Editing Frequency-dependent selection

{{Short description|Evolutionary process}}
'''Frequency-dependent selection''' is an evolutionary process by which the [[fitness (biology)|fitness]] of a [[phenotype]] or [[genotype]] depends on the phenotype or genotype composition of a given [[population]].
* In '''positive''' frequency-dependent selection, the fitness of a phenotype or [[genotype]] increases as it becomes more common.
* In '''negative''' frequency-dependent selection, the fitness of a phenotype or [[genotype]] decreases as it becomes more common. This is an example of [[balancing selection]].
* More generally, frequency-dependent selection includes when biological interactions make an individual's fitness depend on the frequencies of other phenotypes or genotypes in the population.<ref>{{cite journal |last1=Lewontin |first1=Richard |title=A general method for investigating the equilibrium of gene frequency in a population |journal=Genetics |year=1958 |volume=43 |issue=3 |pages=419–434|doi=10.1093/genetics/43.3.419 |pmid=17247767 |pmc=1209891 }}</ref>

Frequency-dependent selection is usually the result of interactions between species (predation, parasitism, or competition), or between genotypes within species (usually competitive or symbiotic), and has been especially frequently discussed with relation to [[anti-predator adaptations]]. Frequency-dependent selection can lead to [[Polymorphism (biology)|polymorphic]] equilibria, which result from interactions among genotypes within species, in the same way that multi-species equilibria require interactions between species in competition (e.g. where ''α''<sub>ij</sub> parameters in [[Lotka-Volterra]] competition equations are non-zero).  Frequency-dependent selection can also lead to [[chaos theory|dynamical chaos]] when some individuals' fitnesses become very low at intermediate allele frequencies.<ref>{{cite journal |last1=Altenberg |first1=Lee |title=Chaos from Linear Frequency-Dependent Selection |journal=American Naturalist |date=1991 |volume=138 |pages=51–68|doi=10.1086/285204 }}</ref><ref>{{cite journal | author1=Doebeli, Michael |author2=Ispolatov, Iaroslav |title=Chaos and unpredictability in evolution |journal=Evolution |date=2014 |volume=68 |issue=5 |pages=1365–1373|doi=10.1111/evo.12354 |pmid=24433364 |arxiv=1309.6261 |s2cid=12598843 }}</ref>

==Negative==
[[File:The anvil stone of a thrush - geograph.org.uk - 1751348.jpg|thumb|Anvil stone, where a thrush has broken open shells of polymorphic ''[[Cepaea]]'' snails; its selection of morphs may be frequency-dependent.<ref>{{cite journal |last1=Tucker |first1=G.M. |title=Apostatic selection by song thrushes (''Turdus philomelos'') feeding on the snail ''Cepaea hortensis'' |journal=Biological Journal of the Linnean Society |date=June 1991 |volume=43 |issue=2 |pages=149–156 |doi=10.1111/j.1095-8312.1991.tb00590.x}}</ref>]]

The first explicit statement of frequency-dependent selection appears to have been by [[Edward Bagnall Poulton]] in 1884, on the way that predators could maintain color polymorphisms in their prey.<ref>Poulton, E. B. 1884. Notes upon, or suggested by, the colours, markings and protective attitudes of certain lepidopterous larvae and pupae, and of a phytophagous hymenopterous larva. Transactions of the Entomological Society of London 1884: 27–60.</ref><ref>{{cite journal | last1 = Allen | first1 = J.A. | last2 = Clarke | first2 = B.C. | year = 1984 | title = Frequency-dependent selection -- homage to Poulton, E.B | journal = Biological Journal of the Linnean Society | volume = 23 | pages = 15–18 | doi=10.1111/j.1095-8312.1984.tb00802.x}}</ref>

