Editing Reciprocal altruism (section)

===Cleaner fish===
{{further|Cleaning symbiosis}}
[[File:Cleaner station komodo.jpg|thumb|250px|[[Cleaning symbiosis]]: a small cleaner [[wrasse]] (''Labroides dimidiatus'') with [[Animal coloration|advertising coloration]] services a big eye squirrelfish (''[[Priacanthidae|Priacanthus hamrur]]'') in an apparent example of reciprocal altruism.]]

An example of reciprocal altruism is [[cleaning symbiosis]], such as between [[cleaner fish]] and their hosts, though cleaners include shrimps and birds, and clients include fish, turtles, octopuses and mammals.<ref name=Grutter>{{cite journal | title=Cleaning symbioses from the parasites' perspective | author=Grutter, Alexandra S. | journal=Parasitology | year=2002 | volume=124 | issue=7 | pages=S65–S81 | doi=10.1017/S0031182002001488| pmid=12396217 | s2cid=26816332 }}</ref>   Aside from the apparent [[symbiosis]] of the cleaner and the host during actual cleaning, which cannot be interpreted as altruism, the host displays additional behaviour that meets the criteria for delayed return altruism:

The host fish allows the cleaner fish free entrance and exit and does not eat the cleaner, even after the cleaning is done.<ref name="Eibel-Eibesfeldt">{{cite journal | doi = 10.1111/j.1439-0310.1955.tb01523.x | title = Über Symbiosen, Parasitismus und andere besondere zwischenartliche Beziehungen tropischer Meeresfische1 | year = 2010 | last1 = Eibi-Eibesfeldt | first1 = T | journal = Zeitschrift für Tierpsychologie | volume = 12 | issue = 2 | pages = 203–219 }}</ref><ref name="Heidiger">{{cite journal |first=H. |last=Heidiger |title=Putzer-fische im aquarium |journal=Natur und Museum |volume=98 |pages=89–96 |year=1968 }}</ref><ref name="Randall1">{{cite journal | last1 = Randall | first1 = J. E. | year = 1958 | title = A review of the Labrid fish genus Labriodes with descriptions of two new species and notes on ecology | journal = Pacific Science | volume = 12 | issue =4 | pages = 327–347 |url=https://scholarspace.manoa.hawaii.edu/bitstream/10125/7923/vol12n4-327-347.pdf |archive-url=https://web.archive.org/web/20200806161617/https://scholarspace.manoa.hawaii.edu/bitstream/10125/7923/vol12n4-327-347.pdf |archive-date=2020-08-06 |url-status=live}}</ref><ref name="Randall2">{{cite journal | last1 = Randall | first1 = J. E. | year = 1962 | title = Fish service stations | journal = Sea Frontiers | volume = 8 | pages = 40–47 }}</ref> The host signals the cleaner it is about to depart the cleaner's locality, even when the cleaner is not in its body. The host sometimes chases off possible dangers to the cleaner.<ref name="Randall2" />

The following evidence supports the hypothesis:

The cleaning by cleaners is essential for the host. In the absence of cleaners the hosts leave the locality or suffer from injuries inflicted by [[ectoparasites]].<ref name="Feder">{{cite book |first=H.M. |last=Feder |chapter=Cleaning symbioses in the marine environment |editor-first=S.M. |editor-last=Henry |title=Symbiosis |publisher=Academic Press |year=1966 |pages=327–380 |oclc=841865823 |volume=1}}</ref> There is difficulty and danger in finding a cleaner. Hosts leave their element to get cleaned.<ref name="Randall2" /> Others wait no longer than 30 seconds before searching for cleaners elsewhere.<ref name="Eibel-Eibesfeldt" />

A key requirement for the establishment of reciprocal altruism is that the same two individuals must interact repeatedly, as otherwise the best strategy for the host would be to eat the cleaner as soon as cleaning was complete. This constraint imposes both a spatial and a temporal condition on the cleaner and on its host. Both individuals must remain in the same physical location, and both must have a long enough lifespan, to enable multiple interactions. There is reliable evidence that individual cleaners and hosts do indeed interact repeatedly.<ref name="Randall1" /><ref name="Feder" /><ref name="Limbaugh">{{cite journal | last1 = Limbaugh | first1 = C. | last2 = Pederson | first2 = H. | last3 = Chase | first3 = F. | year = 1961 | title = Shrimps that clean fishes | url =http://www.ingentaconnect.com/content/umrsmas/bullmar/1961/00000011/00000001/art00011 | journal = Bull. Mar. Sci. Gulf Caribb. | volume = 11 | issue =1 | pages = 237–257 }}</ref>

This example meets some, but not all, of the criteria described in Trivers's model. In the cleaner-host system the benefit to the cleaner is always immediate. However, the evolution of reciprocal altruism is contingent on opportunities for future rewards through repeated interactions. In one study, nearby host fish observed "cheater" cleaners and subsequently avoided them.<ref name="bshary">{{cite journal | last1 = Bshary | first1 = R. | year = 2002 | title = Biting cleaner fish use altruism to deceive image-scoring client reef fish | journal = Proceedings of the Royal Society B | volume = 269 | issue = 1505 | pages = 2087–93 | doi=10.1098/rspb.2002.2084| pmid = 12396482 | pmc = 1691138 }}</ref> In these examples, true reciprocity is difficult to demonstrate since failure means the death of the cleaner. However, if Randall's claim that hosts sometimes chase off possible dangers to the cleaner is correct, an experiment might be constructed in which reciprocity could be demonstrated.<ref name="Randall1" />  In actuality this is one of Trivers' examples of Delayed Return Altruism as discussed by Rothstein and Pierotti 1988.