Chromatophore

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Chromatophore

A pigmented structure found in many animals, generally in the integument. The term is usually restricted to those structures that bring about changes in color or brightness. A majority of chromatophores are single cells that are highly branched and contain pigment granules that can disperse or aggregate within the cell. However, in coleoid cephalopod mollusks (all mollusks except Nautilus), the chromatophores function as miniature organs, and changes in the dispersion of pigment are brought about by muscles. Although the mode of action of the two types of chromatophore is completely different, the effect is the same: pigment either is spread out over a large area of the body or is retracted into a small area.

The movement of pigment takes place in many chromatophores simultaneously, so that the effect is a change in the quality of light reflected from the surface of the animal. The color change functions as a camouflage from predator or prey, but it may also serve for regulating temperature, protecting against harmful radiation, and in signaling. Light stimulates the responses of chromatophores, generally indirectly via the eyes and central nervous system.

Single-cell chromatophores are found in some annelids, insects, and echinoderms. They are much more conspicuous in crustaceans (shrimps and prawns), in fishes (especially in bony fish and teleosts), in anuran amphibians (frogs and toads), and in a few reptiles. The chromatophores may be uniformly distributed in the skin (chameleons), or they may occur in patches (flounders) or lines (around the abdomen in shrimps). Chromatophores of various colors may be distributed unevenly across the body, and occur at different depths in the skin.

Chromatophores produce their colors by reflection after absorption of light. Generally, the light comes from above, but it may come from below after reflection from an underlying structure. The most common type of chromatophore contains melanin (and is, therefore, often called a melanophore), which absorbs all wavelengths so that the chromatophore appears black; other types have red (erythrophores) or yellow (xanthophores) pigments. These pigments generally derive from carotenoids in vertebrates.

Chromatophores contain pigment granules that move within them, giving them an appearance that ranges from spotted to fibrous on the five-stage scale that is widely used to measure the degree of chromatophore expansion. If the pigment within the particular cell is black or brown, the integument takes on a dark appearance when most of the chromatophores are in the last stage of dispersion (stage 5). If the pigment color is yellow or cream, the animal tends to look paler if all the chromatophores are at that stage.

In crustaceans, elasmobranch fishes, anurans, and lizards, control of the chromatophores is thought to be exclusively hormonal. Such hormonal control is true also of some teleosts; in others the control is part hormonal and part neural; while in still others control is purely neural, as in the chameleon. Where nerves are involved, the speed of the response is faster, the chromatophores responding in minutes rather than hours. See Neurosecretion

Each cephalopod chromatophore organ comprises an elastic sac containing pigment granules. Attached to the sac is a set of 15–25 radial muscles that are striated and contract rapidly. Associated with the radial muscles are axons from nerve cell bodies that lie within the brain. Active nerve cells cause the radial muscles to contract and the chromatophore sac expands; when the nerves are inactive, energy stored in the elastic sac causes the chromatophore to retract as the muscles relax. The chromatophores receive only nerve impulses, and there is no evidence that they are influenced by hormones. The chromatophores are ultimately controlled by the optic lobe of the brain under the influence of the eyes.

Two consequences follow from the fact that cephalopod chromatophores are under the direct control of the brain. First, color change is instantaneous. Second, patterns can be generated in the skin in a way impossible in other animals. Thus, cephalopods can use the chromatophores not just to match the background in general color but to break up the body visually (disruptive coloration) so that a predator does not see the whole animal. Because the chromatophores are neurally controlled and patterns can be produced in the skin, they can also be used for signaling. See Pigmentation, Protective coloration

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Chromatophore

 

(1) In animals and humans, a pigment cell.

(2) In plants, an organelle of brown and green algae that may be filamentous (as in Spirogira) or stellate in form. Like the chloroplasts of higher plants, chromatophores are separated from the cytoplasm of the cell by a two-layered protein-lipid membrane. They contain chlorophylls, carotenoids, and other substances. Photosynthesis occurs in chromatophores.

(3) In microorganisms, an organelle of photosynthesizing bacteria, usually not separated from the cytoplasm by a membrane. Chromatophores contain bacteriochlorophylls, carotenoids, and a number of electron carriers, as well as enzymes that help synthesize pigments. Photosynthesis occurs in them.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

chromatophore

[krō′mad·ə‚fȯr]
(cell and molecular biology)
A type of pigment cell found in the integument and certain deeper tissues of lower animals that contains color granules capable of being dispersed and concentrated.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Research showed that iridophores change their shape in carefully orchestrated patterns on the skin of zebrafish, and the changes in shape instruct the other two types of cells on where to go in ways that result in stripes.
"In our mathematical model, we use what we know about the interactions of the other two cell types to explain what drives iridophore behavior.
Some are simple units made of melanophores and leucophores, or melanophores and iridophores, and the synergistic action of the chromatophores that form these simple units responding to neural changes is the basis of rapid color changes (Herring 1994, Fujii et al.
The simultaneous appearance of the white and silver coloration could be the product of both the dispersion of leucosomes (product of the same nervous stimuli that caused the aggregation of melanosomes) and the exposure of non-motile iridophores to incident light.
A pairwise comparison test showed that mean durations were significantly higher in the most enduring components, such as clear, iridophore splotches, and bands (P < 0.05), than in the most short-lived components: arm spots, lateral mantle spot in females, fin stripe, accentuated oviducal gland, lateral mantle streaks, and dark dorsal stripe (Fig.
This patterning leads to chromatic components such as the dorsal stripe, arm spots, and the iridophore splotches located on the mantle, fin, and head.
Studies of the physiological and morphological features of the bluish colorations of tropical fish have shown that the integumental bluish hues are generated by a multi-layered interference phenomenon of the "non-ideal" type in piles of extremely thin-film reflecting platelets formed inside the iridophores (9-13).
A few iridophores that displayed a small amount of reflected and scattered incident light were observed in the blue region under epi-illumination optics (data not shown).
Malleable skin coloration in cephalpods: selective reflectance, transmission and absorbance of light by chromatophores and iridophores. Cell Tissue Res.
Previous studies have never furnished evidence of innervated squid iridophores (4).
Dorsal mantle collar iridophores are on the anteriormost portion of the mantle, and they appear as bright yellow or pink iridescence; this component tends to produce disruptive coloration by breaking up the longitudinal aspect of the squid's body.
Two iridescent components, both thought to aid in crypsis, were also observed: Dorsal mantle collar iridophores and Dorsal mantle splotches; these are not illustrated but can be seen in color plates in Hanlon (1982).