Perhaps the best known early modern statement of the principle is [[Bryan Clarke]]'s 1962 paper on [[apostatic selection]] (a form of negative frequency-dependent selection).<ref>Clarke, B. 1962. Balanced polymorphism and the diversity of sympatric species. Pp. 47-70 in D. Nichols ed. Taxonomy and Geography. Systematics Association, Oxford.</ref> Clarke discussed predator attacks on polymorphic British snails, citing [[Luuk Tinbergen]]'s classic work on [[searching image]]s as support that predators such as birds tended to specialize in common forms of palatable species.<ref>Tinbergen, L. 1960. The natural control of insects in pinewoods. I. Factors influencing the intensity of predation in songbirds. Archs.Neerl.Zool. 13:265-343.</ref> Clarke later argued that frequency-dependent balancing selection could explain molecular polymorphisms (often in the absence of [[heterosis]]) in opposition to the [[neutral theory of molecular evolution]].<ref name=Kimura83>{{cite book |last=Kimura |first=Motoo |author-link=Motoo Kimura |date=1983 |title=The neutral theory of molecular evolution |publisher=Cambridge University Press |isbn=978-0-521-31793-1 }}</ref>

Another example is [[plant self-incompatibility]] [[allele]]s. When two plants share the same incompatibility allele, they are unable to mate. Thus, a plant with a new (and therefore, rare) allele has more success at mating, and its allele spreads quickly through the population.<ref>{{Cite journal |doi = 10.3389/fevo.2018.00010|title = Negative Frequency-Dependent Selection is Frequently Confounding|journal = Frontiers in Ecology and Evolution|volume = 6|year = 2018|last1 = Brisson|first1 = Dustin| page=10 |doi-access = free| pmid=34395455 |pmc = 8360343}}</ref>

A similar example is the csd alleles of the [[honey bee]]. A larva that is homozygous at csd is inviable. Therefore rare alleles spread through the population, pushing the gene pool toward an ideal equilibrium where every allele is equally common.<ref>{{Cite web|url=https://www.the-scientist.com/notebook/how-an-invasive-bee-managed-to-thrive-in-australia-32271|title=How an invasive bee managed to thrive in Australia|website=The Scientist Magazine®}}</ref>

The [[major histocompatibility complex]] (MHC) is involved in the recognition of foreign antigens and cells.<ref>{{cite journal | last1 = Takahata | first1 = N. | last2 = Nei | first2 = M. | date = 1990 | title = Allelic genealogy under overdominant and frequency-dependent selection and polymorphism of major histocompatibility complex loci | journal = Genetics | volume = 124 | issue = 4| pages = 967–78 | doi = 10.1093/genetics/124.4.967 | pmid = 2323559 | pmc = 1203987 }}</ref> Frequency-dependent selection may explain the high degree of polymorphism in the MHC.<ref>{{cite journal | last1 = Borghans | first1 = JA | last2 = Beltman | first2 = JB | last3 = De Boer | first3 = RJ. |date=Feb 2004 | title = MHC polymorphism under host-pathogen coevolution. | journal = Immunogenetics | volume = 55 | issue = 11| pages = 732–9 | doi=10.1007/s00251-003-0630-5 | pmid=14722687| hdl = 1874/8562 | s2cid = 20103440 | hdl-access = free }}</ref>

In [[behavioral ecology]], negative frequency-dependent selection often maintains multiple behavioral strategies within a species. A classic example is the Hawk-Dove model of interactions among individuals in a population. In a population with two traits A and B, being one form is better when most members are the other form.  As another example, male [[common side-blotched lizard]]s have three morphs, which either defend large territories and maintain large harems of females, defend smaller territories and keep one female, or mimic females in order to sneak matings from the other two morphs. These three morphs participate in a [[rock paper scissors]] sort of interaction such that no one morph completely outcompetes the other two.<ref name="S&L1996">{{cite journal |last=Sinervo |first=B. |author2=C.M. Lively |date=1996 |title=The rock–paper–scissors game and the evolution of alternative male strategies |journal=Nature |volume=380 |issue=6571 |pages=240–243 |doi=10.1038/380240a0|bibcode=1996Natur.380..240S |s2cid=205026253 }}</ref><ref name="Setal2000">{{cite journal |last=Sinervo |first=Barry |author2=Donald B. Miles |author3=W. Anthony Frankino |author4=Matthew Klukowski |author5=Dale F. DeNardo |date=2000 |title=Testosterone, Endurance, and Darwinian Fitness: Natural and Sexual Selection on the Physiological Bases of Alternative Male Behaviors in Side-Blotched Lizards |journal=Hormones and Behavior |volume=38 |issue=4 |pages=222–233 |doi=10.1006/hbeh.2000.1622 |pmid=11104640|s2cid=5759575 }}</ref> Another example occurs in the [[scaly-breasted munia]], where certain individuals become scroungers and others become producers.<ref>{{cite journal |last=Barnard |first=C.J.|author2=Sibly, R.M. |title=Producers and scroungers: A general model and its application to captive flocks of house sparrows |journal=Animal Behaviour |volume=29 |issue=2 |pages=543–550 |doi=10.1016/S0003-3472(81)80117-0|year=1981|s2cid=53170850}}</ref>



