Batesian mimicry
Encyclopedia
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...
, after his work in the rainforest
Rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
s of 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...
.
Batesian mimicry is the most commonly known and widely studied of mimicry complexes, such that the word mimicry is often treated as synonymous with Batesian mimicry. There are many other forms however, some very similar in principle, others far separated. Of note, it is often contrasted with Müllerian mimicry
Müllerian mimicry
Müllerian mimicry is a natural phenomenon when two or more harmful species, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals...
, a form of mutually beneficial convergence between two or more harmful species. However, because the mimic may have a degree of protection itself, the distinction is not absolute. It can also be contrasted with functionally different forms of mimicry. Perhaps the sharpest contrast here is with 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...
, where a predator or parasite mimics a harmless species, avoiding detection 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.
The organism imitating the protected species is referred to as the mimic, while the imitated organism is known as the model. The receiver mediating indirect interactions between these two parties is variously known as the signal receiver, dupe or operator. By parasitizing the 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"...
of the protected species, the Batesian mimic gains the same advantage, without having to go to the expense of arming themselves. The model, on the other hand, is disadvantaged, along with the dupe. If imposters appear in high numbers, positive experiences with the mimic may result in the model being treated as harmless. Additionally, in higher frequency there is a stronger selective advantage for the predator to distinguish mimic from model. For this reason, mimics are usually less numerous than models. However, some mimetic populations have evolved multiple forms (polymorphism
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
), enabling them to mimic several different models. This affords them greater protection, a concept in evolutionary biology known as frequency dependent selection
Frequency dependent selection
Frequency-dependent selection is the term given to an evolutionary process where the fitness of a phenotype is dependent on its frequency relative to other phenotypes in a given population. In positive frequency-dependent selection the fitness of a phenotype increases as it becomes more common...
.
Batesian mimicry need not involve visual mimicry, but can employ deception
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...
of 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, some moths mimic the ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
warning signals sent by unpalatable moths to bat predators, a case of auditory Batesian mimicry. A cocktail of deceptive signals may also be used. The distinction between Batesian mimicry and crypsis
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...
is clear: the mimic is noticed, but treated as something it is not. On the other hand, camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
d prey would often create the same effect by being invisible. While model and mimic are often from related taxa, mimicry of very distant relatives
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....
is also known. The majority of Batesian mimics are insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s.
Historical background
Henry Walter Bates (1825–1892) was an EnglishEngland
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
explorer-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...
who surveyed the Amazon Rainforest
Amazon Rainforest
The Amazon Rainforest , also known in English as Amazonia or the Amazon Jungle, is a moist broadleaf forest that covers most of the Amazon Basin of South America...
with Alfred Russel Wallace
Alfred Russel Wallace
Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
in 1848. While Wallace returned in 1852, Bates remained for over a decade. His field research included collecting almost a hundred species of butterflies from the families Ithomiinae and Heliconiinae
Heliconiinae
The Heliconiinae, commonly called heliconians or longwings, are a subfamily of the brush-footed butterflies . They can be divided into 45-50 genera and were sometimes treated as a separate family Heliconiidae within the Papilionoidea...
, as well as thousands of other insects specimens. In sorting these butterflies into similar groups based on appearance, inconsistencies began to arise. Some appeared superficially similar to others, even so much so that Bates could not tell some species apart based only on wing appearance. However, closer examination of less obvious morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
characters seemed to show that they were not even closely related. Shortly after his return to England he read a paper on his theory of mimicry at a meeting of the Linnean Society of London
Linnean Society of London
The Linnean Society of London is the world's premier society for the study and dissemination of taxonomy and natural history. It publishes a zoological journal, as well as botanical and biological journals...
on the 21st of November 1861, which was then published in 1862 as 'Contributions to an Insect Fauna of the Amazon Valley' in the Transactions of the Linnaean Society. He elaborated on his experiences further in The Naturalist on the River Amazons
The Naturalist on the River Amazons
The Naturalist on the River Amazons, subtitled A Record of the Adventures, Habits of Animals, Sketches of Brazilian and Indian Life, and Aspects of Nature under the Equator, during Eleven Years of Travel, is an 1863 book by the British naturalist Henry Walter Bates about his expedition to the...
. These new findings and speculations stimulated long lasting discussion and controversy, not limited to the scientific realm.
Bates put forward the hypothesis that the close resemblance between unrelated species was an antipredator adaptation. He noted that some species showed very striking coloration, and flew in a leisurely manner, almost as if taunting predators to eat them. He reasoned that these butterflies were unpalatable to birds and other insectivore
Insectivore
An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....
s, and were thus avoided by them. He extended this logic to forms that closely resembled such protected species, mimicking their warning coloration but not their toxicity.
This naturalistic
Naturalism (philosophy)
Naturalism commonly refers to the philosophical viewpoint that the natural universe and its natural laws and forces operate in the universe, and that nothing exists beyond the natural universe or, if it does, it does not affect the natural universe that we know...
explanation fitted well with the recent account 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...
by Alfred Russel Wallace and Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
, as outlined in his famous 1859 book The Origin of Species
The Origin of Species
Charles Darwin's On the Origin of Species, published on 24 November 1859, is a work of scientific literature which is considered to be the foundation of evolutionary biology. Its full title was On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the...
