Editing Commensalism (section)

== Examples of commensal relationships ==
[[File:Rock dove - natures pics.jpg|thumb|[[Domestic pigeon|Domestic]] and [[feral pigeons]] (''Columba livia domestica'') are commensals, having lived alongside humans for thousands of years after being domesticated from the [[rock dove]] (''Columba livia''). Due to its range being expanded with human assistance, the pigeon has a [[cosmopolitan distribution]].<ref>{{Cite journal |last1=Tang |first1=Qian |last2=Low |first2=Gabriel Weijie |last3=Lim |first3=Jia Ying |last4=Gwee |first4=Chyi Yin |last5=Rheindt |first5=Frank E. |date=2018-07-21 |title=Human activities and landscape features interact to closely define the distribution and dispersal of an urban commensal |journal=Evolutionary Applications |volume=11 |issue=9 |pages=1598–1608 |doi=10.1111/eva.12650 |issn=1752-4571 |pmc=6183452 |pmid=30344630|bibcode=2018EvApp..11.1598T }}</ref> ]]
The commensal pathway was traversed by animals that fed on refuse around human habitats or by animals that preyed on other animals drawn to human camps. Those animals established a commensal relationship with humans in which the animals benefited but the humans received little benefit or harm. Those animals that were most capable of taking advantage of the resources associated with human camps would have been the 'tamer' individuals: less aggressive, with shorter [[Fight-or-flight response|fight-or-flight]] distances. Later, these animals developed closer social or economic bonds with humans and led to a domestic relationship.<ref name=zeder2012/><ref name=larson2014/>

The leap from a [[synanthrope|synanthropic]] population to a domestic one could only have taken place after the animals had progressed from anthropophily to habituation to commensalism and partnership, at which point the establishment of a reciprocal relationship between animal and human would have laid the foundation for domestication, including captivity and then human-controlled breeding. From this perspective, animal domestication is a [[coevolution]]ary process in which a population responds to selective pressure while adapting to a novel [[Ecological niche|niche]] that includes another species with evolving behaviors.<ref name=larson2014/>

===Dogs and humans===
The [[dog]] was the first domesticated animal and was domesticated and widely established across [[Eurasia]] before the end of the [[Pleistocene]], well before the cultivation of crops or the [[domestication]] of other animals.<ref name=larson2012/> The dog is often hypothesised to be a classic example of a domestic animal that likely traveled a commensal pathway into domestication. Archaeological evidence, such as the [[Bonn–Oberkassel dog]] dating to ~14,000 BP,<ref name=janssens2018/> supports the hypothesis that dog domestication preceded the emergence of agriculture <ref name=vila1997/><ref name=thalmann2013/> and began close to the [[Last Glacial Maximum]] when hunter-gatherers preyed on [[megafauna]].

The wolves more likely drawn to human camps were the less aggressive, subdominant pack members with lowered flight response, higher stress thresholds, and less wary around humans, and therefore better candidates for domestication.<ref name=zeder2012/>
Proto-dogs might have taken advantage of carcasses left on site by early hunters, assisted in capturing prey, or provided defense from large competing predators at kills.<ref name=thalmann2013/> However, the extent to which proto-domestic wolves could have become dependent on this way of life prior to domestication and without human provisioning is unclear and highly debated. In contrast, [[cats]] may have become fully dependent on a commensal lifestyle before being domesticated by preying on other commensal animals, such as rats and mice, without any human provisioning. The debate over the extent to which some wolves were commensal with humans before domestication stems from the debate over the level of human intentionality in domestication, which remains untested.<ref name=larson2014/><ref name=hulmebeaman2016/>

