Coat color

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In its natural environment, the dikdik is almost invisible.

The color of the fur fulfills several functions in wild animals. It serves as a camouflage for both the predator and the prey. The adaptation of the coloration of the animals to the environment is a decisive natural selection criterion in the context of evolution .

The color of the fur is also used for communication . In rabbits and hares, as well as some ungulates, the white color underneath becomes visible as a warning signal when the tail is raised. In roe deer and fallow deer, this white fur area is called a mirror . The black and white fur pattern of the skunk serves as a warning color . Most mammals see fewer colors than humans because they only have two types of color cells, so contrasts and patterns are likely to be more important to them than color itself.

In contrast, birds with four types of cones have more differentiated color vision than humans. In chaffinches , the red color of the breast triggers courtship or aggression behavior . Mimicry is a concept in which a warning color is imitated by harmless animals, making them appear defensible.

Mythology of coat color

Cebus in different colors

It is not known when the first appearance of fur colors deviating from the wild form in domestic animals . It can be assumed that the colors of the fur were one of the first selection criteria for the domesticated animals.

Colored animals already play a decisive role in early historical mythologies . In the Bäarmagus saga, red animals like the fox or red cats give protection from lightning and fire or attract it. Red-haired people were often blamed for the sterility of the field. Redeemed or atone for souls take on white animal form. White animals were considered to be carriers of magical powers and happiness.

The fact that coat color was recognized as a hereditary trait is already documented in the Bible. In ( 1 Mos 30  EU ) of the Old Testament it is described how Jacob obtained speckled offspring from the mating of white sheep or black goats, which because of their coloration become his property.

Early references to the appearance of pets can be found in art. Ancient Egyptian works around 1500 BC Show brown, black, white and piebald horses. Up until the Middle Ages, pigs in pictures were very similar in shape and color to wild boars.

Development of coat color

History of color genetics

Different colored guinea pigs

The mode of inheritance of the coat colors was examined with the help of cross-breeding experiments and the colorations were assigned to specific gene locations . The laboratory mouse was examined most thoroughly and therefore represented the model for other animal species. By comparing the dominance relationships of the genes with each other, the effect of the alleles on the appearance and accompanying diseases in several animal species, SEARLE (1968) designed the cross-species allele series. In the species-specific allele series, on the other hand, alleles and gene locations are classified which can only be found in one or a few animal species. Later, the exact biochemical and molecular genetic background was gradually researched. It turned out that the same appearance can be based on different genotypes .

Migration and maturation of the pigment cell

Pied Syrian Hamster

Like the nerve , ganglia , glial , adrenal medulla and Schwann cells , the melanoblasts originate from the neural crest . They migrate into the epidermis during fetal development . There they mature from egg-shaped to star-shaped to dendritic cells. The melanin formation begins in the period of birth and is sometimes not completed until after birth. If this migration of the cells is disturbed, leucism or various piebalds develop . In contrast to the albino, there are no melanocytes in the white areas .

Pigment formation

Only the melanins that are formed in the pigment cells ( melanocytes ) are important for the development of coat colors . There are two forms of melanin , the black-brown eumelanin and the red-yellow pheomelanin . Both are synthesized from the essential amino acid tyrosine via the intermediate stages 3,4-dihydroxyphenylalanine (DOPA) and dopachinone .

Melanin formation can be influenced or disturbed at each of these intermediate stages by different alleles of the genes of melanin synthesis.

This includes mutations of the following gene locations

  • Siamese drawing in the rat

  • Brown cat

  • Brauner with cream gene

  • Arctic Wolf : extremely lightened pheomelanin

Genes that control pigment distribution

For better camouflage and as a signal, there are various patterns of the fur in nature. This is achieved by having various genes turn melanin production on or off as needed. The melanocytes of a hair follicle start pigment production at different times so that all shades of color can arise. Likewise, intensive melanin deposition can take place in one part of the melanosome, while adjacent parts are hardly active. The melanocytes can switch from producing one pigment to another. As a result, the matrix cells contain various pigments.

Genes that control when the melanocytes switch from eumelanin to pheomelanin and vice versa are as follows:

Blacklings - that is, animals with melanism - usually result from mutating one of these loci.

Articles about patterns:

Influences of the hair structure

In addition to the regulatory processes that the pigment cells themselves control in their work, the thickness, length, internal structure and growth speed of the hair also influence the color of the coat.

The structure of the hair can be changed in such a way that the pigment granules are much more difficult to store or not at all. This traps more air into the hair, making the hair appear lighter to white. In the mouse, an allele of the Mo locus leads to a striped drawing of the animal in this way.

In wild rabbits and mice, thick skin reduces the formation of pheomelanin, and from a certain growth rate the melanocytes form pheomelanin instead of eumelanin. The faster division of the matrix cells means that fewer pigments are stored in the hair cortex.

Since long hair reflects light differently than short hair, there are often color differences between the winter and summer fur of an animal.

Thicker hairs appear darker because the reflective surface shrinks in proportion to the amount of pigment. Hair with a pronounced medulla (hair pulp), on the other hand, appears lighter because the opaque core enlarges the reflective surface.

Coat colors of individual animal species

There are special conventions for the designation of the coat colors for different animal species, see the articles:

For further animal groups, see there, see also literature

literature

About special groups of animals:

  • Krista Siebel: Analysis of genetic variants of loci for coat color and their relationship to color phenotype and quantitative performance characteristics in pigs. Inaugural Dissertation for the Degree of Doctor of Veterinary Medicine; Institute for Animal Science at the Humboldt University in Berlin, July 2001.

Individual evidence

  1. ↑ Sheila Schmutz: K Locus