. Because this Darwinian
Darwinism
Darwinism is a set of movements and concepts related to ideas of transmutation of species or of evolution, including some ideas with no connection to the work of Charles Darwin....
explanation required no supernatural forces, it met with considerable criticism from anti-evolutionists
Objections to evolution
Objections to evolution have been raised since evolutionary ideas came to prominence in the 19th century. When Charles Darwin published his 1859 book On the Origin of Species, his theory of evolution by natural selection initially met opposition from scientists with different theories, but came to...
, both in academic circles and in the broader social realm
Social effect of evolutionary theory
The social effects of evolutionary thought have been considerable. As the scientific explanation of life's diversity has developed, it has often displaced alternative, sometimes very widely held, explanations. Because the theory of evolution includes an explanation of humanity's origins, it has...
. The term mimicry had only been used for people until about 1850, when the word took on a new life in its application to other life forms such as plants and animals. Just as Darwin was the first to put forward a comprehensive explanation for evolution, Bates was the first to elucidate this form of mimicry, and he is thus honored with the term Batesian mimicry. Although other forms have been discovered even in recent times, Batesian mimicry is one of the most commonly occurring and well understood. To many, the word Batesian mimicry and mimicry are treated as the same thing, however it should not be overlooked that Bates described several kinds himself.
Aposematism
Evolutionary arms race
In evolutionary biology, an evolutionary arms race is an evolutionary struggle between competing sets of co-evolving genes that develop adaptations and counter-adaptations against each other, resembling an arms race, which are also examples of positive feedback...
to develop protective adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
s. Some organisms have evolved to make detection
Prey detection
Prey detection is the process by which predators are able to detect and locate their prey via sensory signals. This article treats predation in its broadest sense, i.e. where one organism eats another.-Evolutionary struggle and prey defenses:...
less likely; this is known as camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
. Other organisms are not profitable for potential predators even if they do locate them. Some lizards, for example, will do 'pushups' if they are spotted, advertising to the predator just how strong and healthy they are - that pursuing them is just not energetically profitable. Still others however are harmful even if the predator can eat them, for example many plants and fungi contain deadly toxins and other chemicals, while certain snakes, wasps, and other animals are able to poison, injure, or otherwise harm many of the predators who would otherwise eat them. Such prey often send clear warning signals to their attackers, such as strong odors, bright colours and warning sounds. Note that the word 'prey' refers to any living organism subject to being eaten, whether animal, plant or anything else.
Use of such messages is known as 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...
. Aposematic prey need not display such signals all the time. It may be energetically costly for them to do so, and even if it is not, they may have other predators that can tolerate their defenses. In fact, even if all their predators will avoid them if adequately warned, there are still those predators that have not yet learned
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...
that they are dangerous. Short of instinctive programming to avoid the aposematic organism (which is seen occasionally), it is unlikely that any potential prey will be prepared to sacrificially educate its predator. Thus, a combination of camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
and its antithesis, aposematism, often occur.
However, once a predator has learned from harsh experience not to go after such prey, it will be likely to avoid anything that looks even remotely similar if it can. It is in this fashion that Batesian mimics have evolved. It is often misunderstood that such a mimic is somehow responsible itself for its mimetic characteristics. This is quite a serious misunderstanding, however. It is the duped predator that does the selecting, choosing to avoid those prey which look most like the aposematic model. In this way, the signal receiver directs the evolution of the mimic toward closer and closer similarity to the model.
Classification and comparisons
Batesian mimicry is a case of protective or defensive mimicry, where the mimic does best by avoiding confrontations with the signal receiver. It is a disjunct system, which means that all three parties are from a different species. Batesian mimicry stands in contrast to other forms such as aggressive mimicryAggressive 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...
, where the mimic profits from interactions with the signal receiver. One such case of this is in fireflies, where females of one species mimic the mating signals of another species, deceiving males to come close enough for them to eat. Mimicry need not involve a predator at all though. Such is the case in dispersal mimicry, where the mimic once again benefits from the encounter. For instance, some fungi have their spores dispersed by insects by smelling like carrion. In protective mimicry, the meeting between mimic and dupe is not such a fortuitous occasion for the mimic, and the signals it mimics tend to lower the probability of such an encounter.
One case somewhat similar to Batesian mimicry is that of mimetic weeds, which imitate agricultural crops. Once again, this is the result of the signal receiver's action, not a cunning ploy of the mimic. In weed, or Vavilovian mimicry
Vavilovian mimicry
Vavilovian mimicry is a form of mimicry in plants where a weed comes to share one or more characteristics with a domesticated plant through generations of artificial selection. It is named after Nikolai Vavilov, a prominent Russian plant geneticist who identified the centres of origin of...
, the weed does not profit from encounters with man or his winnowing machinery; at best the weed is left, at worst it is destroyed. Vavilovian mimicry is not a case of Batesian mimicry, however, because man and crop are not enemies. Indeed, the crops derive their protection from insects, weeds, and competition with other plants from their growers.