The earliest sign of domestication in dogs was the [[Neoteny|neotenization]] (retaining juvenile features into adulthood) of skull morphology<ref name=morey1992/><ref name=trut1999/><ref name=zeder2012/> and the shortening of snout length that results in tooth crowding, reduction in tooth size, and a reduction in the number of teeth,<ref name=turnbull1974/><ref name=zeder2012/> which has been attributed to the strong selection for reduced aggression.<ref name=trut1999/><ref name=zeder2012/> This process may have begun during the initial commensal stage of dog domestication, even before humans began to be active partners in the process.<ref name=zeder2012/><ref name=larson2014/>

A [[Mitochondrion|mitochondrial]], microsatellite, and [[Y chromosome|Y-chromosome]] assessment of two wolf populations in North America combined with satellite [[telemetry]] data revealed significant genetic and morphological differences between one population that migrated with and preyed upon caribou and another territorial ecotype population that remained in a [[Taiga|boreal coniferous forest]]. Although these two populations spend a period of the year in the same place, and though there was evidence of gene flow between them, the difference in prey-habitat specialization has been sufficient to maintain genetic and even coloration divergence.<ref name=musiani2007/><ref name=larson2014/>

A different study has identified the remains of a population of extinct [[Pleistocene]] [[Beringian wolf|Beringian wolves]] with unique mitochondrial signatures. The skull shape, tooth wear, and [[isotopic signature]]s suggested these remains were derived from a population of specialist [[megafauna]] hunters and scavengers that became extinct while less specialized wolf [[ecotype]]s survived.<ref name=leonard2007/><ref name=larson2014/> Analogous to the modern wolf ecotype that has evolved to track and prey upon caribou, a Pleistocene wolf population could have begun following mobile [[hunter-gatherer]]s, thus slowly acquiring genetic and [[Phenotype|phenotypic]] differences that would have allowed them to adapt to the [[human habitat]] more successfully.<ref name=wolpert2013/><ref name=larson2014/>

===''Aspergillus'' and ''Staphylococcus''===
{{See also|Aspergillus|Staphylococcus}}
Numerous genera of [[bacteria]] and [[fungi]] live on and in the human body as part of its natural flora. The fungal genus ''[[Aspergillus]]'' is capable of living under considerable environmental stress, and thus is capable of colonising the upper gastrointestinal tract where relatively few examples of the body's gut flora can survive due to highly acidic or alkaline conditions produced by gastric acid and digestive juices. While ''Aspergillus'' normally produces no symptoms, in individuals who are immunocompromised or suffering from existing conditions such as [[tuberculosis]], a condition called [[aspergillosis]] can occur, in which populations of ''Aspergillus'' grow out of control.{{cn|date=June 2024}}

''[[Staphylococcus aureus]]'', a common bacterial species, is known best for its numerous pathogenic strains that can cause numerous illnesses and conditions. However, many strains of ''S. aureus'' are metabiotic commensals, and are present on roughly 20 to 30% of the human population as part of the [[skin flora]].<ref name=pmid9227864/> ''S. aureus'' also benefits from the variable ambient conditions created by the body's mucous membranes, and as such can be found in the [[oral cavity|oral]] and [[nasal cavity|nasal cavities]], as well as inside the [[ear canal]]. Other ''Staphylococcus'' species including ''[[Staphylococcus warneri|S. warneri]]'', ''[[Staphylococcus lugdunensis|S. lugdunensis]]'' and ''[[Staphylococcus epidermidis|S. epidermidis]]'', will also engage in commensalism for similar purposes.{{cn|date=June 2024}}

=== ''Nitrosomonas'' spp and ''Nitrobacter'' spp ===
Commensalistic relationships between microorganisms include situations in which the waste product of one microorganism is a substrate for another species. One good example is nitrification — the oxidation of [[ammonium|ammonium ion]] to [[nitrate]]. Nitrification occurs in two steps: first, bacteria such as ''[[Nitrosomonas]]'' [[Species#Abbreviations|spp.]] and certain [[crenarchaeota|crenarchaeote]]s oxidize ammonium to [[nitrite]]; and second, nitrite is oxidized to nitrate by ''[[Nitrobacter]]'' spp. and similar bacteria. ''Nitrobacter'' spp. benefit from their association with ''Nitrosomonas'' spp. because they use nitrite to obtain energy for growth.{{cn|date=June 2024}}

