Frequency-dependent selection, metrical characters and molecular evolution

1988 ◽  
Vol 319 (1196) ◽  
pp. 631-640 ◽  
Keyword(s):  
Molecular Evolution ◽  
Genetic Drift ◽  
Random Order ◽  
Quantitative Character ◽  
Stabilizing Selection ◽  
Molecular Clocks ◽  
Random Genetic Drift ◽  
Stochastic Effects ◽  
Frequency Dependent ◽  
Frequency Dependent Selection

Computer models of selection acting on a quantitative character show that a combination of frequency-dependent and stabilizing selection can maintain many polymorphisms among the genes that determine the character. The models also show that the random order of mutations can give rise to selectively driven stochastic effects that are sometimes more important than random genetic drift. They suggest simple explanations for patterns of divergence between populations and species, and for apparent discrepancies between the rates of morphological and molecular evolution. They point towards a selective theory of ‘molecular clocks’

Isolation by distance in a quantitative trait.

Genetics ◽  
1991 ◽  
Vol 128 (2) ◽  
pp. 443-452 ◽  
Author(s):  
R Lande
Keyword(s):  
Genetic Drift ◽  
Genetic Variance ◽  
Two Dimensions ◽  
Quantitative Character ◽  
Stabilizing Selection ◽  
Neighborhood Size ◽  
Phenotypic Variance ◽  
Two Dimensional ◽  
Random Genetic Drift ◽  
Dispersal Function

Abstract Random genetic drift in a quantitative character is modeled for a population with a continuous spatial distribution in an infinite habitat of one or two dimensions. The analysis extends Wright's concept of neighborhood size to spatially autocorrelated sampling variation in the expected phenotype at different locations. Weak stabilizing selection is assumed to operate toward the same optimum phenotype in every locality, and the distribution of dispersal distances from parent to offspring is a (radially) symmetric function. The equilibrium pattern of geographic variation in the expected local phenotype depends on the neighborhood size, the genetic variance within neighborhoods, and the strength of selection, but is nearly independent of the form of the dispersal function. With all else equal, geographic variance is smaller in a two-dimensional habitat than in one dimension, and the covariance between expected local phenotypes decreases more rapidly with the distance separating them in two dimensions than in one. The equilibrium geographic variance is less than the phenotypic variance within localities, unless the neighborhood size is small and selection is extremely weak, especially in two dimensions. Nevertheless, dispersal of geographic variance created by random genetic drift is an important mechanism maintaining genetic variance within local populations. For a Gaussian dispersal function it is shown that, even with a small neighborhood size, a population in a two-dimensional habitat can maintain within neighborhoods most of the genetic variance that would occur in an infinite panmictic population.

A model of quantitative traits under frequency-dependent balancing selection

1990 ◽  
Vol 240 (1297) ◽  
pp. 15-28 ◽  
Keyword(s):  
Computer Model ◽  
Quantitative Traits ◽  
Balancing Selection ◽  
Quantitative Character ◽  
Stabilizing Selection ◽  
Neutral Model ◽  
Frequency Dependent ◽  
Frequency Dependent Selection ◽  
Precise Form ◽  
Natural Variations

We describe a computer model that stimulates a combination of stabilizing and frequency-dependent selection acting on a quantitative character determined by several loci. The results correspond to many features of natural variations at both the phenotypic and genotypic levels. The model is robust, and its results are not strongly dependent either on the nature and shape of the function describing the stabilizing selection, or on the precise form of frequency dependence, except near the extrema. It suggests a mechanism for the maintenance of large amounts of variability, and shows a relation between population size and heterozygosity roughly corresponding to that found in nature. In this respect it is unlike the purely neutral model.

scholarly journals Genetic loads at a polymorphic locus which is maintained by frequency-dependent selection

1970 ◽  
Vol 16 (2) ◽  
pp. 145-150 ◽  
Author(s):  
Motoo Kimura ◽  
Tomoko Ohta
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Genetic Drift ◽  
Gene Frequency ◽  
Polymorphic Locus ◽  
Small Populations ◽  
Effective Population ◽  
Frequency Dependent ◽  
Frequency Dependent Selection ◽  
Selective Neutrality

SUMMARYIf a polymorphic locus is maintained in finite populations by frequency-dependent selection with selective neutrality at equilibrium, it is generally accompanied by two genetic loads, i.e. the dysmetric and the drift loads. The former arises because the fitness of the population may not be at a maximum at the equilibrium gene frequency and the latter because genetic drift in small populations displaces the gene frequency from its equilibrium value.In some simple models of frequency-dependent selection considered, the drift load is independent of selection coefficients and is approximately equal to (n−1)/(2Ne), where n is the number of alleles and Ne is the effective population size.

