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Cleaning symbiosis is a mutually beneficial association between individuals of two species, where one (the cleaner) removes and eats parasites and other materials from the surface of the other (the client). Cleaning symbiosis is well-known among marine fish, where some small species of
cleaner fish Cleaner fish are fish that show a specialist feeding strategy by providing a service to other species, referred to as clients, by removing dead skin, ectoparasites, and infected tissue from the surface or gill chambers. This example of cleaning ...
, notably
wrasse The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 81 genera, which are divided into 9 subgroups or tribes. They are typically small, most of them l ...
s but also species in other genera, are specialised to feed almost exclusively by cleaning larger fish and other marine animals. Other cleaning symbioses exist between birds and mammals, and in other groups. Cleaning behaviour was first described by the Greek historian
Herodotus Herodotus ( ; grc, , }; BC) was an ancient Greek historian and geographer from the Greek city of Halicarnassus, part of the Persian Empire (now Bodrum, Turkey) and a later citizen of Thurii in modern Calabria ( Italy). He is known for ha ...
in about 420 BCE, though his example (birds serving crocodiles) appears to occur only rarely. The role of cleaning symbioses has been debated by biologists for over thirty years. Some believe that cleaning represents selfless co-operation, essentially pure mutualism, increasing the fitness of both individuals. Others such as
Robert Trivers Robert Ludlow "Bob" Trivers (; born February 19, 1943) is an American evolutionary biologist and sociobiologist. Trivers proposed the theories of reciprocal altruism (1971), parental investment (1972), facultative sex ratio determination (1973), ...
hold that it illustrates mutual selfishness,
reciprocal altruism In evolutionary biology, reciprocal altruism is a behaviour whereby an organism acts in a manner that temporarily reduces its fitness while increasing another organism's fitness, with the expectation that the other organism will act in a similar m ...
. Others again believe that cleaning behaviour is simply one-sided exploitation, a form of
parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
. Cheating, where either a cleaner sometimes harms its client, or a predatory species mimics a cleaner, also occurs. Predatory cheating is analogous to Batesian mimicry, as where a harmless hoverfly mimics a stinging wasp, though with the tables turned. Some genuine cleaner fish, such as gobies and wrasse, have the same colours and patterns, in an example of convergent evolution. Mutual resemblance among cleaner fish is analogous to
Müllerian mimicry 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 ...
, as where stinging bees and wasps mimic each other.


History

In his '' Histories'' (book II), the ancient Greek historian
Herodotus Herodotus ( ; grc, , }; BC) was an ancient Greek historian and geographer from the Greek city of Halicarnassus, part of the Persian Empire (now Bodrum, Turkey) and a later citizen of Thurii in modern Calabria ( Italy). He is known for ha ...
wrote: Herodotus thus claimed (circa 440 BCE) that Nile crocodiles had what would now be called a cleaning symbiosis with the bird he called the ''trochilus'', possibly a
sandpiper Sandpipers are a large family, Scolopacidae, of waders. They include many species called sandpipers, as well as those called by names such as curlew and snipe. The majority of these species eat small invertebrates picked out of the mud or soil. ...
. In 1906
Henry Scherren Henry James Wilson Scherren (10 February 1843 – 25 April 1911), usually known as Henry Scherren or in encyclopaedia articles as H. Sc. was the author of various books on natural history for adults and children, with notable illustrations inclu ...
quoted John Mason Cook, son of travel agent
Thomas Cook Thomas Cook (22 November 1808 – 18 July 1892) was an English businessman. He is best known for founding the travel agency Thomas Cook & Son. He was also one of the initial developers of the "package tour" including travel, accommodation ...
, as reporting from Egypt that he had seen some
spur-winged plover The spur-winged lapwing or spur-winged plover (''Vanellus spinosus'') is a lapwing species, one of a group of largish waders in the family Charadriidae. It is one of several species of wader supposed to be the "trochilus" bird said by Herodotu ...
s approach a crocodile, which opened its jaws for them: MacFarland and Reeder, reviewing the evidence, found that


A disputed relationship

Cleaning symbiosis is a relationship between a pair of animals of different species, involving the removal and subsequent ingestion of ectoparasites, diseased and injured tissue, and unwanted food items from the surface of the host organism (the client) by the cleaning organism (the cleaner). Its status has been debated by biologists, with viewpoints ranging from pure mutualism through to a form of exploitative
parasitism Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
by the cleaner.
Marine biologist Marine biology is the scientific study of the biology of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifie ...
Alexandra Grutter explains:


Selfless co-operation

Grutter and her colleague Robert Poulin, reviewing over thirty years of debate by biologists on cleaning symbioses, argue that "Cleaning symbioses may not be mutualistic associations but rather one-sided exploitation. However, one must then ask why no counter-adaptation has evolved in clients to free them from this exploitation. If clients are the puppets of cleaners, then the fitness consequences of being exploited must be small". They quote as an example of an early position, C. Limbaugh writing in 1961: "From the standpoint of the philosopher of biology, the extent of cleaning behavior in the ocean emphasizes the role of co-operation in nature as opposed to the tooth-and-claw struggle for existence".


Mutual selfishness

In 1971, mathematical biologist
Robert Trivers Robert Ludlow "Bob" Trivers (; born February 19, 1943) is an American evolutionary biologist and sociobiologist. Trivers proposed the theories of reciprocal altruism (1971), parental investment (1972), facultative sex ratio determination (1973), ...
wrote more carefully "Cleaner organisms and their hosts meet the preconditions for the evolution of reciprocally altruistic behavior. The host's altruism is to be explained as benefiting him because of the advantage of being able quickly and repeatedly to return to the same cleaner" (i.e. mutual selfishness).


