Automimicry

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Eyespots of foureye butterflyfish (Chaetodon capistratus) mimic its own eyes, which are camouflaged with a disruptive eye mask, deflecting attacks from the vulnerable head. Chaetodon capistratus2.jpg
Eyespots of foureye butterflyfish (Chaetodon capistratus) mimic its own eyes, which are camouflaged with a disruptive eye mask, deflecting attacks from the vulnerable head.

In zoology, automimicry, Browerian mimicry, or intraspecific mimicry, is a form of mimicry in which the same species of animal is imitated. There are two different forms.

Contents

In one form, first described by Lincoln Brower in 1967, weakly-defended members of a species with warning coloration are parasitic on more strongly-defended members of their species, mimicking them to provide the negative reinforcement learning required for warning signals to function. The mechanism, analogous to Batesian mimicry, is found in insects such as the monarch butterfly.

In another form, first noted by Edward B. Poulton in 1890, a less vulnerable part of an animal's body resembles a more vulnerable part, for example with deceptive eyespots or a false head that deflects attacks away from the real head, providing an immediate selective advantage. The mechanism is found in both vertebrates such as fishes and snakes, and insects such as hairstreak butterflies.

Automimicry has sometimes been put to military use. The A-10 Thunderbolt (Warthog) was often painted with a false canopy on its underside, imitating itself, while the armoured recovery vehicle variant of the Churchill tank had a dummy gun, imitating an armed variant of the same tank.

Mimicry of distasteful members of the same species

Automimicry was first reported by the ecologist Lincoln Brower and colleagues, who found that monarch butterflies reared on cabbage were palatable to blue jays. However, monarchs raised on their natural host plant, milkweed, were noxious to jays - in fact, jays that ingested them vomited. [1] [2] Subsequently, Brower proposed the hypothesis of automimicry involving a polymorphism or spectrum of palatability: some individuals might be defended, and others palatable. [3]

It turns out that many species of insects are toxic or distasteful when they have fed on plants that contain chemicals of particular classes, but not when they have fed on plants that lack those chemicals. For instance, some milkweed butterflies feed on milkweeds ( Asclepias ) which contain the cardiac glycoside oleandrin; this makes them poisonous to most predators. These insects are often aposematically coloured and patterned. When feeding on innocuous plants, they are harmless and nutritious, but a bird that has sampled a toxic specimen even once is unlikely to risk tasting harmless specimens with the same aposematic coloration. [2] [4] Such acquired toxicity is not limited to insects: many groups of animals have since been shown to obtain toxic compounds through their diets, making automimicry potentially widespread. Even if toxic compounds are produced by metabolic processes with an animal, there may still be variability in the amount that animals invest in them, so scope for automimicry remains even when dietary plasticity is not involved. Whatever the mechanism, palatability may vary with age, sex, or how recently they used their supply of toxin. [2]

If insect-eating birds, like this wagtail eating a moth, tend to avoid, or to taste and spit out, toxic insects, then mimicry of distasteful forms by harmless morphs of the same species should be favoured. Motacilla cinerea (eating moth).JPG
If insect-eating birds, like this wagtail eating a moth, tend to avoid, or to taste and spit out, toxic insects, then mimicry of distasteful forms by harmless morphs of the same species should be favoured.

The existence of automimicry in the form of non-toxic mimics of toxic members of the same species (analogous to Batesian mimicry [5] ) poses two challenges to evolutionary theory: how can automimicry be maintained, and how can it evolve? For the first question, as long as prey of the species are, on average, unprofitable for predators to attack, automimicry can persist. If this condition is not met, then the population of the species rapidly crashes. [2] The second question is more difficult, and can also be rephrased as being about the mechanisms that keep warning signals honest. If signals were not honest, they would not be evolutionarily stable. If costs of using toxins for defence affects members of a species, then cheats might always have higher fitness than honest signallers defended by costly toxins. A variety of hypotheses have been put forth to explain signal honesty in aposematic species. [6] First, toxins may not be costly. There is evidence that in some cases there is no cost, and that toxic compounds may actually be beneficial for purposes other than defence. If so, then automimics may simply be unlucky enough not to have gathered enough toxins from their environment. [7] A second hypothesis for signal honesty is that there may be frequency-dependent advantages to automimicry. If predators switch between host plants that provide toxins and plants that do not, depending on the abundance of larvae on each type, then automimicry of toxic larvae by non-toxic larvae may be maintained in a balanced polymorphism. [8] [9] A third hypothesis is that automimics are more likely to die or to be injured by a predator's attack. If predators carefully sample their prey and spit out any that taste bad before doing significant damage ("go-slow" behaviour), then honest signallers would have an advantage over automimics that cheat. [10]

