Molecular evolution as predicted by natural selection

Valen, Leigh Van

doi:10.1007/bf01796554

Cited by 158 publications

(101 citation statements)

References 36 publications

(9 reference statements)

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“…But, similar to the bryozoan, colony growth and increasing inclusive fitness are two views of the same process. The component of fitness that is represented by both growth and the more diffuse increases in population size or inclusive fitness within a group has been called expansion, and supplements the reproductive and persistence components of fitness normally recognized [12,48,49]. Expansion is explicitly hierarchical; expansion at one level is traditional fitness at the level below [12].…”

Section: Discussionmentioning

confidence: 99%

The evolutionary history of division of labour

Simpson

2011

Proc. R. Soc. B.

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Functional specialization, or division of labour (DOL), of parts within organisms and colonies is common in most multi-cellular, colonial and social organisms, but it is far from ubiquitous. Several mechanisms have been proposed to explain the evolutionary origins of DOL; the basic feature common to all of them is that functional differences can arise easily. These mechanisms cannot explain the many groups of colonial and social animals that exhibit no DOL despite up to 500 million years of evolution. Here, I propose a new hypothesis, based on a multi-level selection theory, which predicts that a reproductive DOL is required to evolve prior to subsequent functional specialization. I test this hypothesis using a dataset consisting of the type of DOL for living and extinct colonial and social animals. The frequency distribution of DOL and the sequence of its acquisition confirm that reproductive specialization evolves prior to functional specialization. A corollary of this hypothesis is observed in colonial, social and also within multi-cellular organisms; those species without a reproductive DOL have a smaller range of internal variation, in terms of the number of polymorphs or cell types, than species with a reproductive DOL.

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Section: Discussionmentioning

confidence: 99%

The evolutionary history of division of labour

Simpson

2011

Proc. R. Soc. B.

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“…Eq. (Van Valen, 1974). Namely, 'It takes all the running in the step number space to keep the same Malthusian.'…”

Section: Red Queen Model and Critical Mutation Rates As A Simple Modementioning

confidence: 99%

A Synthetic Theory of Molecular Evolution.

Matsuda

Ishii

2001

Genes Genet. Syst.

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According to the neo-Darwinian view of evolution evolution rate v depends solely on the environment variation rate γ, whereas in the non-Darwinian view evolution rate is determined mainly by the mutation rate µ. We have studied two kinds of population genetics models which exhibit both types of evolution in different parametric regions: one is a dynamical model representing infinite population, and the other is a Markov process model representing a nearly monomorphic finite population. In the infinite population model, after proving general time-derivative and µ-derivative formulas for the population average of quantitative traits, we show that if the mutation rate is adaptively determined, µ must be larger than v in the stationary state. Loads of evolution are obtained in both regions. A high evolution rate such as v = 1 per genome per generation is consistent with Haldane's value of tolerable load if and only if the functional constraint is not large and selection is weak, independent of whether the evolution is neo-Darwinian or non-Darwinian. As the selection intensity increases, v is shown to change discontinuously from nearly µ to γ at the transition point. In the finite population model, the transition of v is not discontinuous, but is very steep. On the other hand, no steep change of polymorphism takes place at the transition point. The steepness of the transition in our model suggests that real molecular evolution can be divided into either neo-Darwinian or non-Darwinian, and that the intermediate type of evolution is rather rare.

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“…A long period of consolidation ensues for the species in this adaptive zone. Van Valen's "Red Queen" effect now takes over (24), and while the intensified competition, predation, and parasitism will doubtless encourage faster evolution at some loci, most loci, especially those concerned with energy and nutrient flow, will probably experience increasingly strict stabilizing selection.…”

Section: For Nearly Neutral Theory Population Size Mattersmentioning

confidence: 99%

Molecular clock rates at loci under stabilizing selection.

Foley

1987

Proc. Natl. Acad. Sci. U.S.A.

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Under stabilizing selection in a finite population, X, the rate of aflelic substitutions at a locus is approximately A ,I(1 + S)-'½, where iA is the mutation rate. S, the stringency of selection upon new mutants, is defined by SNVm/Vs, where N is the population size and Vm/Vs is a measure of the average fitness decrease experienced by new mutants. The approximation holds both for a "lonely" locus, which is the sole provider of genetic variation for the character under selection, and for an "embedded" locus, which is not. In both cases I use the Crow and Kimura model of a continuum of alleles with Gaussian selection and mutation. Monte Carlo simulations corroborate the substitution rate formula. Some molecular evolution data suggest the potential utility and limitations of the formula for estimating population size, mutation, and selection parameters. This work agrees with the rest of nearly neutral theory in emphasizing the important role of population size for substitution rates.Under a strictly neutral theory of molecular evolution, allelic substitutions would occur at an expected rate of X = 2Nguu(1/2N) = g, [1] where X is the substitution rate, ,u is the mutation rate, N is the population size, and u(1/2N) is the substitution probability. Under a less strict, effectively neutral theory, one could expect [2] where p is the rate of appearance of neutral mutants, and p > p (1). But this model, which corresponds to Kimura's original proposal, depends on the deleterious mutants being so bad that they have no chance of becoming fixed. Meanwhile, new neutral alleles must have substitution probability 1/2N for Eq. 2 to work exactly. Thus, Ohta (2), Kimura (3), and others (4-7) have developed more sophisticated nearly neutral models in which new mutants can assume any of a continuum of selection coefficients. The effectively neutral mutation rate might then be defined, as in ref. 3, by the rate of mutations to alleles with a selection coefficient less than 1/2N. Kimura (3), for example, showed that Eq. 2 holds approximately when selection coefficients are distributed according to a Gamma density.Most students of natural selection agree that at the phenotypic level, stabilizing selection rules. In this paper, I obtain an approximation for X, when the locus of interest is at equilibrium under stabilizing selection. The present work builds on the work of Kimura (8) in which the nearly neutral theory was first extended to this important special case.I show that the approximation is fairly robust to deviations from the assumptions of the model that engenders it. Monte Carlo simulations using a variant of the pseudosamplingvariable method of Kimura and Takahata (9) also corroborate the analytic results. The substitution rate formula can be used, with some discretion, to investigate DNA sequencedivergence data. Two Models with a Continuum of Possible AllelesCrow and Kimura (10) introduced a model for the study of quantitative characters under stabilizing selection that has since been put to considerable use (11,12)....

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Molecular evolution as predicted by natural selection

Cited by 158 publications

References 36 publications

The evolutionary history of division of labour

The evolutionary history of division of labour

A Synthetic Theory of Molecular Evolution.

Molecular clock rates at loci under stabilizing selection.

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