MIMICRY

in biology, phenomenon characterized by the superficial resemblance of two or more organisms that are not closely related taxonomically. This resemblance confers an advantagesuch as protection from predationupon one or both organisms through some form of information flow that passes between the organisms and the animate agent of selection. The agent of selection (which may be, for example, a predator, a symbiont, or the host of a parasite, depending on the type of mimicry encountered) interacts directly with the similar organisms and is deceived by their similarity. This type of natural selection distinguishes mimicry from other types of convergent resemblance that result from the action of other forces of natural selection (e.g., temperature, food habits) on unrelated organisms. In the most studied mimetic relationships the advantage is one-sided, one species (the mimic) gaining advantage from a resemblance to the other (the model). Since the discovery of mimicry in butterflies in the mid-19th century, a great many plants and animals have been found to be mimetic. In many cases the organisms involved belong to the same class, order, or even family, but numerous instances are known of plants mimicking animals and vice versa. Although the best-known examples of mimicry involve similarity of appearance, investigations have disclosed fascinating cases in which the resemblance involves sound, smell, behaviour, and even biochemistry. A key element in virtually every mimetic situation is deception by the mimic, perpetrated upon a third party, which mistakes the mimic for the model. This third party may be the collective potential predators upon the mimic, potential prey of a predacious mimic, or even one sex of the mimic's own species. In some cases, such as host mimicry by parasites, the organism deceived is the model. Because of the variety of situations in which mimicry occurs, a formal definition must rest upon the effect of certain key communicative signals upon the appropriate receiver and the resultant evolutionary effect upon the emitters of the signals. Mimicry may be defined as a situation in which virtually identical signals, emitted by two different organisms, have in common at least one receiver that reacts in the same manner to both signals because it is advantageous to react in that manner to one of them (that of the model), although it may be disadvantageous to react thus to the counterfeit signal. The distinction between camouflage and mimicry is not always clear when only the model and the mimic are at hand. When the receiver is known and its reactions understood, however, the distinction is quite clear: in mimicry the signals have a special significance for the receiver and for the sender, which has evolved the signals in order to be perceived by the receiver; in camouflage the sender seeks to avoid detection by the receiver through imitation of what is neutral background to the receiver. For information on camouflage, see coloration: Camouflage. in biology, form of resemblance between two or more organisms that has evolved through the survival advantage conferred upon one or more of the organisms by means of some information flow between these organisms and an animate agent of selection. In 1862 the English naturalist H.W. Bates developed the theory of mimicry to explain the similar appearances of two unrelated species of butterflies. Bates observed that one species, marked by a distinctive coloration, was noxious and inedible by birds and thus served as the model for another species that was edible. The palatable species mimicked the markings of the inedible one, sending a deceptive signal to birds. The principle of Batesian mimicry is that one organism, lacking defenses against a predator, engages in mimicry to take advantage of the defenses of the model. Bates also observed, however, that a group of butterfly species, all of which were inedible, were similar in appearance. He could not explain why such should be the case, since each of the species in question had an adequate defense to back up its warning coloration. In 1878 Fritz Mller, a German zoologist, offered an explanation for this apparent paradox. According to his line of reasoning, the resemblance between the distasteful or formidable species themselves was an adaptation that economizes life; i.e., if two inedible species are alike, they will share between them the lives collectively lost before the predators have learned to associate the warning characteristics with their special means of defense. If they are dissimilar in appearance, the lives must be contributed by each species independently. Resemblances of this typea form of common or combined warningare termed Mllerian mimicry. Batesian and Mllerian mimicry are essentially defensive responses made by species against their predators. There also are cases in which a predator engages in mimicry to overcome its prey. An example of aggressive mimicry occurs with the sabre-toothed blenny (Aspidontus taeniatus), a fish that occurs with the cleaner wrasse (Labroides dimidiatus). The wrasse is marked with black and white stripes and executes a characteristic swimming movement, features that identify it to other fish, who then allow it to approach and eat parasites attached to their skin. The blenny resembles the cleaner fish both in markings and behaviour, permitting it to approach other fish, on which it then feeds. Another type of aggressive mimicry involves parasites who mimic their hosts. The European cuckoo (Cuculus canorus), for example, lays its eggs in the nests of other species that then raise the young. To prevent the host birds from rejecting her eggs, a cuckoo lays only in nests of species whose eggs resemble her own. Different species of cuckoos lay differently coloured eggs; thus each must learn which species it can successfully parasitize. It is thought that a female cuckoo learns to recognize the species by which she was raised and then seeks out nests of the same species for her own eggs. Mimicry of animal colour patterns and scents also occurs in some plants, usually for the purpose of pollination and dispersal. Additional reading Significant aspects of mimicry are discussed in Wolfgang Wickler, Mimicry in Plants and Animals (1968; originally published in German, 1968); Bastiaan J.D. Meeuse, The Story of Pollination (1961), on insectflower relationships; Hugh B. Cott, Adaptive Coloration in Animals (1940, reprinted 1966); Bertil Kullenberg, Studies in Ophrys Pollination (1961), on mimicry in orchids; and Denis Owen, Camouflage and Mimicry (1980). More research is described in Thomas Eisner and Edward O. Wilson (comps.), Animal Behavior: Readings from Scientific American (1975), and The Insects: Readings from Scientific American (1977). Types of mimicry are discussed in G. Pasteur, A Classificatory Review of Mimicry Systems, Annual Review of Ecology and Systematics, 13:169199 (1982). A series of articles in the Philosophical Transactions of the Royal Society of London, Series B, analyzes the mechanism of specific Batesian mimicS: Cyril A. Clarke, Philip M. Sheppard, and I.W.B. Thornton, The Genetics of the Mimetic Butterfly Papilio memnon L., 254:3789 (1968); Cyril A. Clarke and Philip M. Sheppard, Further Studies on the Genetics of the Mimetic Butterfly Papilio memnon L., 263:3570 (1971), and The Genetics of the Mimetic Butterfly Hypolimnas bolina L., 272:229265 (1975). Other journal articles on mimicry include J.R.G. Turner, Adaptation and Evolution in Heliconius: A Defense of Neo-Darwinism, Annual Review of Ecology and Systematics, 12:99121 (1981); on plants, D. Wiens, Mimicry in Plants, Evolutionary Biology, 11:365403 (1978); Spencer C.H. Barrett, Crop Mimicry in Weeds, Economic Botany, 37:255282 (1983), and Mimicry in Plants, Scientific American, 257(3):7683 (September 1987); and on birds, P.K. McGregor and J.R. Krebs, Song Learning and Deceptive Mimicry, Animal Behaviour, 32:280287 (1984). Wolfgang J.H. Wickler