Mimicry

"Mimic" redirects here. For other uses, see Mimic (disambiguation).

Plate from Henry Walter Bates (1862) illustrating Batesian mimicry between Dismorphia species (top row, third row) and various Ithomiini (Nymphalidae) (second row, bottom row).

In ecology, mimicry describes a situation where one organism, the mimic, has evolved to share common outward characteristics with another organism, the model, through the selective action of a signal-receiver or "dupe". Collectively this known as a mimicry complex. The model is usually another species, or less commonly, the mimic's own species, including automimicry, where one part of the body bears superficial similarity to another. The signal-receiver is typically another intermediate organism, e.g the common predator of two species, but may actually be the model itself (such as an orchid resembling a female wasp). As an interaction, mimicry is in most cases advantageous to the mimic and is always harmful to the receiver, but may increase, reduce or have no effect on the fitness of the model depending on the situation. Models themselves are difficult to define in some cases, for example eye spots may not bear resemblance to any specific organism's eyes, and camouflage often cannot be attributed to any particular model.

Camouflage, in which a species appears similar to its surroundings, is essentially a form of visual mimicry, but usually is restricted to cases where the model is not another organism. The lack of a true distinction between the two phenomena can be seen in animals that resemble twigs, bark, leaves or flowers, in that they are often classified as camouflaged (a plant constitutes its "surroundings"), but are sometimes classified as mimics (a plant is also an organism). Crypsis is a broader concept that encompasses all forms of detection evasion, such as mimicry, camouflage, hiding etc.

Though mimicry is most obvious to humans in visual mimics, it may also involve olfactory (smell) or auditory signals, and more than one type of signal may be employed. Mimicry may involve morphology, behavior, and other properties. In any case, the signal always functions to deceive the receiver by providing misleading information. In evolutionary biology terms, this phenomenon is a form of co-evolution involving an evolutionary arms race, and should not be confused with convergent evolution, which occurs when species come to resemble on another independently due to similar lifestyles.

Mimics may have multiple models during different stages of their life cycle, or they may be polymorphic, with different individuals imitating different models. Models themselves may have more than one mimic, though frequency dependent selection favors mimicry where models outnumber mimics. Models tend to be relatively closely related organisms, but mimicry of vastly different species is also known. Most known mimics are insects, though many other animal mimics including mammals are known. Plants themselves may also be mimics, though less research has been carried out on this subject. Fungi may also be involved both as models, in the induction of mimicry, or as mimics themselves.

Types of mimicry

Many types of mimicry have been described. An overview of each follows, highlighting the similarities and differences between the various forms.

Batesian

A drone fly exhibits Batesian mimicry by resembling a honey bee

Batesian mimicry is named after Henry Walter Bates, an English naturalist whose work on butterflies in the Amazon rainforest (including The Naturalist on the River Amazons) was pioneering in this field of study. In this type of mimicry the mimic sends similar signals to model species, but does not share the attribute that makes it unprofitable to predators, in this case, aposematism or warning colouration developed to indicate unpalatability.

Examples:

• Lepidoptera
  • The Ash Borer (Podosesia syringae), a moth of the Clearwing family (Sesiidae), is a Batesian mimic of the Common wasp because it resembles the wasp, but is not capable of stinging. A predator that has learned to avoid the wasp would similarly avoid the Ash Borer.
  • Plain Tiger (Danaus chrysippus) - an unpalatable model with a number of mimics.
  • Common Crow (Euploea core) - an unpalatable model with a number of mimics. See also under Müllerian mimicry below.
  • Consul fabius and Eresia eunice imitate unpalatable Heliconius butterflies such as H. ismenius (Pinheiro 1996).
  • Several palatable butterflies resemble different species from the highly noxious papilionine genus Battus (Pinheiro 1996).
  • Several palatable moths produce ultrasonic click calls to mimic the unpalatable tiger moths.
• The False Cobra (Malpolon moilensis) is a mildly venomous but harmless colubrid snake which mimics the characteristic "hood" of an Indian cobra's threat display. The Eastern Hognose Snake (Heterodon platirhinos) similarly mimics the threat display of poisonous snakes.

• Octopuses of the genus Thaumoctopus (the Mimic Octopus and the "wunderpus") are able to intentionally alter their body shape and color so that they resemble dangerous sea snakes or lionfish.[2]

Müllerian

The Heliconius butterflies from the tropics of the Western Hemisphere are the classical model for Müllerian mimicry.

