Müllerian mimicry

Müllerian mimicry is a type of biological mimicry in which two or more well-defended species, often foul-tasting and sharing common predators, converge in appearance to mimic each other's honest warning signals. This convergence of appearance achieves the following benefit to species that undergo it: predators need only experience a single unpleasant encounter with any member of a set of Müllerian mimics in order to thereafter avoid all creatures of similar appearance, whether or not it is the same species as the initial encounter. A ring of distinct species is thereby protected from their mutual predators by attempted predation upon any one of its members. The phenomenon is named after the German-Brazilian naturalist Fritz Müller, who proposed the concept in 1878, supporting his theory with a mathematical model of frequency-dependent selection, one of the first such models anywhere in biology.^[a][2][3]

Müllerian mimicry was first identified in tropical butterflies that shared colourful wing patterns, but it is found in many groups of insects such as bumblebees, as well as in other animals such as poison frogs and coral snakes. The mimicry need not be restricted to that detected by vision—many snakes share auditory warning signals. Similarly, the defences involved are not limited to toxicity—anything that tends to deter predators, such as foul taste, sharp spines, or defensive behaviour can make a species unprofitable enough to predators to allow Müllerian mimicry to develop.

Once a pair of Müllerian mimics has formed other mimics may join them by advergent evolution (one species changing to conform to the appearance of the pair, rather than mutual convergence), forming mimicry rings. Large rings are found among the several thousand species of velvet ants (which are all, in fact, types of wasp). Because the frequency of mimics in a given environment is positively correlated with an individual mimic's survival, the rarer mimics come to resemble commoner models, favouring both advergence and ever-larger rings of Müllerian mimicry. Where Müllerian mimics are not strongly protected by venom or other defences, honest Müllerian mimicry incrementally transforms into the better-known bluffing of Batesian mimicry.

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