scholarly journals THE SELECTIVE VALUE OF ALLELES UNDERLYING POLYGENIC TRAITS

Genetics ◽  
1984 ◽  
Vol 108 (4) ◽  
pp. 1021-1033
Author(s):  
Michael Lynch
Keyword(s):  
Molecular Evolution ◽  
Genetic Drift ◽  
Genetic Variance ◽  
Neutral Theory ◽  
Mechanistic Explanation ◽  
Neutral Evolution ◽  
Stabilizing Selection ◽  
Average Effect ◽  
Absolute Value ◽  
The Mean

ABSTRACT To define the genetic and ecological circumstances that are conductive to evolution via genetic drift at the allelic level, the selection coefficient for a constituent allele of arbitrary effect is derived for a polygenic character exposed to stabilizing selection. Under virtually all possible conditions, alleles within the class for which the absolute value of the average effect is <10-2 phenotypic standard deviations are neutral with respect to each other. In addition, when the mean phenotype is at the optimum and the genetic variance is in selection-drift-mutation equilibrium, a considerable amount of neutral evolution is expected in the class of alleles with intermediate effects on the phenotype. These results help clarify how molecular evolution via genetic drift may occur at a locus despite intense selection and provide a potential mechanistic explanation for the neutral theory of molecular evolution.

Mutational order: a major stochastic process in evolution

1990 ◽  
Vol 240 (1297) ◽  
pp. 29-37 ◽  
Keyword(s):  
Stochastic Process ◽  
Computer Simulations ◽  
Genetic Drift ◽  
Molecular Clock ◽  
Quantitative Character ◽  
Evolutionary Divergence ◽  
Random Genetic Drift ◽  
Random Drift ◽  
Large Populations ◽  
Different Populations

Computer simulations in which selection acts on a quantitative character show that the randomness of mutations can contribute significantly to evolutionary divergence between populations. In different populations, different advantageous mutations occur, and are selected to fixation, so that the populations diverge even when they are initially identical, and are subject to identical selection. This stochastic process is distinct from random genetic drift. In some circumstances (large populations or strong selection, or both) mutational order can be greatly more important than random drift in bringing about divergence. It can generate a ‘disconnection’ between evolution at the phenotypic and genotypic levels, and can give rise to a rough ‘molecular clock’, albeit episodic, that is driven by selection. In the absence of selection, mutational order has little or no effect.

scholarly journals A White Noise Approach to Evolutionary Ecology

2020 ◽  
Author(s):  
Bob Week ◽  
Scott L. Nuismer ◽  
Luke J. Harmon ◽  
Stephen M. Krone
Keyword(s):  
White Noise ◽  
Genetic Drift ◽  
Evolutionary Ecology ◽  
Quantitative Character ◽  
Random Genetic Drift ◽  
Demographic Stochasticity ◽  
Selection Gradients ◽  
Evolutionary Response ◽  
Linear Selection ◽  
The Relationship

AbstractAlthough the evolutionary response to random genetic drift is classically modelled as a sampling process for populations with fixed abundance, the abundances of populations in the wild fluctuate over time. Furthermore, since wild populations exhibit demographic stochasticity, it is reasonable to consider the evolutionary response to demographic stochasticity and its relation to random genetic drift. Here we close this gap in the context of quantitative genetics by deriving the dynamics of the distribution of a quantitative character and the abundance of a biological population from a stochastic partial differential equation driven by space-time white noise. In the process we develop a useful set of heuristics to operationalize the powerful, but abstract theory of white noise and measure-valued stochastic processes. This approach allows us to compute the full implications of demographic stochasticity on phenotypic distributions and abundances of populations. We demonstrate the utility of our approach by deriving a quantitative genetic model of diffuse coevolution mediated by exploitative competition for a continuum of resources. In addition to trait and abundance distributions, this model predicts interaction networks defined by rates of interactions, competition coefficients, or selection gradients. Analyzing the relationship between selection gradients and competition coefficients reveals independence between linear selection gradients and competition coefficients. In contrast, absolute values of linear selection gradients and quadratic selection gradients tend to be positively correlated with competition coefficients. That is, competing species that strongly affect each other’s abundance tend to also impose selection on one another, but the directionality is not predicted. This approach contributes to the development of a synthetic theory of evolutionary ecology by formalizing first principle derivations of stochastic models that underlie rigorous investigations of the relationship between feedbacks of biological processes and the patterns of diversity they produce.

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