One-sided exploitation

By 1987 G. S. Losey wrote less optimistically "Cleaners are nothing but very clever behavioral parasites ... that have taken advantage of the rewarding aspects of tactile stimulation, found in nearly all vertebrates." Poulin and Grutter remark that "Over the last few decades, ... the opinion of scientists regarding cleaning symbioses has changed, from selfless cooperation, to a mutually beneficial interaction, and finally to a one-sided exploitation."


Biological range

Cleaning symbiosis is known from several groups of animals both in the sea and on land (see table). Cleaners include fish, shrimps and birds; clients include a much wider range of fish, marine reptiles including turtles and iguanas, octopus, whales, and terrestrial mammals. Cleaning symbioses with reptile clients include fish cleaning the teeth of
American crocodile The American crocodile (''Crocodylus acutus'') is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas, with populations present from South Florida and the coas ...
s (''Crocodylus acutus''), geckos eating mosquitoes on
Aldabra giant tortoise The Aldabra giant tortoise (''Aldabrachelys gigantea'') is a species of tortoise in the family Testudinidae. The species is endemic to the islands of the Aldabra Atoll in the Seychelles. It is one of the largest tortoises in the world.Pritcha ...
s (''Geochelone gigantea'') and scarlet crabs (''
Grapsus grapsus ''Grapsus grapsus'' is one of the most common crabs along the western coast of the Americas. It is known as the red rock crab, or, along with crabs such as '' Percnon gibbesi'', as the Sally Lightfoot crab. Distribution ''Grapsus grapsus'' is fo ...
''), and three species of Galapagos finches removing ticks from
marine iguana The marine iguana (''Amblyrhynchus cristatus''), also known as the sea iguana, saltwater iguana, or Galápagos marine iguana, is a species of iguana found only on the Galápagos Islands (Ecuador). Unique among modern lizards, it is a marine rept ...
s (''Amblyrhynchus cristatus''). The best known cleaning symbioses are among marine fishes, where several species of small fish, notably of wrasse, are specialised in colour, pattern and behaviour as cleaners, providing a cleaning and
ectoparasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
removal service to larger, often predatory fish. Cleaner species, as shown in the table, vary widely in their degree of dependence on their clients. Some are essentially pure obligate symbionts like the cleaner wrasse; some are opportunistic or facultative symbionts, like the orange chromide or some cleaner shrimps; and some, like the oxpeckers, combine a little eating of parasites (beneficial to client) with taking of blood (harmful to client), their favoured food.


Mimicry among cleaner fish


Mutual mimicry among cleaner fish

Many
cleaner fish Cleaner fish are fish that show a specialist feeding strategy by providing a service to other species, referred to as clients, by removing dead skin, ectoparasites, and infected tissue from the surface or gill chambers. This example of cleaning ...
in different families, such as the Caribbean neon goby (''
Elacatinus evelynae ''Elacatinus evelynae'', the sharknose goby, Caribbean cleaner goby, Caribbean cleaning goby, is a species of goby native to the Western Atlantic Ocean from the Bahamas and the Lesser Antilles to the northern coast of South America, as well as t ...
'') and the
Indo-Pacific The Indo-Pacific is a vast biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the ...
cleaner wrasse ('' Labroides dimidiatus'') share the distinctive combination of a long narrow body, a longitudinal stripe, a blue colour, and small size. " Convergent signalling among cleaners, using size, stripes and colour, should facilitate their recognition by fish clients." This is analogous to
Müllerian mimicry 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 ...
where genuinely
aposematic Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or ...
species (such as wasps) mimic each other's warning colours.


Aggressive mimicry of cleaner fish by blennies

The sabre-toothed blenny (''Aspidontus taeniatus'') is a predatory blenny, an aggressive mimic which accurately resembles the bluestreak cleaner wrasse, not only in colour and pattern, but also in the ritualised dance the cleaner wrasse makes when potential client fish swim nearby. However, instead of providing the cleaning service that it signals, it bites off pieces of healthy skin, scales and mucus from the host and then swims rapidly away to safety. The effect of aggressive
mimicry 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 f ...
in a cleaning symbiosis is analogous to Batesian mimicry, where a harmless "edible mimetic species copies the warning signal of a noxious, aposematic model species, thereby gaining protection from predators". As in Batesian mimicry, the rate of successful attacks on cleaning clients by the bluestriped fangblenny ('' Plagiotremus rhinorhynchos''), which like the sabre-toothed blenny mimic the bluestreak cleaner wrasse ('' Labroides dimidiatus''), is frequency-dependent, meaning that the mimicry is more effective when the
cheating Cheating generally describes various actions designed to subvert rules in order to obtain unfair advantages. This includes acts of bribery, cronyism and nepotism in any situation where individuals are given preference using inappropriate crit ...
fangblenny is rare compared to the cleaner wrasse. The difference, however, is that the aggressive mimic is inserting itself into a co-operative relationship (between cleaner and client), whereas "Batesian mimics insert themselves into an antagonistic predator–prey interaction (where the models are the unpalatable prey)." The fangblenny has evolved an
opioid Opioids are substances that act on opioid receptors to produce morphine-like effects. Medically they are primarily used for pain relief, including anesthesia. Other medical uses include suppression of diarrhea, replacement therapy for opioid use ...
-containing venom which dulls pain and lowers blood pressure, confusing the bitten host and giving the cheating mimic time to escape.


References


External links


Coral Reef Ecology Laboratory
(publications by Grutter et al.) {{Biological interaction-footer Evolutionary biology Ethology Mutualism (biology) Articles containing video clips