Protective Coloration and Form
Protective Coloration and Form
in animals, coloration and form that promote preservation of life in the struggle for existence. Protective coloration is found among many groups of invertebrates and vertebrates. There are three types: camouflage, aposematism, and mimicry (seeMIMICRY).
Camouflage enables an animal to blend into the background of its surrounding, thereby making it easier to hide from predators. (Almost all animals marked by camouflage are able to hide.) Camouflage may be cyrptic, concealing, or disruptive. Cryptic coloration imitates the background in color and design. For example, insects that inhabit grass or live among the leaves of trees usually have a green coloration (grasshoppers, true bugs, caterpillars of butterflies and sawflies). Animals living in polar regions are white (willow ptarmigan, polar bear, arctic fox), and desert dwellers are yellow or brown (Phrynocephalus mystaceus, monitor, desert locust). Some animals (cuttlefish, octopuses, some fishes, chameleons) are capable of changing their coloration to blend with the background. This may be explained by the presence in their skin of cells having various pigments, which expand or contract upon receiving impulses from the central nervous system. The impulses originate from the sense organs, mainly the eyes.
Concealing coloration is based on countershading. The more brightly illuminated parts of the body are darker than parts subjected to less light.
The coloration seems monotone, and the outlines of the animal’s body blend with the background. Such coloration is widespread among aquatic animals (Notonectidae, squid, fishes, dolphins) and is sometimes observed in terrestrials (snakes, lizards, deer, hares, and the caterpillars of some butterflies).
Disruptive coloration is the presence of contrasting stripes or spots, which divide the body into separate areas and renders the animal unrecognizable against the background. Disruptive coloration, which is often combined with cryptic coloration, characterizes many animals, including the giraffe, the zebra, the Asiatic chipmunk, some fishes, various amphibians, some snakes, grasshoppers, and many butterflies and their caterpillars.
An animal with aposematic coloration stands out against its background. The combination of bright coloring with various protective adaptations has acquired the name “warning coloration.” Aposematism is characteristic of some poisonous snakes, salamanders, inedible fishes, ladybugs, blister beetles, bees, and wasps. It sometimes is not associated with inedibility or poisonousness and, in such cases, is usually combined with cryptic coloration. This is sometimes called deimantic behavior—a startle display in the event of danger. Examples of deimantic coloration are the bright red mouth folds of Phrynocephalus mystaceus, the eyespots of hawkmoths, and the bright bands and spots of the moth Catacola hupta and some grasshoppers. The coloration is usually combined with threatening posture, movement, or frightening sounds.
Protective coloration and form arose in animals in the process of evolution under the influence of natural selection. Their adaptive character is relative, since they lose their protective significance with changes in the environment.
REFERENCESCott, H. Prisposobitel’naia okraska zhivotnykh. Moscow, 1950. (Translated from English.)
Sheppard, P. M. Estestvennyi otbor i nasledstvennost’. Moscow, 1970. (Translated from English.)
I. K. SHAROVA