Mimicry
Mimicry
Mimicry may broadly be defined as imitation or copying of an action or image. In biological systems, mimicry specifically refers to the fascinating resemblance
of an organism, called the “mimic,” to another somewhat distantly related organism, called the “model.” The set of mimic and model species involved is often referred to as a mimicry complex. Usually through escape from predation, the mimicry of a trait or traits helps the mimic to survive. This, coupled with the fact that the resemblance traits are genetically based, implies that mimicry complexes have been shaped by natural selection. There are two major types of mimicry, Batesian and Müllerian, named after the naturalists that first theorized them upon their observations of butterflies. There are a few other types that are not as prevalent, such as aggressive mimicry.
Batesian mimicry
In 1862, H.W. Bates presented an hypothesis explaining the similar color patterns in several species sets of tropical butterflies in different families. His hypothesis was one of the early applications of Charles Darwin’s theory of natural selection. Bates reasoned that an edible butterfly species that was susceptible to predation would evolve, due to selection by a bird predator, to look like an unpalatable, or distasteful model species. If the mimic was rarer than the model, then birds would encounter the distasteful model more frequently, and would learn to avoid all butterflies that looked like the distasteful ones. In fact, the relative rarity of the model was to Bates a prerequisite for such a phenomenon to evolve. As mimicry theory has progressed, mathematical models show that relative abundances of models and mimics, as well as relative palatability of the two species, will determine the outcome.
Müllerian mimicry
In the 1870s, Fritz Müller theorized a different type of mimicry. His idea, also based on sets of butterfly species, was that several species, all somewhat distasteful, would evolve to look like each other. Such an evolutionary strategy would, in effect, reduce predation on any of the species because the predator would learn to avoid a single color pattern, but since all of them had the same pattern, they would all be safe from predation. The rarer form, say species 1, would eventually converge to look like the more common form, species 2, as the individuals that looked too different from species 2 would be rapidly selected out by predators. Since species 2 was more common, the predator would have had more experience with it and would have had more opportunity to learn to avoid it than with species 1, the rare species. Individuals of species 1 that resembled species 2 would benefit from the
KEY TERMS
Aggressive mimicry— A type of evolved mimicry in which the result of the mimicry is predation by the mimic on a naive “dupe.”
Batesian mimicry— A type of mimicry in which a palatable species has evolved to look like an unpalatable one in order to escape predation.
Müllerian mimicry— A type of mimicry in which two or more species evolve toward a similar appearance so that learned avoidance by a predator will result in fewer deaths for any given species.
predator’s learned avoidance of species 2, and thus would proliferate. The species would evolve to share a similar pattern as relative frequencies shifted. If the two species were equal in abundance, Müller reasoned, it would not be possible to distinguish mimic from model, as both had converged on a common phenotype, or appearance.
Aggressive mimicry
A less common but equally fascinating type of mimicry involves not only a model and a mimic, but a “dupe” species that is tricked by the mimicry. In the previously noted types of mimicry, the dupe is the predator who is tricked out of a potential food source, but in aggressive mimicry, the word is especially appropriate as being duped lethal. In aggressive mimicry, the mimic is a predator who imitates, usually in behavior, a model species in order to draw in a dupe, who then becomes prey. An example of this occurs in spiders of the family Mimetidae (mimic), who attempting to draw in spiders of other species (dupe) as prey items, produce vibrations on the webs of the dupe that mimic the prey items (model) of the dupe. When the dupe is tricked, and approaches what it thinks is food, the mimic attacks it and eats it. Bolus spiders are another type of aggressive mimic. They produce chemicals that mimic the sex pheromones of particular moth species. When male moths approach what they perceive to be a female in order to mate with her, they are caught by the bolus spider and become prey.
Resources
BOOKS
Gilbert, L.E. “Coevolution and Mimicry.” In Coevolution. Edited by D.J. Futuyma and M. Slatkin. Sunderland, MA: Sinauer Associates, Inc., 1983.
Vane-Wright, R.I. “Mimicry and Its Unknown Ecological Consequences.” In The Evolving Biosphere. Edited by P.H. Greenwood, 157-168. New York: Cambridge University Press, 1980.
