Examples:

Emsleyan/Mertensian

Emsleyan or Mertensian mimicry describes unusual cases where deadly prey mimic a less dangerous species. It was first proposed by Emsley as a possible answer for the problem of Coral Snake mimicry in the New World. It was elaborated on by the German biologist Wolfgang Wickler in a chapter of Mimicry in Plants and Animals, who named it after the German herpetologist Robert Mertens. Sheppard points out that Hecht and Marien put forward a similar hypothesis ten years earlier.

This scenario is a little more difficult to understand, as in other types of mimicry it is usually the most harmful species that is the model. But if a predator dies, it cannot learn to recognize a warning signal, e.g. bright colors in a certain pattern. In other words, there is no advantage in being aposematic for an organism that is likely to kill any predator it succeeds in poisoning; such an animal would rather profit from being camouflaged, to avoid attacks altogether. If, however, there is some other species that is harmful but not deadly as well as aposematic, the predator may learn to recognize its particular warning colors and avoid such animals. A deadly species will then profit by mimicking the less dangerous aposematic organism, if this results in less attacks than camouflage would.

The exception here, ignoring any chance of animals learning by watching a conspecific die (see Jouventin et al. for a discussion of observational learning and mimicry), is the possibility of not having to learn that it is harmful in the first place: instinctive genetic programming to be wary of certain signals. In this case, other organisms could benefit from this programming, and Batesian or Müllerian mimics of it could potentially evolve. In fact, it has been shown that some species do have an innate recognition of certain aposematic warnings. Hand-reared Turquoise-browed Motmots (Eumomota superciliosa), avian predators, instinctively avoid snakes with red and yellow rings. Other colors with the same pattern, and even red and yellow stripes with the same width as rings, were tolerated. However, models with red and yellow rings were feared, with the birds flying away and giving alarm calls in some cases. This provides one alternative explanation to Mertensian mimicry. See Greene and McDiarmid for a review of the subject.

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 rings. In this system, both the milk snakes and the deadly coral snakes are mimics, whereas the false coral snakes are the model.

Wasmannian

Mimetic weeds

Vavilovian mimicry presents an illustration of unintentional (or rather 'anti-intentional') selection by man. While some cases of artificial selection go in the direction desired, such as selective breeding, this case presents the opposite characteristics. Weeders do not want to select weeds that look increasingly like the cultivated plant, yet there is no other option. A similar problem in agriculture is pesticide. Vavilovian mimics may eventually be domesticated themselves, and Vavilov called these weeds-cum-crops secondary crops.

It 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 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.

One case is Echinochloa oryzoides, 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.

Protective egg decoys

This form of protective mimicry occurs in the genus Passiflora. The leaves of this plant contain toxins which deter herbivorous animals, however some Heliconius butterfly larvae have evolved enzymes which 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 each 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. Additionally, most Heliconius larvae are cannibalistic, meaning those leaves with older eggs will hatch first and eat the new arrivals. Thus, it seems such plants have evolved egg dummies due to these grazing herbivore enemies. The decoy eggs are also nectaries though, attracting predators of the caterpillars such as ants and wasps. The extent of their mimetic function is therefore slightly more difficult to assess.

The use of eggs is not essential to this system, only the species composition and protective function. Many other forms of mimicry also involve eggs, such as cuckoo eggs mimicking those of their host (the reverse of this situation), or plants seeds (often those with an elaiosome) being dispersed by ants, who treat them as they would their own eggs.

Protective mimicry within a species

Aggressive

The mimic may have a particular significance for duped prey. One such case is spiders, amongst which aggressive mimicry is quite common in both luring prey and stealthily approaching predators. One case is the Golden Orb Weaver (Nephila clavipes), which spins a conspicuous golden colored web in well-lit areas. Experiments show that bees are able to associate the webs with danger when the yellow pigment is not present, as occurs in less well-lit areas where the web is much harder to see. Other colors were also learned and avoided, but bees seemed least able to effectively associate yellow pigmented webs with danger. Yellow is the color of many nectar bearing flowers, however, so perhaps avoiding yellow is not worth while. Another form of mimicry is based not on color but pattern. Species such as Argiope argentata employ prominent patterns in the middle of their webs, such as zigzags. These may reflect ultraviolet light, and mimic the pattern seen in many flowers known as nectar guides. Spiders change their web day to day, which can be explained by bee's ability to remember web patterns. Bees are able to associate a certain pattern with a spatial location, meaning the spider must spin a new pattern regularly or suffer diminishing prey capture.

Another case is where males are lured towards what would seem to be a sexually receptive female; the model in this situation being 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.

Some carnivorous plants may also be able to increase their rate of capture through mimicry.

Luring is not a necessary condition however, as the predator will still have a significant advantage by simply not being identified as such. They may resemble a mutualistic symbiont or a species of little relevance to the prey.