False head

Many blue butterflies (Lycaenidae) such as this gray hairstreak (Strymon melinus) have a false head at the rear, held upwards at rest, deflecting attacks from the actual head. Gray Hairstreak (One more time...) (6222138633).jpg
Many blue butterflies (Lycaenidae) such as this gray hairstreak ( Strymon melinus ) have a false head at the rear, held upwards at rest, deflecting attacks from the actual head.

Many insects have filamentous "tails" at the ends of their wings and patterns of markings on the wings themselves. These combine to create a "false head". This misdirects predators such as birds and jumping spiders (Salticidae). Spectacular examples occur in the hairstreak butterflies; when perching on a twig or flower, they commonly do so upside down and shift their rear wings repeatedly, causing antenna-like movements of the "tails" on their wings. Studies of rear-wing damage support the hypothesis that this strategy is effective in deflecting attacks from the insect's head. [11] [12] [13] [14]

Natural selection in favour of features that deflect predators' attacks is straightforward to explain: variants of patterns that more effectively deflect attack are favoured, since animals with ineffective variants are likely to be killed. Naturalists [lower-alpha 1] since Edward B. Poulton in his 1890 book The Colours of Animals [15] have noted that butterflies with eyespots or other false head markings can be expected to escape with minor wing damage while the predator gets only "a mouthful of hindwing" instead of an insect meal. [12] In Poulton's words:

Each hind wing in these [hairstreak] butterflies is furnished with a 'tail', which in certain species is long, thin, and apparently knobbed at the end. When the butterfly is resting on a flower the wings are closed and the hind wings are kept in constant motion ... This movement, together with their appearance, causes the 'tails' to bear the strongest likeness to the antennae of a butterfly; the real antennae being held [downwards] so as not to attract attention. Close to the base of the supposed antennae an eye-like mark, in the most appropriate position, exists in many species. The effect of the marking and movement is to produce the deceptive appearance of a head at the wrong end of the body. The body is short and does not extend as far as the supposed head, so that the insect is uninjured when it is seized. [15]

Pygmy owl (Glaucidium californicum) showing eyespots behind head Glaucidium californicum Verdi Sierra Pines 2 (cropped).jpg
Pygmy owl ( Glaucidium californicum ) showing eyespots behind head

A 1981 experiment confirmed the expected correlation between deceptiveness and survival in butterflies. [12]

Among vertebrates, snakes such as the rubber boa and the coral snake coil up and hide their head, instead displaying their tail as a false head. [16] Some fishes such as the foureye butterflyfish have eyespots near their tails, and when mildly alarmed swim slowly backwards, presenting the tail as a head; however, various hypotheses for the function of such eyespots have been proposed. [17] Several species of pygmy owl bear false eyes (ocelli) on the back of the head, misleading predators into reacting as though they were the subject of an aggressive stare. [18]

Military usage

Automimicry has sometimes been used in military vehicles and aircraft. Among vehicles, specialised variants such as the British Second World War Churchill armoured recovery vehicle had no room for an actual gun, but was fitted with a dummy weapon, imitating the armed version of the same tank, to give it some protection. [19]

The ground attack A-10 Thunderbolt (Warthog) was sometimes painted with a camouflage scheme that included both disruptive coloration and automimicry in the form of a false canopy on the underside. This was intended to confuse the enemy about the aircraft's attitude and likely direction of travel. [20] [21]

Notes

  1. ↑ Including Swynnerton, 1926, and Blest, 1957. [12]

Related Research Articles

<span class="mw-page-title-main">Butterfly</span> Group of insects in the order Lepidoptera

Butterflies (Rhopalocera) are insects that have large, often brightly coloured wings, and a conspicuous, fluttering flight. The group comprises the superfamilies Hedyloidea and Papilionoidea. The oldest butterfly fossils have been dated to the Paleocene, about 56 million years ago, though they may have originated earlier.

