Müllerian mimicry

Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimic each other's honest warning signals, to their mutual benefit.

[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, and other animals such as poison frogs and coral snakes.

An early proponent of evolution, Müller offered the first explanation for resemblance between certain butterflies that had puzzled the English naturalist Henry Walter Bates in 1862.

Dangerous organisms with these honest signals are avoided by predators, which quickly learn after a bad experience not to pursue the same unprofitable prey again.

[14] The underlying concept with predators that learn is that the warning signal makes the harmful organism easier to remember than if it remained as well camouflaged as possible.

Many animals remain inconspicuous until threatened, then suddenly employ warning signals, such as startling eyespots, bright colours on their undersides or loud vocalizations.

Müller thus provided an explanation for Bates' paradox; the mimicry was not, in his view, a case of exploitation by one species, but rather a mutualistic arrangement, though his mathematical model indicated a pronounced asymmetry.

Mitochondrial DNA analysis of admiral butterflies shows that the viceroy is the basal lineage of two western sister species in North America.

This implies that it is reproductively beneficial for both species if the models outnumber the mimics; this increases the negative interactions between predator and prey.

The Optix gene is responsible for the Heliconius butterflies' signature red wing patterns that help it signal to predators that it is toxic.

This states that a large mutational leap initially establishes an approximate resemblance of the mimic to the model, both species already being aposematic.

The mechanism was proposed by the entomologist F. A. Dixey in 1909[25] and has remained controversial; the evolutionary biologist James Mallet, reviewing the situation in 2001, suggested that in Müllerian mimicry, advergence may be more common than convergence.

This does not appear to happen in nature, however, as Heliconius butterflies form multiple Müllerian mimicry rings in a single geographical area.

Bumblebees Bombus are all aposematically coloured in combinations, often stripes, of black, white, yellow, and red; and all their females have stings,[c] so they are certainly unprofitable to predators.

There is evidence that several species of bumblebees in each of several areas of the world, namely the American West and East coasts, Western Europe, and Kashmir, have converged or adverged on mutually mimetic coloration patterns.

[31] It has been proposed that spiny plants such as Cactaceae and Agave in the Americas, Aloe, Euphorbia, white-thorned Acacia in Africa and spiny Asteraceae of the Mediterranean may form Müllerian mimicry rings, as they are strongly defended, are generally agreed to be aposematic, have similar conspicuous patterns and coloration, and are found in overlapping territories.

[32] Aposematic mammals in the families Mustelidae, Viverridae, and Herpestidae have independently evolved conspicuous black-and-white coloration, suggesting that Müllerian mimicry may be involved.

[30] The evolutionary zoologist Thomas N. Sherratt suggests that different types of mimicry occur in brand and product marketing.

He notes that distinctive forms like the Coca-Cola bottle's shape are defended by businesses, whereas rival companies have often imitated such famous motifs to benefit from the investment and reputation of their well-known competitors, constituting Batesian mimicry.

Sherratt observes that the packaging of British supermarket own brands of potato crisps are consistently colour-coded red for the ready-salted variety, green for salt and vinegar, and blue for cheese and onion,[d] across the major chains Sainsbury's, Tesco, Asda, and Waitrose.

He argues that this sharing of pattern is very unlikely to have arisen by chance, in which case the resemblance is intentionally to inform customers reliably (honest signalling) of what each package contains, to mutual benefit in the manner of Müllerian mimicry.

Two examples of Müllerian mimicry in Heliconius butterflies: In this image the top four are forms of Heliconius numata , which mimic species from the genus Melinaea , while the bottom four are H. melpomene (left) and H. erato (right), which mimic each other. [ 1 ]
The viceroy butterfly (top) appears very similar to the noxious-tasting monarch butterfly (bottom). Although it was for a long time purported to be an example of Batesian mimicry , the viceroy has recently been discovered to be just as unpalatable as the monarch, making this a case of Müllerian mimicry. [ 4 ]
Batesian vs Müllerian mimicry: the former is deceptive, the latter honest.
Comparison of Batesian and Müllerian mimicry, illustrated with a hoverfly , a wasp and a bee
Formation of Müllerian mimicry rings by a process of advergence of one species or pair of mimics to another, presumably larger or more abundant. Evolution is shown on two axes denoting phenotypes for convenience; in practice there would be any number of dimensions (e.g. coloration features). The model predicts a single mimicry ring in an area, but this is not the case in Heliconius butterflies. [ 22 ]
A common morph of Ranitomeya (Dendrobates) imitator is aposematically striped black and yellow, but in other areas, other morphs imitate differently coloured species.
Many species of North American velvet ants in the genus Dasymutilla are involved in mimicry complexes.
Pitohui kirhocephalus , from Duperrey , 1825–1839, appears to be a Müllerian mimic of Pitohui dichrous in some of its plumage types.
Several mammals including the Saharan striped polecat , Ictonyx libycus , are aggressive, aposematically coloured predators. They share black-and-white patterns, suggesting Müllerian mimicry. [ 30 ]