yokoyama, S., and B. F. Radlwimmer. 2001. The molecular genetics and evolution of red and green color vision in vertebrates. Genetics Society of America. 158: 1697-1710.
3. ^ ^{a b} Bowmaker, JK (1998). "Evolution of colour vision in vertebrates". Eye (London, England) 12 ( Pt 3b): 541–7. PMID 9775215.  edit
4. ^ Robertson DS, McKenna MC, Toon OB, Hope S, Lillegraven JA (2004). "Survival in the first hours of the Cenozoic" (PDF). GSA Bulletin 116 (5–6): 760–768. doi:10.1130/B25402.1. http://www.ugcs.caltech.edu/~presto/cenozoic.pdf. Retrieved 2007-08-31. 
5. ^ Dulai, KS; von Dornum, M; Mollon, JD; Hunt, DM (1999). "The evolution of trichromatic color vision by opsin gene duplication in New World and Old World primates". Genome research 9 (7): 629–38. PMID 10413401.  edit
6. ^ Surridge, A. K., and D. Osorio. 2003. Evolution and selection of trichromatic vision in primates. Trends in Ecol. and Evol. 18: 198-205.