Stabilizing Selection


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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Stabilizing Selection

 

(also negative selection), a form of natural selection that is responsible for the preservation of the adaptive characteristics of organisms under constant environmental conditions. Stabilizing selection operates by means of the removal, or elimination, of individuals who deviate from the established norm. Therefore, under the influence of stabilizing selection, a population remains unchanged for a given characteristic, despite the continuous process of mutagenesis.

Stabilizing selection ensures the preservation of persistent and bradytelic forms, as well as the preservation during phylogeny of old characteristics that have not lost their adaptive significance. For example, the structure of the thyroid gland’s hormone —thyroxine—has remained unchanged throughout the evolution of vertebrate animals. According to I. I. Shmal’gauzen, who developed the concept of stabilizing selection, there is an increase in the genetic diversity of a population during stabilizing selection. Hence, recessive alleles accumulate when the phenotype is preserved unchanged, and, as a result, the gene pool of the population is enriched. Thus, a ready reserve of hereditary variation is formed, which constitutes the latent genotypic diversity of a population. The reserve becomes the material for evolution when there are sharp changes in the environment and evolutionary (positive) selection, which is the alternative to stabilizing selection, is put into action. Evolutionary and stabilizing selection always coexist in nature, and for any given period of a population’s evolution it is only possible to speak of the predominance of one of these forms.

An important result of stabilizing selection is the perfection of ontogenetic processes. Stabilizing selection accumulates hereditary changes that cause the rapid and reliable development of the constant characteristics of an adult organism that have been preserved. For this reason, both Shmal’gauzen and the British biologist C. Waddington regarded the evolutionary origin of adaptive modifications to be the result of stabilizing selection. If a population adapts simultaneously to different environmental conditions, several channels of ontogeny are formed on the basis of a given genotype. The channels, which are balanced complexes of mor-phogenetic processes, cause the development of a phenotype that is adapted to certain conditions.

In light of the effects of stabilizing selection, Waddington and the American biologist T. Dobzhansky have distinguished two subforms of stabilizing selection: normalizing selection, which preserves formed adaptations, and channelizing selection, under whose influence ontogeny is perfected.

REFERENCES

Shmal’gauzen, 1.1. Faktory evoliutsii, 2nd ed. Moscow, 1968.
Shmal’gauzen, 1.1. Problemy darvinizma, 2nd ed. Leningrad, 1969.
Dobzhansky, T. Genetics of the Evolutionary Process. New York-London, 1970.

A. S. SEVERTSOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
where W([z.sub.o]) is the relative fitness of an individual with phenotype [Z.sub.o], [[Beta].sub.o] is the directional selection gradient, [[Gamma].sub.o] (when negative) is the stabilizing selection gradient (also referred to as a nonlinear selection gradient, or quadratic selection gradient; Phillips and Arnold 1989; Brodie et al.
When females oviposit alone, there is stabilizing selection on the offspring sex ratio (Green et al.
cinerea reflects potentially stabilizing selection resulting from male-male competition and genetic, morphological, and functional integration.
Consider a functionally important, quantitative trait under Gaussian stabilizing selection. On a macroevolutionary time scale, the standard model from evolutionary quantitative genetics (Lande 1976, 1979) predicts an essentially instantaneous approach of the trait mean to its optimum.
These models also predict that benefits associated with resistance can offset these costs and yield stabilizing selection that produces an intermediate level of resistance.
In their model of stabilizing selection on a quantitative trait, peak shifts occur more rapidly if loci interact epistatically rather than additively in determining the trait value.
Under constant stabilizing selection opposed by random deleterious mutations negative covariance components evolve, because individuals with opposing allele effects (relative to the optimum) within or between loci will be closer to the optimum (Kimura 1965; Bulmer 1972, 1980; Lande 1976; Charlesworth 1990).
Stabilizing selection at this phylogenetic scale would have to be reconciled with the evidence for dietary and habitat partitioning among at least some of the species: andium, magister, limatus, and x.
This deviation increases with high gene flow (large [[Sigma].sup.2]), weak stabilizing selection (large [Omega]), ecological conditions that change rapidly in space (large b), and low heritability (small [h.sup.2]).
Predictors of evolvability under directional selection were higher than those for truncation or stabilizing selection. Evolvability estimates were considerably higher for date of flowering initiation and number of seeds per capsule than for date of last flowering.
Any strength of directional and stabilizing selection can be modeled by choosing appropriate values for [[Theta].sub.Y] and [w.sub.Y].
The forces of directional selection and stabilizing selection were estimated as the coefficients of the linear and quadratic terms, respectively, from regression analyses between relative feeding rate and bill depth (Lande and Arnold 1983).