OTHER
MongaBay.com. “The Arts of Deceeption” <http://rainforests.mongabay.com/0306.htm> (accessed December 4, 2006)
University College London. “General Information on Mimicry: Mimicry & Warning Colour” <http://www.ucl.ac.uk/taxome/jim/Mim/mimicry.html> (accessed December 4, 2006)
Puja Batra
Mimicry
Mimicry
Mimicry may broadly be defined as imitation or copying of an action or image. In biological systems, mimicry specifically refers to the fascinating resemblance of an organism , called the "mimic," to another somewhat distantly related organism, called the "model." The set of mimic and model species involved is often referred to as a mimicry complex. Usually through escape from predation, the mimicry of a trait or traits helps the mimic to survive. This, coupled with the fact that the resemblance traits are genetically based, implies that mimicry complexes have been shaped by natural selection . There are two major types of mimicry, Batesian and Müllerian, named after the naturalists that first theorized them upon their observations of butterflies . There are a few other types that are not as prevalent, such as aggressive mimicry.
Batesian mimicry
In 1862, H.W. Bates presented an hypothesis explaining the similar color patterns in several species sets of tropical butterflies in different families. His hypothesis was one of the early applications of Charles Darwin's theory of natural selection. Bates reasoned that an edible butterfly species that was susceptible to predation would evolve, due to selection by a bird predator , to look like an unpalatable, or distasteful model species. If the mimic was rarer than the model, then birds would encounter the distasteful model more frequently, and would learn to avoid all butterflies that looked like the distasteful ones. In fact, the relative rarity of the model was to Bates a prerequisite for such a phenomenon to evolve. As mimicry theory has progressed, mathematical models show that relative abundances of models and mimics, as well as relative palatability of the two species, will determine the outcome.
Müllerian mimicry
In the 1870s, Fritz Müller theorized a different type of mimicry. His idea, also based on sets of butterfly species, was that several species, all somewhat distasteful, would evolve to look like each other. Such an evolutionary strategy would, in effect, reduce predation on any of the species because the predator would learn to avoid a single color pattern, but since all of them had the same pattern, they would all be safe from predation. The rarer form, say species 1, would eventually converge to look like the more common form, species 2, as the individuals that looked too different from species 2 would be rapidly selected out by predators. Since species 2 was more common, the predator would have had more experience with it and would have had more opportunity to learn to avoid it than with species 1, the rare species. Individuals of species 1 that resembled species 2 would benefit from the predator's learned avoidance of species 2, and thus would proliferate. The species would evolve to share a similar pattern as relative frequencies shifted. If the two species were equal in abundance, Müller reasoned, it would not be possible to distinguish mimic from model, as both had converged on a common phenotype, or appearance.
Aggressive mimicry
A less common but equally fascinating type of mimicry involves not only a model and a mimic, but a "dupe" species that is tricked by the mimicry. In the previously noted types of mimicry, the dupe is the predator who is tricked out of a potential food source, but in aggressive mimicry, the word is especially appropriate as being duped is lethal. In aggressive mimicry, the mimic is a predator who imitates, usually in behavior , a model species in order to draw in a dupe, who then becomes prey . An example of this occurs in spiders of the family Mimetidae (mimic), who attempting to draw in spiders of other species (dupe) as prey items, produce vibrations on the webs of the dupe that mimic the prey items (model) of the dupe. When the dupe is tricked, and approaches what it thinks is food, the mimic attacks it and eats it. Bolus spiders are another type of aggressive mimic. They produce chemicals that mimic the sex pheromones of particular moth species. When male moths approach what they perceive to be a female in order to mate with her, they are caught by the bolus spider and become prey.
Resources
books
Gilbert, L.E. "Coevolution and Mimicry." In Coevolution Edited by D.J. Futuyma and M. Slatkin. Sunderland, MA: Sinauer Associates, Inc., 1983.
Vane-Wright, R.I. "Mimicry and its Unknown Ecological Consequences." In The Evolving Biosphere. edited by P.H. Greenwood, 157-168. New York: Cambridge University Press, 1980.
Puja Batra
KEY TERMS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .- Aggressive mimicry
—A type of evolved mimicry in which the result of the mimicry is predation by the mimic on a naive "dupe."
- Batesian mimicry
—A type of mimicry in which a palatable species has evolved to look like an unpalatable one in order to escape predation.
- Müllerian mimicry
—A type of mimicry in which two or more species evolve toward a similar appearance so that learned avoidance by a predator will result in fewer deaths for any given species.
Mimicry
Mimicry
Animals that are toxic, armed with spines, or are otherwise unpalatable, or disagreeable, to predators often exhibit conspicuous colors or patterns. These superficial characteristics, called aposematic signals, are used to warn potential predators of the animal's physical or chemical defenses. The distinct colorations are highly conspicuous against certain backgrounds. This imposes a cost on the aposematic prey because the predators can more readily spot them. However, the predators will also be quick to learn and remember which prey to avoid because of the distinctiveness of the signals. Of course, if the prey is not sufficiently unpalatable, then the costs are greater than the benefits for the attacked animal.
