Editing Parasitism (section)

==== Cospeciation ====

A parasite sometimes undergoes [[cospeciation]] with its host, resulting in the pattern described in [[Fahrenholz's rule]], that the phylogenies of the host and parasite come to mirror each other.<ref name=Page>{{cite book |last=Page |first=Roderic D. M. |publisher=John Wiley |date=27 January 2006 |isbn=978-0-470-01617-6 |doi=10.1038/npg.els.0004124|title=Encyclopedia of Life Sciences |chapter=Cospeciation }}</ref>

An example is between the [[simian foamy virus]] (SFV) and its primate hosts. The phylogenies of SFV polymerase and the mitochondrial [[cytochrome c oxidase subunit II]] from African and Asian primates were found to be closely congruent in branching order and divergence times, implying that the simian foamy viruses cospeciated with Old World primates for at least 30&nbsp;million years.<ref name="SwitzerSalemi2005">{{cite journal |last1=Switzer |first1=William M. |last2=Salemi |first2=Marco |last3=Shanmugam |first3=Vedapuri |last4=Gao |first4=Feng |last5=Cong |first5=Mian-er |last6=Kuiken |first6=Carla |last7=Bhullar |first7=Vinod |last8=Beer |first8=Brigitte E. |last9=Vallet |first9=Dominique |last10=Gautier-Hion |first10=Annie |last11=Tooze |first11=Zena |last12=Villinger |first12=Francois |last13=Holmes |first13=Edward C. |last14=Heneine |first14=Walid |display-authors=3 |title=Ancient co-speciation of simian foamy viruses and primates |journal=Nature |volume=434 |issue=7031 |year=2005 |pages=376–380 |doi=10.1038/nature03341|pmid=15772660 |bibcode=2005Natur.434..376S |s2cid=4326578 |url=https://zenodo.org/record/1233279 }}</ref>

The presumption of a shared evolutionary history between parasites and hosts can help elucidate how host taxa are related. For instance, there has been a dispute about whether [[Phoenicopteriformes|flamingos]] are more closely related to [[Ciconiiformes|storks]] or [[Anseriformes|ducks]]. The fact that flamingos share parasites with ducks and geese was initially taken as evidence that these groups were more closely related to each other than either is to storks. However, evolutionary events such as the duplication, or the extinction of parasite species (without similar events on the host phylogeny) often erode similarities between host and parasite phylogenies. In the case of flamingos, they have similar lice to those of [[grebe]]s. Flamingos and grebes do have a common ancestor, implying cospeciation of birds and lice in these groups. Flamingo lice then [[host switch|switched hosts]] to ducks, creating the situation which had confused biologists.<ref name=JohnsonKennedy2006>{{cite journal|last1=Johnson|first1=K. P.|last2=Kennedy|first2=M.|last3=McCracken|first3=K. G|title=Reinterpreting the origins of flamingo lice: cospeciation or host-switching?|journal=Biology Letters|volume=2|issue=2|year=2006|pages=275–278|doi=10.1098/rsbl.2005.0427|pmc=1618896|pmid=17148381}}</ref>

[[File:Toxoplasma gondii (2).jpg|thumb|The protozoan ''[[Toxoplasma gondii]]'' facilitates its transmission by [[Behavior-altering parasites|inducing behavioral changes]] in rats through infection of neurons in their [[central nervous system]].]]

Parasites infect [[sympatry|sympatric]] hosts (those within their same geographical area) more effectively, as has been shown with [[Digenea|digenetic trematodes]] infecting lake snails.<ref name="Lively00"/> This is in line with the [[Red Queen hypothesis]], which states that interactions between species lead to constant natural selection for coadaptation. Parasites track the locally common hosts' phenotypes, so the parasites are less infective to [[allopatric speciation|allopatric]] hosts, those from different geographical regions.<ref name="Lively00">{{cite journal |last1=Lively |first1=C. M. |last2=Dybdahl |first2=M. F. |url=https://public.wsu.edu/~dybdahl/nature00.pdf |archive-url=https://web.archive.org/web/20160607131917/http://public.wsu.edu/~dybdahl/nature00.pdf |archive-date=7 June 2016 |url-status=live |title=Parasite adaptation to locally common host genotypes |journal=Nature |volume=405 |issue=6787 |pages=679–81 |year=2000 |pmid=10864323 |doi=10.1038/35015069 |bibcode=2000Natur.405..679L |s2cid=4387547 }}</ref>