<span class="mw-page-title-main">Mimicry</span> Imitation of another species for selective advantage

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 anti-predator adaptation. Mimicry evolves if a receiver perceives the similarity between a mimic and a model 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 and butterflies, 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 Müllerian mimicry rings, all resembling each other. Mimicry between prey species and their predators often involves three or more species.

<span class="mw-page-title-main">Batesian mimicry</span> Bluffing imitation of a strongly defended species

Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, after his work on butterflies in the rainforests of Brazil.

<span class="mw-page-title-main">Viceroy (butterfly)</span> Species of butterfly

The viceroy is a North American butterfly. It was long thought to be a Batesian mimic of the monarch butterfly, but since the viceroy is also distasteful to predators, it is now considered a Müllerian mimic instead.

<span class="mw-page-title-main">Owl butterfly</span> Members of brush-footed butterfly genus Caligo

The owl butterflies are species of the genus Caligo and are known for their huge eyespots, which resemble owls' eyes. They are found in the rainforests and secondary forests of Mexico, Central and South America.

<span class="mw-page-title-main">Müllerian mimicry</span> Mutually beneficial mimicry of strongly defended species

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. The benefit to Müllerian mimics is that predators only need one unpleasant encounter with one member of a set of Müllerian mimics, and thereafter avoid all similar coloration, whether or not it belongs to the same species as the initial encounter. It is named after the German naturalist Fritz Müller, who first proposed the concept in 1878, supporting his theory with the first mathematical model of frequency-dependent selection, one of the first such models anywhere in biology.

<span class="mw-page-title-main">Aposematism</span> Honest signalling of an animals powerful defences

Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defenses which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or smell, sharp spines, or aggressive nature. These advertising signals may take the form of conspicuous coloration, sounds, odours, or other perceivable characteristics. Aposematic signals are beneficial for both predator and prey, since both avoid potential harm.

<span class="mw-page-title-main">Ant mimicry</span> Animals that resemble ants

Ant mimicry or myrmecomorphy is mimicry of ants by other organisms. Ants are abundant all over the world, and potential predators that rely on vision to identify their prey, such as birds and wasps, normally avoid them, because they are either unpalatable or aggressive. Spiders are the most common ant mimics. Additionally, some arthropods mimic ants to escape predation, while others mimic ants anatomically and behaviourally to hunt ants in aggressive mimicry. Ant mimicry has existed almost as long as ants themselves; the earliest ant mimics in the fossil record appear in the mid Cretaceous alongside the earliest ants. Indeed one of the earliest, Burmomyrma, was initially classified as an ant.

<span class="mw-page-title-main">Eyespot (mimicry)</span> Eye-like marking used for mimicry or distraction

An eyespot is an eye-like marking. They are found in butterflies, reptiles, cats, birds and fish.

<span class="mw-page-title-main">Animal coloration</span> General appearance of an animal

Animal colouration is the general appearance of an animal resulting from the reflection or emission of light from its surfaces. Some animals are brightly coloured, while others are hard to see. In some species, such as the peafowl, the male has strong patterns, conspicuous colours and is iridescent, while the female is far less visible.

<span class="mw-page-title-main">Emsleyan mimicry</span> Mimicry of a less deadly species

Emsleyan mimicry, also called Mertensian mimicry, describes an unusual type of mimicry where a deadly prey mimics a less dangerous species.

G.D. Hale Carpenter MBE was a British entomologist and medical doctor. He worked first at the London School of Hygiene and Tropical Medicine, and in Uganda, on tse-tse flies and sleeping sickness. His main work in zoology was on mimicry in butterflies, an interest he developed in Uganda and Tanganyika. He succeeded E.B. Poulton as Hope Professor of Zoology at Oxford University from 1933 to 1948.

