Frequency-dependent selection
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Frequency-dependent selection is an evolutionary process by which the fitness of a
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
or
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
depends on the phenotype or genotype composition of a given
population Population typically refers to the number of people in a single area, whether it be a city or town, region, country, continent, or the world. Governments typically quantify the size of the resident population within their jurisdiction using a ...
. * In positive frequency-dependent selection, the fitness of a phenotype or
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
increases as it becomes more common. * In negative frequency-dependent selection, the fitness of a phenotype or
genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...
decreases as it becomes more common. This is an example of
balancing selection Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. Balancing ...
. * 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. 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 Anti-predator adaptations are mechanisms developed through evolution that assist prey organisms in their constant struggle against predators. Throughout the animal kingdom, adaptations have evolved for every stage of this struggle, namely by avo ...
. Frequency-dependent selection can lead to 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''ij parameters in Lotka-Volterra competition equations are non-zero). Frequency-dependent selection can also lead to dynamical chaos when some individuals' fitnesses become very low at intermediate allele frequencies.


Negative

The first explicit statement of frequency-dependent selection appears to have been by
Edward Bagnall Poulton Sir Edward Bagnall Poulton, FRS HFRSE FLS (27 January 1856 – 20 November 1943) was a British evolutionary biologist, a lifelong advocate of natural selection through a period in which many scientists such as Reginald Punnett doubted its i ...
in 1884, on the way that predators could maintain color polymorphisms in their prey. Perhaps the best known early modern statement of the principle is
Bryan Clarke Bryan Campbell Clarke (24 June 1932 – 27 February 2014) was a British Professor of genetics, latterly emeritus at the University of Nottingham. Clarke is particularly noted for his work on apostatic selection (which is a term he coined ...
's 1962 paper on
apostatic selection Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different (through mutation) from their species in a way that makes it more likely for them to be ignored by the ...
(a synonym of negative frequency-dependent selection). Clarke discussed predator attacks on polymorphic British snails, citing
Luuk Tinbergen Luuk Tinbergen (7 September 1915, in The Hague – 1 September 1955, in Groningen) was a Dutch ornithologist and ecologist. Tinbergen was the youngest of three eminent brothers — both Jan and Nikolaas won Nobel Prizes, for economics an ...
's classic work on searching images as support that predators such as birds tended to specialize in common forms of palatable species. Clarke later argued that frequency-dependent balancing selection could explain molecular polymorphisms (often in the absence of
heterosis Heterosis, hybrid vigor, or outbreeding enhancement is the improved or increased function of any biological quality in a hybrid offspring. An offspring is heterotic if its traits are enhanced as a result of mixing the genetic contributions of ...
) in opposition to the
neutral theory of molecular evolution The neutral theory of molecular evolution holds that most evolutionary changes occur at the molecular level, and most of the variation within and between species are due to random genetic drift of mutant alleles that are selectively neutral. The ...
. Another example is
plant self-incompatibility Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals ...
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
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. Another similar example is csd alleles of
honey bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current co ...
. 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. The
major histocompatibility complex The major histocompatibility complex (MHC) is a large locus on vertebrate DNA containing a set of closely linked polymorphic genes that code for cell surface proteins essential for the adaptive immune system. These cell surface proteins are calle ...
(MHC) is involved in the recognition of foreign antigens and cells. Frequency-dependent selection may explain the high degree of polymorphism in the MHC. In
behavioral ecology Behavioral ecology, also spelled behavioural ecology, is the study of the evolutionary basis for animal behavior due to ecological pressures. Behavioral ecology emerged from ethology after Niko Tinbergen outlined four questions to address when ...
, 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 The common side-blotched lizard (''Uta stansburiana'') is a species of side-blotched lizard in the family Phrynosomatidae. The species is native to dry regions of the western United States and northern Mexico. It is notable for having a unique fo ...
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 Rock paper scissors (also known by other orderings of the three items, with "rock" sometimes being called "stone," or as Rochambeau, roshambo, or ro-sham-bo) is a hand game originating in China, usually played between two people, in which each p ...
sort of interaction such that no one morph completely outcompetes the other two. Another example occurs in the
scaly-breasted munia The scaly-breasted munia or spotted munia (''Lonchura punctulata''), known in the pet trade as nutmeg mannikin or spice finch, is a sparrow-sized estrildid finch native to tropical Asia. A species of the genus ''Lonchura'', it was formally desc ...
, where certain individuals become scroungers and others become producers. A common misconception is that negative frequency-dependent selection causes the genetic diversity of influenza haemagglutinin (HA) glycoproteins. This is not an example of negative frequency-dependent selection. This is because the rate at which a particular influenza strain will spread is linked to absolute abundance, not relative abundance.


Positive

Positive frequency-dependent selection gives an advantage to common phenotypes. A good example is warning coloration in
aposematic Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste or ...
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 Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimic each other's honest warning signals, to their mutual benefit. The benefit to Müllerian ...
, as described by Fritz Müller, because all species involved are aposematic and share the benefit of a common, honest signal to potential predators. Another, rather complicated example occurs in the
Batesian mimicry Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, after his work on bu ...
complex between a harmless mimic, the scarlet kingsnake (''
Lampropeltis elapsoides The scarlet kingsnake or scarlet milk snake (''Lampropeltis elapsoides'') is a species of kingsnake found in the southeastern and eastern portions of the United States. Like all kingsnakes, they are venomous snake, nonvenomous. They are found in ...
''), and the model, the eastern coral snake (''
Micrurus fulvius ''Micrurus fulvius'', commonly known as the eastern coral snake,John L. Behler, Behler John L.; King, F. Wayne (1979). ''The Audubon Society Field Guide to North American Reptiles and Amphibians''. New York: Alfred A. Knopf. 743 pp., 657 color ...
''), in locations where the model and mimic were in deep
sympatry In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
, the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
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.


See also

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Apostatic selection Apostatic selection is a form of negative frequency-dependent selection. It describes the survival of individual prey animals that are different (through mutation) from their species in a way that makes it more likely for them to be ignored by the ...
*
Evolutionary game theory Evolutionary game theory (EGT) is the application of game theory to evolving populations in biology. It defines a framework of contests, strategies, and analytics into which Darwinian competition can be modelled. It originated in 1973 with John Ma ...
*
Evolutionarily stable strategy An evolutionarily stable strategy (ESS) is a strategy (or set of strategies) that is ''impermeable'' when adopted by a population in adaptation to a specific environment, that is to say it cannot be displaced by an alternative strategy (or set of ...
*
Frequency-dependent foraging by pollinators Frequency-dependent foraging is defined as the tendency of an individual to selectively forage on a certain species or morph based on its relative frequency within a population.Levin 1972. Low frequency disadvantage in the exploitation of pollin ...
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Fluctuating Selection Fluctuating selection is a mode of natural selection characterized by the fluctuation of the direction of selection on a given phenotype over a relatively brief period of evolutionary time. For example, a species of plant may come in two varieties ...
*
Mimicry In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. Often, mimicry f ...
*
Tit for tat Tit for tat is an English saying meaning "equivalent retaliation". It developed from "tip for tap", first recorded in 1558. It is also a highly effective strategy in game theory. An agent using this strategy will first cooperate, then subseque ...


References


Bibliography

* Robert H. Tamarin (2001) ''Principles of Genetics''. 7th edition, McGraw-Hill. {{DEFAULTSORT:Frequency-Dependent Selection Evolutionary biology concepts Population dynamics Selection