In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. Often, mimicry functions to protect a species from predators, making it an antipredator adaptation. Mimicry evolves if a receiver (such as a predator) perceives the similarity between a mimic (the organism that has a resemblance) and a model (the organism it resembles) and as a result changes its behaviour in a way that provides a selective advantage to the mimic. The resemblances that evolve in mimicry can be visual, acoustic, chemical, tactile, or electric, or combinations of these sensory modalities. Mimicry may be to the advantage of both organisms that share a resemblance, in which case it is a form of mutualism; or mimicry can be to the detriment of one, making it parasitic or competitive. The evolutionary convergence between groups is driven by the selective action of a signal-receiver or dupe. Birds, for example, use sight to identify palatable insects, whilst avoiding the noxious ones. Over time, palatable insects may evolve to resemble noxious ones, making them mimics and the noxious ones models. In the case of mutualism, sometimes both groups are referred to as "co-mimics". It is often thought that models must be more abundant than mimics, but this is not so. Mimicry may involve numerous species; many harmless species such as hoverflies are Batesian mimics of strongly defended species such as wasps, while many such well-defended species form Mullerian mimicry rings, all resembling each other. Mimicry between prey species and their predators often involves three or more species.
In its broadest definition, mimicry can include non-living models.
Mimicry can result in an evolutionary arms race if mimicry negatively affects the model, and the model can evolve a different appearance from the mimic. p161 Mimicry should not be confused with other forms of convergent evolution that occurs when species come to resemble each other by adapting to similar lifestyles that have nothing to do with a common signal receiver. Mimics may have different models for different life cycle stages, or they may be polymorphic, with different individuals imitating different models, such as in Heliconius butterflies. Models themselves may have more than one mimic, though frequency dependent selection favours 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 examples including vertebrates are also known. Plants and fungi may also be mimics, though less research has been carried out in this area.
Use of the word mimicry dates to 1637. It derives from the Greek term mimetikos, "imitative", in turn from mimetos, the verbal adjective of mimeisthai, "to imitate". Originally used to describe people, "mimetic" was used in zoology from 1851, "mimicry" from 1861.
Many types of mimicry have been described.
Defensive or protective mimicry takes place when organisms are able to avoid harmful encounters by deceiving enemies into treating them as something else.
The first three such cases discussed here entail mimicry of animals protected by warning coloration:
- Batesian mimicry, where a harmless mimic poses as harmful.
- Müllerian mimicry, where two or more harmful species mutually advertise themselves as harmful.
- Mertensian mimicry, where a deadly mimic resembles a less harmful but lesson-teaching model.
The fourth case, Vavilovian mimicry, where weeds resemble crops, involves humans as the agent of selection.
In Batesian mimicry the mimic shares signals similar to the model, but does not have the attribute that makes it unprofitable to predators (e.g., unpalatability).
There are many Batesian mimics in the order Lepidoptera. Consul fabius and Eresia eunice imitate unpalatable Heliconius butterflies such as H. ismenius. Limenitis arthemis imitate the poisonous pipeline swallowtail (Battus philenor). Several palatable moths produce ultrasonic click calls to mimic unpalatable tiger moths. Octopuses of the genus Thaumoctopus (the mimic octopus) are able to intentionally alter their body shape and coloration to resemble dangerous sea snakes or lionfish. In the Amazon, the helmeted woodpecker (Dryocopus galeatus), a rare species which lives in the Atlantic Forest of Brazil, Paraguay, and Argentina, has a similar red crest, black back, and barred underside to two larger woodpeckers: Dryocopus lineatus]]ndCampephilus robustus This mimicry reduces attacks on Dryocopus galeatusfrom other animals. Scientists had falsely believed that D. galeatus was a close cousin of the other two species, because of the visual similarity, and because the three species live in the same habitat and eat similar food. Batesian mimicry also occurs in the plant kingdom, such as the chameleon vine, which adapts its leaf shape and colour to match that of the plant it is climbing, such that its edible leaves appear to be the less desirable leaves of its host.