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, shown to the left cleaning a grouper of the genus Epinephelus, resides in coral reefs in the Indian and the Pacific Oceans, and is recognized by other fishes who then allow it to 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 the scene. Fish grazed upon 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, such that both are affected. Due to victim's 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

Some of the predators described have a feature that draws prey, and parasites can also mimic their host's natural prey, but are eaten themselves, a pathway into their host. Leucochloridium, a genus of flatworm, matures in the digestive system of songbirds, their eggs then passing out of the bird via the feces. They are then taken up by Succinea, a terrestrial snail. The eggs develop in this intermediate host, and then must find of a suitable bird to mature in. As the host birds do not eat snails, so the sporocyst has another strategy to reach its host's intestine. They are brightly colored and move in a pulsating fashion. A sporocyst-sac pulsates in the snail's eye stalks, coming to resemble an irresistible meal for a songbird. In this way, it can bridge the gap between hosts, allowing it to complete its life cycle. A nematode (Myrmeconema neotropicum) changes the colour of the abdomen of workers of the canopy ant Cephalotes atratus to make it appear like the ripe fruits of Hyeronima alchorneoides. It also changes the behaviour of the ant so that the gaster (rear part) is held raised. This presumably increases the chances of the ant being eaten by birds. The droppings of birds are collected by other ants and fed to their brood, thereby helping to spread the nematode.

In an unusual case, planidium larvae of some beetles of the genus Meloe will form a group and produce a pheromone that mimics the sex attractant of its host bee species; when the male bee arrives and attempts to mate with the mass of larvae, they climb onto his abdomen, and from there 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. Cuckoos are a canonical example of brood parasitism, a form of kleptoparasitism where the mother has its offspring raised by another unwitting organism, cutting down the biological mother's parental investment in the process. The ability to lay eggs which mimic the host eggs is the key adaptation. The adaptation to different hosts is inherited through the female line in so-called gentes. Cases of intraspecific brood parasitism, where a female lays in conspecific's nest, as illustrated by the Goldeneye duck (Bucephala clangula), do not represent a case of mimicry.

Reproductive

Mimicry of flowers

Like Bakerian mimicry, Dodsonian mimicry is a form of reproductive floral mimicry, but the model belongs to a different species than the mimic. The name refers to Calaway H. Dodson. By providing similar sensory signals as the model flower, it can lure its pollinators. Like Bakerian mimics, no nectar is provided. Epidendrum ibaguense of the family Orchidaceae resembles flowers of Lantana camara and Asclepias curassavica, and is pollinated by Monarch Butterflies and perhaps hummingbirds. Similar cases are seen in some other species of the same family. The mimetic species may still have pollinators of its own though, for example a lamellicorn beetle which usually pollinates correspondingly colored Cistus flowers is also known to aid in pollination of Ophrys species that are normally pollinated by bees.

Pseudocopulation

Inter-sexual mimicry

Automimicry

Examples:

Other

Owl butterflies (genus Caligo) bear eye-spots on the underside of their wings; if turned upside-down, their undersides resemble 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 fooled. 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. Research suggests that eye-spots are not a form of mimicry and do not deter predators because they look like eyes. Rather the conspicuous contrast in the patterns on the wings deter predators.

Another case is floral mimicry induced by the discomycete fungus Monilinia vaccinii-corymbosi. In this unusual case, a fungal plant pathogen infects leaves of blueberries, causing them to secrete sugary substances including glucose and fructose, in effect mimicking the nectar of flowers. To the naked eye the leaves do not look like flowers, yet strangely they still attract pollinating insects like bees. As it turns out, the sweet secretions are not the only cues—the leaves also reflect ultraviolet, which is normally absorbed by the plant's leaves. Ultraviolet light is also employed by the host's flowers as a signal to insects, which have visual systems quite capable of picking up this low wavelength (300–400 nm) radiation. The fungus is then transferred to the ovaries of the flower where it produces mummified, inedible berries, which overwinter before infecting new plants. This case is unusual in that the fungus benefits from the deception, but it is the leaves which act as mimics, being harmed in the process. It bears similarity to host-parasite mimicry, but the host does not receive the signal. It also 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.

Evolution

The most widely accepted model used to explain the evolution of mimicry in butterflies is the two-step hypothesis. In this model the first step involves mutation in modifier genes that regulate a complex cluster of linked genes associated with large changes in morphology. The second step consists of selections on genes with smaller phenotypic effects and this leading to increasing closeness of resemblance. This model is supported by empirical evidence that suggests that there are only a few single point mutations that cause large phenotypic effects while there are numerous others that produce smaller effects. Some regulatory elements are now known to be involved in a supergene that is involved in the development of butterfly color patterns. Computational simulations of population genetics have also supported this idea.

See also

Similar terms

References

Further reading

External links

* Category:Polymorphism