Insects have a wide variety of predators, including birds, reptiles, amphibians, mammals, carnivorous plants, and other arthropods. The great majority (80–99.99%) of individuals born do not survive to reproductive age, with perhaps 50% of this mortality rate attributed to predation. In order to deal with this ongoing escapist battle, insects have evolved a wide range of defense mechanisms. The only restraint on these adaptations is that their cost, in terms of time and energy, does not exceed the benefit that they provide to the organism. The further that a feature tips the balance towards beneficial, the more likely that selection will act upon the trait, passing it down to further generations. The opposite also holds true; defenses that are too costly will have a little chance of being passed down. Examples of defenses that have withstood the test of time include hiding, escape by flight or running, and firmly holding ground to fight as well as producing chemicals and social structures that help prevent predation.

<i>Adaptive Coloration in Animals</i> 1940 textbook on camouflage, mimicry and aposematism by Hugh Cott

Adaptive Coloration in Animals is a 500-page textbook about camouflage, warning coloration and mimicry by the Cambridge zoologist Hugh Cott, first published during the Second World War in 1940; the book sold widely and made him famous.

<span class="mw-page-title-main">Mimicry in plants</span>

In evolutionary biology, mimicry in plants is where a plant organism evolves to resemble another organism physically or chemically, increasing the mimic's Darwinian fitness. Mimicry in plants has been studied far less than mimicry in animals, with fewer documented cases and peer-reviewed studies. However, it may provide protection against herbivory, or may deceptively encourage mutualists, like pollinators, to provide a service without offering a reward in return.

<span class="mw-page-title-main">Deimatic behaviour</span> Bluffing display of an animal used to startle or scare a predator

Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey animal an opportunity to escape. The term deimatic or dymantic originates from the Greek δειματόω (deimatóo), meaning "to frighten".

Deception in animals is the transmission of misinformation by one animal to another, of the same or different species, in a way that propagates beliefs that are not true.

<span class="mw-page-title-main">Coloration evidence for natural selection</span> Early evidence for Darwinism from animal coloration

Animal coloration provided important early evidence for evolution by natural selection, at a time when little direct evidence was available. Three major functions of coloration were discovered in the second half of the 19th century, and subsequently used as evidence of selection: camouflage ; mimicry, both Batesian and Müllerian; and aposematism.

Locomotor mimicry is a subtype of Batesian mimicry in which animals avoid predation by mimicking the movements of another species phylogenetically separated. This can be in the form of mimicking a less desirable species or by mimicking the predator itself. Animals can show similarity in swimming, walking, or flying of their model animals.

In evolutionary biology, mimicry in vertebrates is mimicry by a vertebrate of some model, deceiving some other animal, the dupe. Mimicry differs from camouflage as it is meant to be seen, while animals use camouflage to remain hidden. Visual, olfactory, auditory, biochemical, and behavioral modalities of mimicry have been documented in vertebrates.

