Müllerian mimicry

Müllerian mimicry

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Müllerian mimicry is a natural phenomenon when two or more harmful species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals
Aposematism
Aposematism , perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators...

. It is named after the German naturalist Fritz Müller
Fritz Müller
Johann Friedrich Theodor Müller , better known as Fritz Müller, and also as Müller-Desterro, was a German biologist and physician who emigrated to southern Brazil, where he lived in and near the German community of Blumenau, Santa Catarina...

, who first proposed the concept in 1878.

It can be contrasted with Batesian mimicry
Batesian mimicry
Batesian mimicry is a form of mimicry typified by a situation where a harmless species has evolved to imitate the warning signals of a harmful species directed at a common predator...

, where a harmless organism imitating the protected species is referred to as the mimic and the dangerous one being imitated the model. Müllerian mimicry differs because both parties are harmful; each mimics the other species, while serving as a model at the same time. If one species is encountered far less than the other, the more common species could be treated as the model and the other the mimic. However, if they are encountered in similar numbers they would best be termed comimics or mimic-models. The predator mediating indirect convergence between these two parties is known as the signal receiver or dupe, though the latter term is less relevant here, as they are not actually deceived
Deception
Deception, beguilement, deceit, bluff, mystification, bad faith, and subterfuge are acts to propagate beliefs that are not true, or not the whole truth . Deception can involve dissimulation, propaganda, and sleight of hand. It can employ distraction, camouflage or concealment...

 about the harmful qualities of their prey; both prey provide an honest warning signal
Signalling theory
Within evolutionary biology, signalling theory is a body of theoretical work examining communication between individuals. The central question is when organisms with conflicting interests should be expected to communicate "honestly"...

. For this reason, Georges Pasteur has asserted that it is not a form of mimicry at all, as no deception is involved. Unlike other mimicry systems, the signal receiver is better off for mistaking one harmful species for another, as it avoids the potential harm involved.

However, because comimics may have differing degrees of protection, the distinction between Müllerian and Batesian mimicry is not absolute, and there can be said to be a spectrum between the two forms. Additionally, a species may be a Batesian mimic to one predator and a Müllerian mimic to another. While Batesian and Müllerian mimicry are commonly given examples of mimicry, there is often little or no mention of other forms. There are many other types of mimicry however, some very similar in principle, others far separated. For example in aggressive mimicry
Aggressive mimicry
Aggressive mimicry is a form of mimicry where predators, parasites or parasitoids share similar signals with a harmless model, allowing them to avoid being correctly identified by their prey or host...

 a predator might mimic the food of its prey, luring them towards it and improving its foraging
Foraging
- Definitions and significance of foraging behavior :Foraging is the act of searching for and exploiting food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce...

 success.

Müllerian mimicry need not involve visual
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...

 mimicry; it may employ any of the sense
Sense
Senses are physiological capacities of organisms that provide inputs for perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology , and philosophy of perception...

s. For example, many snakes share the same auditory
Hearing (sense)
Hearing is the ability to perceive sound by detecting vibrations through an organ such as the ear. It is one of the traditional five senses...

 warning signals, forming an auditory Müllerian mimicry ring. More than one common signal may show convergences by the parties. While model and mimic are often closely related
Common descent
In evolutionary biology, a group of organisms share common descent if they have a common ancestor. There is strong quantitative support for the theory that all living organisms on Earth are descended from a common ancestor....

 species, Müllerian mimicry between very distantly related taxa also occurs.

Background


Müllerian mimicry was proposed by the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 zoologist
Zoology
Zoology |zoölogy]]), is the branch of biology that relates to the animal kingdom, including the structure, embryology, evolution, classification, habits, and distribution of all animals, both living and extinct...

 and naturalist
Natural history
Natural history is the scientific research of plants or animals, leaning more towards observational rather than experimental methods of study, and encompasses more research published in magazines than in academic journals. Grouped among the natural sciences, natural history is the systematic study...

 Johann Friedrich Theodor Müller (1821–1897), always known as Fritz. An early proponent of evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

, Müller offered the first explanation for resemblance between certain butterflies that had puzzled the English naturalist Henry Walter Bates
Henry Walter Bates
Henry Walter Bates FRS FLS FGS was an English naturalist and explorer who gave the first scientific account of mimicry in animals. He was most famous for his expedition to the Amazon with Alfred Russel Wallace in 1848. Wallace returned in 1852, but lost his collection in a shipwreck...

, who, like Müller, spent a significant part of his life in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

. Müller had also seen these butterflies first hand, and collected specimens like Bates.

Understanding Müllerian mimicry is impossible without first understanding aposematism
Aposematism
Aposematism , perhaps most commonly known in the context of warning colouration, describes a family of antipredator adaptations where a warning signal is associated with the unprofitability of a prey item to potential predators...

, or warning signals. Dangerous organisms with these aposematic signals are avoided by predators, who quickly learn after a bad experience not to pursue the same prey again. Learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...

 is not actually necessary for animals which instinct
Instinct
Instinct or innate behavior is the inherent inclination of a living organism toward a particular behavior.The simplest example of an instinctive behavior is a fixed action pattern, in which a very short to medium length sequence of actions, without variation, are carried out in response to a...

ively avoid certain prey; however, learning from experience is much more common. The underlying concept with predators that learn is that the warning signal makes the harmful organism easier to remember than if it remained as cryptic
Crypsis
In ecology, crypsis is the ability of an organism to avoid observation or detection by other organisms. It may be either a predation strategy or an antipredator adaptation, and methods include camouflage, nocturnality, subterranean lifestyle, transparency, and mimicry...

 as possible (e.g. being still and silent, providing no scent, and blending in with the background). Aposematism and crypsis are in this way opposing concepts, but this does not mean they are mutually exclusive. Many animals remain inconspicuous until threatened, then suddenly employ warning signals, such as bright colors on their undersides or loud vocalizations. In this way, they enjoy the best of both strategies.

Many different prey of the same predator may employ separate warning colors, but this makes no sense for any party. Surely if they could all get together and agree on a common warning signal, the predator would have fewer detrimental experiences, and the prey would lose fewer individuals educating it. But no such conference needs to take place, as a prey species that just so happens to look a little like a harmful species will be safer than its conspecifics, leading to a tendency toward a single warning language. This can lead to the evolution of both Batesian and Müllerian mimicry, depending on whether the prey is harmful, as well, or just a freerider. Multiple species can join this protective cooperative, expanding the mimicry ring.

Müller thus provided an explanation for 'Bates' paradox'; the mimicry was not a case of exploitation by one species, but rather a mutualistic arrangement.

Further reading

  • Wickler, W.
    Wolfgang Wickler
    Wolfgang Wickler is a German zoologist, behavioral researcher and publicist. As of 1974, he led the ethological department of the Max Planck Institute for Behavioral Physiology in Seewiesen near Starnberg and he took over as director of the institute in 1975...

     (1968) Mimicry in Plants and Animals (Translated from the German) McGraw-Hill, New York. ISBN 0070701008 Especially chapters 7 and 8.
  • Ruxton, G. D.
    Graeme Ruxton
    Graeme Ruxton is Professor of theoretical ecology at the University of Glasgow, Scotland, United Kingdom. His studies focus on the evolutionary pressures on aggregation by animals, and predator-prey aspects of sensory ecology...

    ; Speed, M. P.; Sherratt, T. N. (2004). Avoiding Attack. The Evolutionary Ecology of Crypsis, Warning Signals and Mimicry. Oxford: Oxford University Press. ISBN 0198528604 Chapter 9 and 11 provide an overview of current understanding