Commensalistic associations also occur when one microbial group modifies the environment to make it better suited for another organism. The synthesis of acidic waste products during [[fermentation]] stimulates the proliferation of more acid-tolerant microorganisms, which may be only a minor part of the microbial community at neutral pH. A good example is the succession of microorganisms during milk spoilage.{{cn|date=June 2024}}

[[Biofilm]] formation provides another example. The colonization of a newly exposed surface by one type of microorganism (an initial colonizer) makes it possible for other microorganisms to attach to the microbially modified surface.{{cn|date=June 2024}}

=== Octocorals and brittle stars ===

In deep-sea, benthic environments there is an associative relationship between [[Octocorallia|octocorals]] and [[brittle star]]s. Due to the currents flowing upward along seamount ridges, atop these ridges there are colonies of suspension feeding corals and sponges, and brittle stars that grip tight to them and get up off the sea floor. A specific documented commensal relationship is between the ophiuran ''Ophiocreas oedipus'' Lyman and the octocoral primnoid ''Metallogorgia melanotrichos''.{{cn|date=June 2024}}

Historically, commensalism has been recognized as the usual type of association between brittle stars and octocorals.<ref>{{cite journal | url=https://pubmed.ncbi.nlm.nih.gov/21962750/ | pmid=21962750 | doi=10.1016/B978-0-12-385529-9.00002-0 | title=Biology of deep-water octocorals | journal=Advances in Marine Biology | year=2011 | volume=60 | pages=41–122 | last1=Watling | first1=Les | last2=France | first2=Scott C. | last3=Pante | first3=Eric | last4=Simpson | first4=Anne | isbn=9780123855299 }}</ref> In this association, the ophiurans benefit directly by being elevated through facilitating their feeding by suspension, while the octocorals do not seem to benefit or be harmed by this relationship.<ref>{{cite journal | jstor=24844596 | title=Size structure of dense populations of the brittle star Ophiura sarsii (Ophiuroidea: Echinodermata) in the bathyal zone around Japan | last1=Fujita | first1=Toshihiko | last2=Ohta | first2=Suguru | journal=Marine Ecology Progress Series | year=1990 | volume=64 | issue=1/2 | pages=113–122 | doi=10.3354/meps064113 | bibcode=1990MEPS...64..113F | doi-access=free }}</ref>

Recent studies in the Gulf of Mexico have suggested that there are actually some benefits to the octocorals, such as receiving a cleaning action by the brittle star as it slowly moves around the coral.<ref>{{cite journal |doi=10.3354/meps11697 |url=https://www.int-res.com/articles/meps_oa/m549p089.pdf |access-date=24 May 2023 |title=Mutualistic symbiosis with ophiuroids limited the impact of the Deepwater Horizon oil spill on deep-sea octocorals |year=2016 |last1=Girard |first1=F. |last2=Fu |first2=B. |last3=Fisher |first3=CR |journal=Marine Ecology Progress Series |volume=549 |pages=89–98 |bibcode=2016MEPS..549...89G }}</ref> In some cases, a close relationship occurs between cohabiting species, with the interaction beginning from their juvenile stages.<ref>{{cite journal |last1=Mejía-Quintero |first1=Katherine |last2=Borrero-Pérez |first2=Giomar H. |last3=Montoya-Cadavid |first3=Erika |title=Callogorgia spp. and Their Brittle Stars: Recording Unknown Relationships in the Pacific Ocean and the Caribbean Sea |journal=Frontiers in Marine Science |date=2021 |volume=8 |doi=10.3389/fmars.2021.735039 |issn=2296-7745|doi-access=free |bibcode=2021FrMaS...835039M }} [[File:CC-BY icon.svg|50px]]  Text was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/  Creative Commons Attribution 4.0 International License].</ref>