Müllerian mimicry, named for the German naturalist Fritz Müller, describes a situation where two or more species have similar warning or aposematic signals and both share genuine anti-predation attributes (e.g. being unpalatable). At first, Bates could not explain why this should be so—if both were harmful why did one need to mimic another? Müller put forward the first explanation for this phenomenon: if a common predator confuses two species, individuals in both those species are more likely to survive. This type of mimicry is unique in several respects. Firstly, both the mimic and the model benefit from the interaction, which could thus be classified as mutualism in this respect. The signal receiver is also advantaged by this system, despite being deceived about species identity, as it avoids potentially harmful encounters. The usually clear distinction between mimic and model is also blurred. Where one species is scarce and another abundant, the rare species can be said to be the mimic. When both are present in similar numbers, however, it is more realistic to speak of each as a co-mimic than of distinct 'mimic' and 'model' species, as their warning signals tend to converge. Also, the two species may exist on a continuum from harmless to highly noxious, so Batesian mimicry grades smoothly into Müllerian convergence.
The monarch butterfly (Danaus plexippus) is a member of a Müllerian complex with the viceroy butterfly (Limenitis archippus), sharing coloration patterns and display behaviour. The viceroy has subspecies with somewhat different coloration, each closely matching the local Danaus species. For example, in Florida, the pairing is of the viceroy and the queen butterfly, whereas in Mexico the viceroy resembles the soldier butterfly. The viceroy is thus involved in three different Müllerian pairs. This example was long believed to be Batesian, with the viceroy mimicking the monarch, but the viceroy is actually the more unpalatable species. The genus Morpho is palatable, but some species (such as M. amathonte) are strong fliers; birds – even species that specialize in catching butterflies on the wing – find it hard to catch them. The conspicuous blue coloration shared by most Morpho species may be Müllerian, or may be "pursuit aposematism". heliconiines]] Dryas iuliamillipedes enera Apheloria and Brachoria (Xystodesmidae) form a Müllerian mimicry ring in the eastern United States, in which unrelated polymorphic species converge on similar colour patterns where their range overlaps.
Emsleyan or Mertensian mimicry describes the unusual case where a deadly prey mimics a less dangerous species.
Some harmless milk snake (Lampropeltis triangulum) subspecies, the moderately toxic false coral snakes (genus Erythrolamprus), and the deadly coral snakes (genus Micrurus) all have a red background color with black and white / yellow rings. In this system, both the milk snakes and the deadly coral snakes are mimics, whereas the false coral snakes are the model. It has also been suggested that this system could be an instance of pseudomimicry, the similar colour patterns having evolved independently in similar habitats.
Vavilovian mimicry is found in weeds that come to share characteristics with a domesticated plant through artificial selection. It is named after Russian botanist and geneticist Nikolai Vavilov. Selection against the weed may occur either by manually killing the weed, or by separating its seeds from those of the crop by winnowing.
Vavilovian mimicry presents an illustration of unintentional (or rather 'anti-intentional') selection by man. Weeders do not want to select weeds and their seeds that look increasingly like cultivated plants, yet there is no other option. For example, early barnyard grass, Echinochloa oryzoides, is a weed in rice fields and looks similar to rice; its seeds are often mixed in rice and have become difficult to separate through Vavilovian mimicry. Vavilovian mimics may eventually be domesticated themselves, as in the case of rye in wheat; Vavilov called these weed-crops secondary crops.
Vavilovian mimicry can be classified as defensive mimicry, in that the weed mimics a protected species. This bears strong similarity to Batesian mimicry in that the weed does not share the properties that give the model its protection, and both the model and the dupe (in this case people) are harmed by its presence. There are some key differences, though; in Batesian mimicry, the model and signal receiver are enemies (the predator would eat the protected species if it could), whereas here the crop and its human growers are in a mutualistic relationship: the crop benefits from being dispersed and protected by people, despite being eaten by them. In fact, the crop's only "protection" relevant here is its usefulness to humans. Secondly, the weed is not eaten, but simply destroyed. The only motivation for killing the weed is its effect on crop yields. Finally, this type of mimicry does not occur in ecosystems unaltered by humans.
Gilbertian mimicry involves only two species.