Named after Fritz Müller, Müllerian mimicry describes the situation where a mimic resembles a successful species and shares the anti-predation attribute (dangerous or unpalatable.) This type of mimicry is unique in that both the mimic and the model benefit from the interaction, which could thus be classified as mutualism in this respect.

Examples:

• Lepidoptera
  • The Monarch Butterfly (Danaus plexippus) is a member of a Müllerian complex with the Viceroy butterfly (Limenitis archippus) in shared coloration patterns and display behavior. The Viceroy has subspecies with somewhat different coloration, each one very closely matching the local Danaus species. E.g., in Florida, the pairing is of the Viceroy and the Queen Butterfly, and in Mexico, the Viceroy resembles the Soldier Butterfly. Therefore, the Viceroy is a single species involved in three different Müllerian pairs. This example was long believed to be a case of Batesian mimicry, with the Viceroy being the mimic and the Monarch the model, but it was more recently determined that the Viceroy is actually the more unpalatable species, though there is considerable individual variation. While L. archippus is really bad-tasting, Danaus species tend to be toxic rather than just repugnant, due to their different food plants.
  • Unpalatable Euploea species look very similar. See also under Batesian mimicry above.
  • The genus Morpho is palatable but are very strong fliers; birds - even species which are specialized for catching butterflies on the wing - find it very hard to catch them. The conspicuous blue coloration shared by most Morpho species seems to be a case of Müllerian mimicry (Pinheiro 1996).
  • The "orange complex" of species, including the heliconiines Agraulis vanillae, Dryadula phaetusa, and Dryas iulia which all taste bad.
  • Many different tiger moths make ultrasonic clicking calls to warn bats that they are unpalatable. Presumably a bat may learn to avoid any signalling moths, which would make this an example of Müllerian mimicry.
• Various bees and numerous vespid and sphecoid wasps: These animals are examples of Müllerian mimics because they have the aposematic yellow and black stripes (sometimes black and red, or black and white). All are potentially harmful to predators, fulfilling the second requirement of Müllerian mimicry.

Mertensian

Texas Coral Snake, Micrurus tener

Mertensian mimicry is named after the late German herpetologist Robert Mertens, and is often considered a subtype of Müllerian mimicry. In this case both harmless and deadly mimics resemble a dangerous but not usually deadly species (if the predator dies, it cannot learn to recognize a trait, e.g. a warning coloration).

Examples:

• Some Milk Snake (Lampropeltis triangulum) subspecies (harmless), the moderately toxic False Coral Snakes (genus Erythrolamprus), and the deadly Coral Snakes all have a red background color with black and white/yellow stripes. In this system, both the milk snakes and the deadly coral snakes are mimics, whereas the false coral snakes are the model.

Aggressive

Aggressive mimicry (also known as Peckhamian mimicry after Elizabeth Maria Gifford Peckham) describes predators which resemble a harmless species, allowing them greater success in capturing prey. This may either be the prey species' own prey (in which case they are actively lured) or another harmless species such as a mutualistic symbiont of the prey.

Examples:

The Alligator Snapping Turtle uses its tongue to lure fish.

• Female fireflies of the genus Photuris copy the light signals of other species, thereby attracting male fireflies which are then captured and eaten.
• The Alligator Snapping Turtle (Macrochelys temminckii) is a well-camouflaged ambush predator. Its tongue bears a conspicuous pink extension that resembles a worm and can be wriggled around; fish that try to eat the "worm" get in turn eaten by the turtle.
• The Zone-Tailed Hawk resembles the Turkey Vulture. It flies amongst them, suddenly breaking from the formation and ambushing its prey.

Vavilovian

Vavilovian mimicry or weed mimicry is named after Nikolai Ivanovich Vavilov, a prominent Russian botanist and geneticist who identified the centres of origin of cultivated plants and later died in prison during the days of Lysenkoism. In this form of mimicry, the mimic comes to resemble a domesticated plant through generations of artificial selection, and may eventually be domesticated itself. This type of mimicry does not occur in ecosystems unaltered by humans.

Examples:

• Echinochloa oryzoides is a species of grass which is found as a weed in rice (Oryza sativa) fields. The plant looks similar to rice and its seeds are often mixed in rice and difficult to separate. This close similarity was enhanced by the weeding process which is a selective force that increases the similarity of the weed in each subsequent generation.

