Mimicry | Research & Encyclopedia Articles

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.

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.

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.

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 as 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.