Gilbertian mimicry occurs in the genus Passiflora. The leaves of this plant contain toxins that deter herbivorous animals. However, some Heliconius butterfly larvae have evolved enzymes that break down these toxins, allowing them to specialize on this genus. This has created further selection pressure on the host plants, which have evolved stipules that mimic mature Heliconius eggs near the point of hatching. These butterflies tend to avoid laying eggs near existing ones, which helps avoid exploitative intraspecific competition between caterpillars — those that lay on vacant leaves provide their offspring with a greater chance of survival. Most Heliconius larvae are cannibalistic, meaning that on leaves older eggs hatch first and eat the new arrivals. Thus, it seems that such plants have evolved egg dummies under selection pressure from these grazing herbivore enemies. In addition, the decoy eggs are also nectaries, attracting predators of the caterpillars such as ants and wasps as a further defence.
Browerian mimicry, named after Lincoln P. Brower and Jane Van Zandt Brower, is a postulated form of automimicry; where the model belongs to the same species as the mimic. This is the analogue of Batesian mimicry within a single species, and occurs when there is a palatability spectrum within a population. Examples include the monarch and the queen from the subfamily Danainae, which feed on milkweed species of varying toxicity. These species store toxins from its host plant, which are maintained even in the adult (imago) form. As levels of toxin vary depending on diet during the larval stage, some individuals are more toxic than others. Less palatable organisms, therefore, mimic more dangerous individuals, with their likeness already perfected.
This is not always the case, however.
Aggressive mimicry is found in predators or parasites that share some of the characteristics of a harmless species, allowing them to avoid detection by their prey or host; this can be compared with the story of the wolf in sheep's clothing as long as it is understood that no conscious deceptive intent is involved. The mimic may resemble the prey or host itself, or another organism that is either neutral or beneficial to the signal receiver. In this class of mimicry, the model may be affected negatively, positively or not at all. Just as parasites can be treated as a form of predator, host-parasite mimicry is treated here as a subclass of aggressive mimicry.
The mimic may have a particular significance for duped prey.
Another case is where males are lured towards what seems to be a sexually receptive female. The model in this situation is the same species as the dupe. Beginning in the 1960s, James E. Lloyd's investigation of female fireflies of the genus Photuris revealed they emit the same light signals that females of the genus Photinus use as a mating signal. Further research showed male fireflies from several different genera are attracted to these "femmes fatales", and are subsequently captured and eaten. Female signals are based on that received from the male, each female having a repertoire of signals matching the delay and duration of the female of the corresponding species. This mimicry may have evolved from non-mating signals that have become modified for predation.
The listrosceline katydid Chlorobalius leucoviridis of inland Australia is capable of attracting male cicadas of the tribe Cicadettini by imitating the species-specific reply clicks of sexually receptive female cicadas. This example of acoustic aggressive mimicry is similar to the Photuris firefly case in that the predator's mimicry is remarkably versatile – playback experiments show that C. leucoviridis is able to attract males of many cicada species, including cicadettine cicadas from other continents, even though cicada mating signals are species-specific.
Luring is not a necessary condition however, as the predator still has a significant advantage simply by not being identified as such.
A case of the latter situation is a species of cleaner fish and its mimic, though in this example the model is greatly disadvantaged by the presence of the mimic. Cleaner fish are the allies of many other species, which allow them to eat their parasites and dead skin. Some allow the cleaner to venture inside their body to hunt these parasites. However, one species of cleaner, the bluestreak cleaner wrasse (Labroides dimidiatus), is the unknowing model of a mimetic species, the sabre-toothed blenny (Aspidontus taeniatus). This wrasse resides in coral reefs in the Indian and the Pacific Oceans, and is recognized by other fishes that then let it clean them. Its imposter, a species of blenny, lives in the Indian Ocean—and not only looks like it in terms of size and coloration, but even mimics the cleaner's "dance". Having fooled its prey into letting its guard down, it then bites it, tearing off a piece of its fin before fleeing. Fish grazed on in this fashion soon learn to distinguish mimic from model, but because the similarity is close between the two they become much more cautious of the model as well, so both are affected. Due to victims' ability to discriminate between foe and helper, the blennies have evolved close similarity, right down to the regional level.
Another interesting example that does not involve any luring is the zone-tailed hawk, which resembles the turkey vulture. It flies amongst the vultures, suddenly breaking from the formation and ambushing its prey. Here the hawk's presence is of no evident significance to the vultures, affecting them neither negatively or positively.
Parasites can also be aggressive mimics, though the situation is somewhat different from those outlined previously.