Bakerian

Lobelia cardinalis is believed to be a Bakerian mimic, attracting humming birds without producing nectar.

Bakerian mimicry, named after Herbert G. Baker, occurs where the mimic resembles members of its own or other species, luring pollinators or reaping other benefits, although the mimicry may not be readily apparent due to the fact that the members of the same species may still exhibit sexual dimorphism.

Examples:

• Common in many species of Caricaceae. Their flowers have little or no nectar but resemble nectar-producing flowers. Pollinators will be fooled into visiting them and thus fertilization is ensured without having to produce a reward for the pollinator.

Automimicry

Automimicry involves the mimic having some part of its body resembling some other part. Examples include snakes in which the tail resembles the head and show behavior such as moving backwards to confuse predators and insects and fishes with eyespots on their hind ends to resemble the head. The term is also used when the mimic imitates other morphs within the same species such as some males looking like females or vice versa. Examples:

• Many insects have filamentous "tails" at the ends of their wings which are combined with patterns of markings on the wings themselves to create a "false head" which misdirects predators (e.g., hairstreak butterflies).
• Several pygmy owls bear "false eyes" on the back of their head to fool predators into believing the owl is alert to their presence.
• The yellow throated males of the Common Side-blotched Lizard use a 'sneaking' strategy in mating. They look and behave like unreceptive females. This strategy is effective against 'usurper' males with orange throats, but ineffective against blue throated 'guarder' males, which will chase them away.
• Female hyenas have pseudo-penises which make them look like males.

Other

Some hawk-cuckoos resemble sparrow-hawks.

• Owl butterflies (genus Caligo) bear eye-spots on the underside of their wings; if turned upside-down, their undersides resemble [3] the face of an owl (such as the Short-eared Owl or the Tropical Screech Owl) for which in turn the butterfly predators - small lizards and birds - would be food. Thus it has been supposed that the eye-spots are a form of Batesian mimicry. However, the pose in which the butterfly resembles an owl's head is not normally adopted in life. While the eye-spots indeed seem to have an anti-predation function, their actual role remains elusive; they are most probably some sort of automimicry.

Mimicry and convergent evolution

It was sometimes assumed that mimicry evolves as a positive adaptation; that is, the mimic gains fitness via convergent evolution which results in resemblance to another species. However, there are others who suggest that evolution is non-adaptive or merely a result of structural similarities, e.g., the lepidopterist (and sometime author) Vladimir Nabokov argued that much of insect mimicry, including the Viceroy/Monarch mimicry, resulted from the fact that coloration patterns in both species simply had a common structural basis, and thus the tendency for convergence by chance was high. However, this very example provides evidence precisely to the contrary, as the viceroy's color pattern is completely unlike any of the species to which it is closely related, and the viceroy itself has three color forms, each adapted to resemble a different species of Danaus. Likewise, this example is based on two organisms that are indeed fairly similar in structure (both butterflies), while a great many cases of mimicry (especially in large Batesian/Mũllerian complexes) involve insects from multiple orders that share virtually no structural similarities whatsoever (e.g., beetles, true bugs, moths, wasps, bees, and flies may all belong to a single mimetic complex, despite profound differences).

See also

• Animal colouration
• Ant mimicry
• Aposematism
• Biomimicry
• Code-breaking
• Molecular mimicry

Further reading

• Cott, H.B. (1940) Adaptive Coloration in Animals. Methuen and Co, Ltd., London ISBN 0416300502
• Wickler, W. (1968) Mimicry in Plants and Animals (Translated from the German) McGraw-Hill, New York. ISBN 0070701008
• Owen, D. (1980) Camouflage and Mimicry. Oxford University Press ISBN 0192176838
• Pasteur, Georges (1982). “A classificatory review of mimicry systems”. Annual Review of Ecology and Systematics 13: 169–199.
• Brower, L. (ed.) (1988). Mimicry and the Evolutionary Process. Chicago: The University of Chicago Press. ISBN 0226076083

External links

• Warning Colour and Mimicry Lecture outline from University College London
• Camouflage and Mimicry in Fossils
• Chemical Mimicry in Pollination
• Telling the difference between Wunderpus and The Mimic Octopus