==Positive==
[[File:Müllerian mimicry among Heliconius species.tiff|thumb|Müllerian mimetic species of ''Heliconius'' from South America]]
[[File:G-Bartolotti SK.jpg|thumb|left|Harmless [[Lampropeltis elapsoides|scarlet kingsnake]] mimics the coral snake, but its pattern varies less where the coral snake is rare.]]
Positive frequency-dependent selection gives an advantage to common phenotypes. A good example is warning coloration in [[Aposematism|aposematic]] species.  Predators are more likely to remember a common color pattern that they have already encountered frequently than one that is rare. This means that new mutants or migrants that have color patterns other than the common type are eliminated from the population by differential predation.  Positive frequency-dependent selection provides the basis for [[Müllerian mimicry]], as described by Fritz Müller,<ref>{{cite journal |author=Müller, F. |author-link=Fritz Müller |year=1879 |title=Ituna and Thyridia; a remarkable case of mimicry in butterflies |journal=Proceedings of the Entomological Society of London |pages=20–29}}</ref> because all species involved are aposematic and share the benefit of a common, honest signal to potential predators.{{cn|date=May 2023}}

Another, rather complicated example occurs in the [[Batesian mimicry]] complex between a harmless mimic, the scarlet kingsnake (''[[Lampropeltis elapsoides]]''), and the model, the eastern coral snake (''[[Micrurus fulvius]]''), in locations where the model and mimic were in deep [[sympatry]], the [[phenotype]] of the scarlet kingsnake was quite variable due to relaxed selection. But where the pattern was rare, the predator population was not 'educated', so the pattern brought no benefit. The scarlet kingsnake was much less variable on the allopatry/sympatry border of the model and mimic, most probably due to increased selection since the eastern coral snake is rare, but present, on this border. Therefore, the coloration is only advantageous once it has become common.<ref name="Harper 1955–1961">{{cite journal |last=Harper |first=G. R. |author2=Pfennig, D. W. |title=Mimicry on the edge: why do mimics vary in resemblance to their model in different parts of their geographical range? |journal=Proceedings of the Royal Society B: Biological Sciences |date=22 August 2007 |volume=274 |issue=1621 |pages=1955–1961 |doi=10.1098/rspb.2007.0558 |pmid=17567563 |pmc=2275182}}</ref>

[[File:Coral snake.jpg|thumb|left|Venomous [[Micrurus fulvius|coral snake]]'s [[warning coloration]] can benefit [[Batesian mimicry|harmless mimic]]s, depending on their relative frequency.]]

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==See also==
* [[Apostatic selection]]
* [[Density dependence]]
* [[Evolutionary game theory]]
* [[Evolutionarily stable strategy]]
* [[Frequency-dependent foraging by pollinators]]
* [[Fluctuating selection]]
* [[Mimicry]]
* [[Tit for tat]]

== References ==
{{Reflist|30em}}

==Bibliography==
* [[Robert H. Tamarin]] (2001) ''Principles of Genetics''.  7th edition, McGraw-Hill.

{{DEFAULTSORT:Frequency-Dependent Selection}}

[[Category:Evolutionary biology concepts]]
[[Category:Population dynamics]]
[[Category:Selection]]