In an unusual case, planidium larvae of some beetles of the genus Meloe form a group and produce a pheromone that mimics the sex attractant of its host bee species. When a male bee arrives and attempts to mate with the mass of larvae, they climb onto his abdomen. From there, they transfer to a female bee, and from there to the bee nest to parasitize the bee larvae.
Host-parasite mimicry is a two species system where a parasite mimics its own host.
Reproductive mimicry occurs when the actions of the dupe directly aid in the mimic's reproduction. This is common in plants with deceptive flowers that do not provide the reward they seem to offer and it may occur in Papua New Guinea fireflies, in which the signal of Pteroptyx effulgens is used by P. tarsalis to form aggregations to attract females. Other forms of mimicry have a reproductive component, such as Vavilovian mimicry involving seeds, vocal mimicry in birds, and aggressive and Batesian mimicry in brood parasite-host systems.
Bakerian mimicry, named after Herbert G. Baker, is a form of automimicry where female flowers mimic male flowers of their own species, cheating pollinators out of a reward. This reproductive mimicry may not be readily apparent as members of the same species may still exhibit some degree of sexual dimorphism. It is common in many species of Caricaceae.
Like Bakerian mimicry, Dodsonian mimicry is a form of reproductive floral mimicry, but the model belongs to a different species than the mimic.
Pseudocopulation occurs when a flower mimics a female of a certain insect species, inducing the males to try to copulate with the flower. This is much like the aggressive mimicry in fireflies described previously, but with a more benign outcome for the pollinator. This form of mimicry has been called Pouyannian mimicry, after Maurice-Alexandre Pouyanne, who first described the phenomenon.Un%20curieux%20cas%20de]]20]]pollinia stigma touch and olfaction that are most important.
Inter-sexual mimicry occurs when individuals of one sex in a species mimic members of the opposite sex to facilitate sneak mating. An example is the three male forms of the marine isopod Paracerceis sculpta. Alpha males are the largest and guard a harem of females. Beta males mimic females and manage to enter the harem of females without being detected by the alpha males allowing them to mate. Gamma males are the smallest males and mimic juveniles. This also allows them to mate with the females without the alpha males detecting them. Similarly, among common side-blotched lizards, some males mimic the yellow throat coloration and even mating rejection behaviour of the other sex to sneak matings with guarded females. These males look and behave like unreceptive females. This strategy is effective against "usurper" males with orange throats, but ineffective against blue throated "guarder" males, which chase them away. Female spotted hyenas have pseudo-penises that make them look like males.
Automimicry or intraspecific mimicry occurs within a single species.
Some writers use the term "automimicry" when the mimic imitates other morphs within the same species.
Many species of insects are toxic or distasteful when they have fed on certain plants that contain chemicals of particular classes, but not when they have fed on plants that lack those chemicals.
Some species of caterpillar, such as many hawkmoths (Sphingidae), have eyespots on their anterior abdominal segments. When alarmed, they retract the head and the thoracic segments into the body, leaving the apparently threatening large eyes at the front of the visible part of the body.
Many insects have filamentous "tails" at the ends of their wings and patterns of markings on the wings themselves.
Some forms of mimicry do not fit easily within the classification given above. Floral mimicry is induced by the discomycete fungus Monilinia vaccinii-corymbosi. In this unusual case, a fungal plant pathogen infects leaves of blueberries, causing them to secrete sugars, in effect mimicking the nectar of flowers. To the naked eye the leaves do not look like flowers, yet they still attract pollinating insects like bees using an ultraviolet signal. This case is unusual, in that the fungus benefits from the deception but it is the leaves that act as mimics, being harmed in the process. It is similar to host-parasite mimicry, but the host does not receive the signal. It has a little in common with automimicry, but the plant does not benefit from the mimicry, and the action of the pathogen is required to produce it.
It is widely accepted that mimicry evolves as a positive adaptation. The lepidopterist and novelist Vladimir Nabokov however argued that although natural selection might stabilize a "mimic" form, it would not be necessary to create it.
The most widely accepted model used to explain the evolution of mimicry in butterflies is the two-step hypothesis.
Some mimicry is imperfect.
Convergent evolution is an alternative explanation for why organisms such as coral reef fish and benthic marine invertebrates such as sponges and nudibranchs have come to resemble each other.