Editing Coevolution (section)

==Hosts and parasites==
{{Main|Host–parasite coevolution}}

===Parasites and sexually reproducing hosts===
[[Host–parasite coevolution]] is the coevolution of a [[host (biology)|host]] and a [[parasite]].<ref name="Woolhouse">{{cite journal |doi=10.1038/ng1202-569 |last1=Woolhouse |first1=M. E. J. |last2=Webster |first2=J. P. |last3=Domingo |first3=E. |last4=Charlesworth |first4=B. |last5=Levin |first5=B. R. |title=Biological and biomedical implications of the coevolution of pathogens and their hosts |journal=[[Nature Genetics]] |date=December 2002 |pmid=12457190 |volume=32 |issue=4 |pages=569–77 |url=http://www.era.lib.ed.ac.uk/bitstream/1842/689/2/Charlesworth_Woolhouse.pdf |hdl=1842/689 |s2cid=33145462 |hdl-access=free }}</ref> A general characteristic of many viruses, as [[obligate parasite]]s, is that they coevolved alongside their respective hosts. Correlated mutations between the two species enter them into an evolution arms race. Whichever organism, host or parasite, that cannot keep up with the other will be eliminated from their habitat, as the species with the higher average population fitness survives. This race is known as the [[Red Queen hypothesis]].<ref>{{cite journal |last=Van Valen |first=L. |date=1973 |title=A New Evolutionary Law |journal=Evolutionary Theory |volume=1 |pages=1–30}} cited in: [http://pespmc1.vub.ac.be/REDQUEEN.html The Red Queen Principle]</ref> The Red Queen hypothesis predicts that sexual reproduction allows a host to stay just ahead of its parasite, similar to the [[Red Queen's race]] in ''[[Through the Looking-Glass]]'': "it takes all the running ''you'' can do, to keep in the same place".<ref>{{cite book |last=Carroll |first=Lewis |author-link=Lewis Carroll |orig-year=1871 |title=Through the Looking-glass: And what Alice Found There |url=https://books.google.com/books?id=cJJZAAAAYAAJ |publisher=Macmillan |date=1875 |page=42 |quote=it takes all the running ''you'' can do, to keep in the same place.}}</ref> The host reproduces sexually, producing some offspring with immunity over its parasite, which then evolves in response.<ref>{{cite journal |doi=10.1038/srep10004 |last=Rabajante |first=J. |display-authors=etal |title=Red Queen dynamics in multi-host and multi-parasite interaction system |journal=[[Scientific Reports]] |year=2015 |volume=5 |pages=10004 |pmid=25899168 |pmc=4405699 |bibcode=2015NatSR...510004R}}</ref>

The parasite–host relationship probably drove the prevalence of sexual reproduction over the more efficient asexual reproduction. It seems that when a parasite infects a host, sexual reproduction affords a better chance of developing resistance (through variation in the next generation), giving sexual reproduction variability for fitness not seen in the asexual reproduction, which produces another generation of the organism susceptible to infection by the same parasite.<ref>{{cite web |title=Sexual reproduction works thanks to ever-evolving host, parasite relationships |website=PhysOrg |url=https://phys.org/news/2011-07-sexual-reproduction-ever-evolving-host-parasite.html |date=7 July 2011}}</ref><ref>{{cite journal |last1=Morran |first1=L.T. |author2=Schmidt, O.G. |author3=Gelarden, I.A. |author4=Parrish, R.C. II |author5= Lively, C.M. |title=Running with the Red Queen: Host-Parasite Coevolution Selects for Biparental Sex |journal=Science |volume=333 |issue=6039 |pages=216–8 |date=8 July 2011 |id=Science.1206360 |bibcode=2011Sci...333..216M |doi=10.1126/science.1206360 |pmid=21737739 |pmc=3402160}}</ref><ref>{{cite encyclopedia |author=Hogan, C. Michael |date=2010 |url=https://editors.eol.org/eoearth/wiki/Virus |title=Virus |encyclopedia=Encyclopedia of Earth |editor=Cutler Cleveland |editor2=Sidney Draggan}}</ref> Coevolution between host and parasite may accordingly be responsible for much of the genetic diversity seen in normal populations, including blood-plasma polymorphism, protein polymorphism, and histocompatibility systems.<ref>{{cite journal |author1=Anderson, R. |author2=May, R. |date=October 1982 |title=Coevolution of hosts and parasites |journal=Parasitology |volume=85 |issue=2 |pages=411–426 |doi=10.1017/S0031182000055360 |pmid=6755367|s2cid=26794986 }}</ref>

[[File:Reed warbler cuckoo.jpg|upright|thumb|[[Brood parasite]]: [[Eurasian reed warbler]] raising a [[common cuckoo]]<ref name=Weiblen/>]]

===Brood parasites===
{{Main|Brood parasitism}}

[[Brood parasite|Brood parasitism]] demonstrates close coevolution of host and parasite, for example in some [[cuckoo]]s. These birds do not make their own nests, but lay their eggs in nests of other species, ejecting or killing the eggs and young of the host and thus having a strong negative impact on the host's reproductive fitness. Their eggs are camouflaged as eggs of their hosts, implying that hosts can distinguish their own eggs from those of intruders and are in an evolutionary arms race with the cuckoo between camouflage and recognition. Cuckoos are counter-adapted to host defences with features such as thickened eggshells, shorter incubation (so their young hatch first), and flat backs adapted to lift eggs out of the nest.<ref name=Weiblen>{{cite web |last1=Weiblen |first1=George D. |title=Interspecific Coevolution |url=http://geo.cbs.umn.edu/Weiblen2003.pdf |publisher=Macmillan |date=May 2003}}</ref><ref>{{cite journal |last1=Rothstein |first1=S.I |year=1990 |title=A model system for coevolution: avian brood parasitism |journal=Annual Review of Ecology and Systematics |volume=21 |pages=481–508 |doi=10.1146/annurev.ecolsys.21.1.481}}</ref><ref>{{Cite book |last=Davies |first=Nicholas B. |others=McCallum, James (Wildlife artist) |title=Cuckoo : cheating by nature |date=7 April 2015 |isbn=978-1-62040-952-7 |edition=First U.S. |location=New York, NY |oclc=881092849}}</ref>

===Antagonistic coevolution===

Antagonistic coevolution is seen in the [[harvester ant]] species ''[[Pogonomyrmex barbatus]]'' and ''[[Pogonomyrmex rugosus]]'', in a relationship both parasitic and mutualistic. The queens are unable to produce worker ants by mating with their own species. Only by crossbreeding can they produce workers. The winged females act as parasites for the males of the other species as their sperm will only produce sterile hybrids. But because the colonies are fully dependent on these hybrids to survive, it is also mutualistic. While there is no genetic exchange between the species, they are unable to evolve in a direction where they become too genetically different as this would make crossbreeding impossible.<ref name="Herrmann Cahan pp. 20141771–20141771">{{cite journal |last1=Herrmann |first1=M. |last2=Cahan |first2=S. H. |title=Inter-genomic sexual conflict drives antagonistic coevolution in harvester ants |journal=Proceedings of the Royal Society B: Biological Sciences |volume=281 |issue=1797 |date=29 October 2014 |doi=10.1098/rspb.2014.1771 |pmid=25355474 |pages=20141771 |pmc=4240986}}</ref>