To evaluate whether the benefits outweigh the costs of any predator/prey strategy, the Evolutionary Stable Strategy (ESS) should be taken into account. The ESS is a strategy that, when common among members of a particular role—such as aposematic coloration of prey—is not invaded or displaced over evolutionary time by any rare alternative. In addition, at evolutionary stability, each role has its own ESS.
An important aspect of aposematic signaling is the evolution of another defense, mimicry. A mimic is a predator or prey that bears a superficial resemblance to another species. The mimic resembles the model, which exhibits aposematic coloration. There are two forms of mimicry: Batesian mimicry and Mullerian mimicry.
In Batesian mimicry, a palatable species mimics an unpalatable model, thereby gaining protection through the traits of another species. For example, juveniles of the harmless lizard species Heliobolus lugubris, inhabitants of the Kalahari Desert of southern Africa, mimic the color and posture of the ooglister beetle, a species that sprays noxious fluids at predators. As the lizards mature and grow larger than the average beetle, they develop cryptic coloration as a line of defense.
Another example is the monarch butterfly. Monarch butterflies store cardiac poisons acquired from milkweed plants they eat as larvae and are therefore distasteful and potentially harmful to other species. Viceroy butterflies, by contrast, are harmless and palatable and so need a good defense to ward off predators. The viceroy is protected by having wings of the same coloration pattern as the monarch butterfly. Many innocuous snakes mimic the conspicuous red, white, and black markings of the poisonous coral snake in an attempt to protect themselves.
It is important to note that for Batesian mimicry to be effective, there must be a larger population of models than mimics so that predators are not clued in to the fact that they are being tricked.
Mullerian mimicry involves two or more unpalatable, aposematically colored species that resemble each other in appearance. This strategy evolved so that predators will learn more quickly to avoid animals with particular warning signs.
Some predators practice a reverse mimicry in order to trap their prey. Some species of snapping turtles, for example, have tongues that resemble wriggling worms. By sticking their tongues in the water, these turtles are able to lure small fish that are looking for a meal of worms.
Although mimicry seems a rather straightforward tactic, several conditions must be met in order for it to function as an ESS. The first condition for the strategy to be successful is that very conspicuous signals of aposematic coloration should be avoided so that it is somewhat difficult for predators to learn to avoid the aposematically patterned prey. Second, increasing prey unpalatability should increase the chances that any attacked prey will survive because the predator will quickly learn species avoidance after attacking the prey. It is important to note that the degrees of unpalatability and signal conspicuousness at ESS depend on the predators' patterns of learning .
Despite all the warning patterns and colors, predators do sample aposematic prey on occasion. And although Mullerian mimicry is found among quite a few species, Batesian mimicry is considered a rare defensive strategy. The balance between the employment of mimicry and its success rate supports the notion that these aposematic signals are a relevant ESS.
Danielle Schnur
Bibliography
Begon, Michael, John L. Harper, and Colin R. Townsend. Ecology, 2nd ed. New York: Blackwell Scientific, 1990.
Bradbury, Jack W., and Sandra L. Vehrencamp. Principles of Animal Communication. Sunderland, MA: Sinauer, 1998.
Campbell, Neil A. Biology, 3rd ed. Redwood City, CA: Benjamin/Cummings Publishing Company, Inc., 1993.
Mimicry
442. Mimicry
- chameleon lizard able to change the color of its skin to match brown or green surroundings; has come to mean ‘inconstant person.’ [Western Culture: Misc.]
- Costard apes Elizabethan courtly language. [Br. Lit.: Love’s Labour’s Lost ]
- Doolittle, Eliza slum girl taught by professor to imitate upper class. [Br. Lit.: Pygmalion ]
- lyrebird Australian bird; one of the most famous mimic species. [Ornithology: Sparks, 116]
- mockingbird noted for mimicking songs of other birds; one of the world’s most noted singers. [Ornithology: Sparks, 116]
- monkey known to copy human actions. [Western Cult.: Misc.]
- myna certain species are able to mimic human speech and other sounds. [Ornithology: Sparks]
- parrot bird able to mimic human speech; hence, parrot ‘to repeat or imitate.’ [Western Culture: Misc.]
mimicry
mim·ic·ry / ˈmiməkrē/ • n. (pl. -ries) the action or art of imitating someone or something, typically in order to entertain or ridicule: the word was spoken with gently teasing mimicry | a playful mimicry of the techniques of realist writers. ∎ Biol. the close external resemblance of an animal or plant (or part of one) to another animal, plant, or inanimate object. See also Batesian mimicry, Müllerian mimicry.