Tetrachromate

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A tetrachromacy ( ancient Greek τετρα- tetra "four" and χρῶμα chroma "color") is a living being that four types of color receptors to see used.

Basics

The person usually has in the photosensitive retina of the eye three different types of color-sensitive photoreceptors, the cones so, and as trichromate referred. The color sensitivity of the cones is based on the different absorption maxima of the respective visual pigments, consisting of S-, M- and L- opsin and the retinal chromophore . In the case of rods , on the other hand, there is only one visual pigment ( rhodopsin ), which is why they are insensitive to color.

Many animals have a fourth color receptor that is sensitive, for example, in the yellow or ultraviolet range of light. These animals are called tetrachromats. A fourth color receptor can enlarge the perceived color spectrum or improve the differentiation within the perceived spectrum, provided that this color perception is also processed by the brain.

Primary tetrachromasia

Color sensitivity of the cones in primary tetrachromasia

Many vertebrates (fish, amphibians, reptiles and birds), but also arthropods such as jumping spiders and insects are tetrachromates. For example, in addition to the red-, green- and blue-sensitive cones, the goldfish has a UV cone that can absorb very short-wave, ultraviolet light and process this information. Tetrachromasia is therefore likely to be a widespread property of the vertebrate eye . Even birds use the fourth color as by special UV reflectance patterns in the plumage.

Many higher mammals , however, are dichromates (with only two types of cones). The cause is believed to be that the ancestors were nocturnal and that this way of life was accompanied by the loss of two types of photopigments in the cones (for example that for UV). In the case of marsupials, there are indications that they only reduced one photopigment and are therefore probably primarily trichromats (incidentally, their retina shows other "reptilian properties"). In some Old World monkeys, and therefore ultimately in humans, the trichromatism developed secondarily through partial duplication of the gene on the X chromosome .

Secondary tetrachromasia in humans

The genes for L and M opsin are located on the X chromosome in humans . Since women have two X chromosomes, they can - especially if they have a deuteranomal or protanomal parent - an additional changed color receptor, the sensitivity of which is usually between that of the red and green receptors and which is therefore classified as yellow. or orange receptor is to be qualified. This four-color pigment genotype occurs in twelve percent of all women. However, the genotype rarely leads to tetrachromasia, since there is usually no separate neuronal processing of the signals of the fourth color receptor. However, individual cases of experimentally verified tetrachromatic, i.e. more differentiated, color perception have already been described.

Tetrachromatic views

The surface of many fruits reflects UV light. This makes it easier for animals with the ability to perceive UV light to find it. Certain species of falcon are tetrachromates, they discover the trail of their prey by means of their markings made of UV-reflective urine or excrement .

Individual evidence

  1. ^ W. Backhaus, R. Kliegl, JS Werner: Color vision: perspective from different disciplines. Walter de Gruyter, 1998, ISBN 3-11-015431-5 , pp. 163-182.
  2. ↑ a b Gerhard Neuweiler, Gerhard Heldmaier: Comparative animal physiology . tape 1 : Neuro- and Sensory Physiology . Springer, Berlin / Heidelberg 2003, ISBN 3-540-44283-9 , pp. 463-473 .
  3. ↑ M. Stevens (Ed.): Sensory Ecology, Behavior, and Evolution. Oxford 2013.
  4. ^ A. Kelber et al.: Animal color vision - behavioral tests and physiological concepts. In: Biological Reviews. 2007. doi: 10.1017 / S1464793102005985
  5. ↑ T. Okano, Y. Fukada, T. Yoshizawa: Molecular basis for tetrachromatic color vision. In: Comp Biochem Physiol B Biochem Mol Biol. 112 (3), Nov 1995, pp. 405-414. Review. PMID 8529019
  6. ^ KA Jameson, SM Highnote, LM Wasserman: Richer color experience in observers with multiple photopigment opsin genes. In: Psychon Bull Rev. 8 (2), Jun 2001, pp. 244-261. PMID 11495112
  7. ↑ Gabriele Jordan et al .: The dimensionality of color vision in carriers of anomalous trichromacy. In: Journal of Vision. 10, No. 8, 2010, pp. 1-19. doi : 10.1167 / 10.8.12