References

  1. ↑ Brower, Lincoln Pierson; Cook, Laurence M.; Croze, Harvey J. (March 1967). "Predator Responses to Artificial Batesian Mimics Released in a Neotropical Environment". Evolution. 21 (1): 11–23. doi:10.2307/2406736. JSTOR   2406736. PMID   28556119.
  2. 1 2 3 4 Ruxton, Graeme D.; Sherratt, T. N.; Speed, M. P. (2004). Avoiding Attack: the Evolutionary Ecology of Crypsis, Warning Signals, and Mimicry. Oxford University Press. pp. 176–182. ISBN   9780198528593.
  3. ↑ Brower, Lincoln Pierson; Ryerson, William N.; Coppinger, Lorna L.; Glazier, Susan C. (27 September 1968). "Ecological Chemistry and the Palatability Spectrum". Science. 161 (3848): 1349–1351. Bibcode:1968Sci...161.1349B. doi:10.1126/science.161.3848.1349. PMID   17831347. S2CID   45185502.
  4. ↑ Svennungsen, Thomas Owens; Holen, Øistein Haugsten (2007). "The evolutionary stability of automimicry". Proc. R. Soc. B. 274 (1621): 2055–2063. doi:10.1098/rspb.2007.0456. PMC   2275178 . PMID   17567561.
  5. ↑ Brower, Lincoln P.; Pough, F. Harvey; Meck, H. R. (August 1970). "Theoretical Investigations of Automimicry, I. Single Trial Learning". Proceedings of the National Academy of Sciences. 66 (4): 1059–1066. Bibcode:1970PNAS...66.1059B. doi: 10.1073/pnas.66.4.1059 . PMC   335786 . PMID   16591844.
  6. ↑ Summers, K.; Speed, M. P.; Blount, J. D.; Stuckert, A. M. M. (2015). "Are aposematic signals honest? A review". Journal of Evolutionary Biology. 28 (9): 1583–1599. doi: 10.1111/jeb.12676 . PMID   26079980. S2CID   9920426.
  7. ↑ Leimar, Olof; Enquist, Magnus; Sillen-Tullberg, Birgitta (1 January 1986). "Evolutionary Stability of Aposematic Coloration and Prey Unprofitability: A Theoretical Analysis". The American Naturalist. 128 (4): 469–490. doi:10.1086/284581. JSTOR   2461331. S2CID   84450857.
  8. ↑ Ruxton, Graeme D.; Speed, M. P. (2006). "How can automimicry persist when predators can preferentially consume undefended mimics?". Proceedings of the Royal Society B: Biological Sciences. 273 (1584): 373–378. doi:10.1098/rspb.2005.3238. PMC   1560041 . PMID   16543181.
  9. ↑ Brower, Lincoln P.; Pough, F. Harvey; Meck, H. R. (15 August 1970). "Theoretical Investigations of Automimicry, I. Single Trial Learning". Proceedings of the National Academy of Sciences of the United States of America. 66 (4): 1059–1066. Bibcode:1970PNAS...66.1059B. doi: 10.1073/pnas.66.4.1059 . JSTOR   59920. PMC   335786 . PMID   16591844.
  10. ↑ Guilford, Tim (October 1994). ""Go-slow" Signalling and the Problem of Automimicry". Journal of Theoretical Biology. 170 (3): 311–316. Bibcode:1994JThBi.170..311G. doi:10.1006/jtbi.1994.1192.
  11. ↑ Sourakov, Andrei (2013). "Two heads are better than one: false head allows Calycopis cecrops (Lycaenidae) to escape predation by a Jumping Spider, Phidippus pulcherrimus (Salticidae)". Journal of Natural History. 47 (15–16): 1047–1054. doi:10.1080/00222933.2012.759288. S2CID   84454608.
  12. 1 2 3 4 Robbins, Robert K. (November 1981). "The "False Head" Hypothesis: Predation and Wing Pattern Variation of Lycaenid Butterflies". The American Naturalist. 118 (5): 770–775. doi:10.1086/283868. S2CID   34146954.
  13. ↑ López-Palafox, Tania; Cordero, Carlos (2017-06-22). "Two-headed butterfly vs. mantis: do false antennae matter?". PeerJ. 5: e3493. doi: 10.7717/peerj.3493 . PMC   5483043 . PMID   28652941.
  14. ↑ Cordero, Carlos; López-Palafox, Tania G. (August 2015). "The movement of 'false antennae' in butterflies with 'false head' wing patterns". Current Zoology. 61 (4): 758–764. doi: 10.1093/czoolo/61.4.758 .
  15. 1 2 Poulton, Edward B. (1890). The Colours of Animals. Kegan Paul, Trench, Trübner. pp. 206–209.
  16. ↑ Graham, Sean P. (18 February 2018). American Snakes. JHU Press. p. 319. ISBN   978-1-4214-2360-9.
  17. ↑ Meadows, D. W. (11 February 1993). "Morphological variation in eyespots of the foureye butterflyfish (Chaetodon capistratus): Implications for eyespot function". Copeia. 1993 (1): 235–240. doi:10.2307/1446319. JSTOR   1446319.
  18. ↑ "Northern Pygmy Owl (Glaucidium californicum)". Owl Research Institute. Archived from the original on 28 December 2015. Retrieved 23 August 2015.
  19. ↑ Chamberlain, Peter; Ellis, Chris (1969). British and American Tanks of World War II. Arco Publishing. p. 70.
  20. ↑ Shaw, Robert (1985). Fighter combat: tactics and maneuvring . Naval Institute Press. p.  382. ISBN   0-87021-059-9.
  21. ↑ Neubeck, Ken (1999). A-10 Warthog Walk Around. Squadron/Signal Publications. pp. 72–77, 92. ISBN   0-89747-400-7.
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