Another analogous case within a single species has been termed Browerian mimicry (after Lincoln P. Brower and Jane Van Zandt Brower). This is a case of bipolar (only two species involved) automimicry; the model is same species as its mimic. Equivalent to Batesian mimicry within a single species, it occurs when there is a palatability spectrum within a population of harmful prey. For example, Monarch Butterflies (Danaus plexippus) feed on milkweed species of varying toxicity. Some larvae will feed on more toxic plants, and store these toxins within themselves, while others will not. The less palatable caterpillars will thus profit from those that ingest high levels of toxic substances, just as other butterfly species benefit from mimicry of Monarchs.
Comparison with Müllerian mimicry
Müller came up with an explanation for this puzzle in 1878. Unlike in Batesian mimicry, the model is not being pirated by the mimic. In fact, the key here is that the model actually benefits from being mimicked, because it can share the troublesome burden of enlightening the predator of its harmful properties. In this cooperative enterprise, both parties benefit. It could thus be classified as a form of mutualism, an ecological relationship where two species gain mutual advantage from a biological interaction; in this case via the signal receiver.
In this account, it has been assumed that one species acts as a mimic and the other as a model. But which species should be designated each part? If two aposematic species that encounter the predator in equal number equally often come to mimic each other, it becomes completely arbitrary to call one a mimic and another a model. In fact, both can be said to be comimics, as the role of mimic and model is shared by both. Each species gains from the negative experiences of their common predator with the other. Another problem is that the predator isn't actually deceived regarding the harmful properties of the 'mimic', as both species are truly harmful. For these two reasons, some have suggested Müllerian mimicry is not mimicry at all, and have proposed terms such as Müllerian resemblance or Müllerian convergence. Looked at in another light however, it can still be seen as a form of deception in that the signal receiver treats the species it has not had an unpleasant experience with as if it were the model. This is a case of mistaken identity, although one that benefits the predator. Whether treated as mimicry or not, Müllerian convergences certainly break many of the assumptions that normally apply to mimicry complexes, and are quite the opposite of Batesian mimicry.
Imperfect Batesian mimicry
One of the most studied aspects of Batesian mimicry centers around the existence of imperfect or poor mimics, which do not exactly resemble their models. There are multiple theories behind why there are poor mimics, including that they are simply evolving toward perfection; that they may gain advantage from resembling multiple mimics at once; that humans may evaluate mimics in different ways than the actual predators; that mimics may confuse predators by resembling both model and nonmimic at the same time (satiric mimicry); that kin selection may enforce poor mimicry; that mimics may not gain enough by being perfect mimics to make it worth giving up other advantages like thermoregulation, or cryptic coloration. More than likely it is a combination of many of these factors under different circumstances.Acoustic mimicry
Though visual mimicry has been extensively researched, acoustic mimicry is also known, and occurs in a variety of species. Predators may identify their prey by sound as well as sight, and mimics have evolved that play tricks on the hearingHearing (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...
of those that would eat them.
One example is the use of ultrasonic resistance. Bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s rely heavily on echolocation
Animal echolocation
Echolocation, also called biosonar, is the biological sonar used by several kinds of animals.Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects...
to detect their prey, such that their auditory system might well be equivalent both in importance and perceptual nature to the human visual system
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
. Some potential prey are unpalatable to bats however, and produce an ultrasonic aposematic signal, the auditory equivalent of warning coloration. In response to echolocating red and big brown bats, tiger moths produce warning sounds. Bats learn to avoid the harmful moths, but due to their association of the warning signal with danger, they similarly avoid other species that produce such warning sounds as well. Results like these indicate acoustic mimicry complexes, both Batesian and Mullerian, may be widespread in the auditory world.
Further reading
Original paper by Bates. A shortened version is reprinted in Biological Journal of the Linnean Society (1981) 16: 41-54.- Cott, H.B. (1940) Adaptive Coloration in Animals. Methuen and Co, Ltd., London ISBN 0-416-30050-2 Provides many examples of Batesian Mimicry For a historical perspective.
- Wickler, W.Wolfgang WicklerWolfgang 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 0-07-070100-8 Especially the first two chapters. - Edmunds, M. 1974. Defence in Animals: A Survey of Anti-Predator Defences. Harlow, Essex & NY: Longman 357 p. ISBN 0-582-44132-3 Chapter 4 discusses this phenomenon. A detailed discussion of the different forms of mimicry.
- Ruxton, G. D.Graeme RuxtonGraeme 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 0-19-852860-4 Chapter 10 and 11 provide an up to date synopsis
External links
- Review of Contributions to an insect fauna of the Amazon valley by Charles Darwin The Complete Works of Charles Darwin OnlineThe Complete Works of Charles Darwin OnlineThe Complete Work of Charles Darwin Online is a freely-accessible website containing the complete print and manuscript works of Charles Darwin, as well as related supplementary material.- Overview :...
. - Biographical sketch of Bates, with picture