Mutational order: a major stochastic process in evolution

Mani, G.S.; Clarke, Bryan

doi:10.1098/rspb.1990.0025

Cited by 159 publications

(89 citation statements)

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“…Both of these processes may reflect lack of consistent local adaptation among populations of C. fasciculata that we observed at the scale of Յ 100 km (Galloway and Fenster 2000). Another stochastic process, the random incorporation of novel mutations across populations that have epistatic effects on subsequent mutations (Mani and Clarke 1990), may also give rise to the observed loss of fitness in FIG. 9.…”

Section: Population Divergence and The Interaction Among Selection Dmentioning

confidence: 99%

Population Differentiation in an Annual Legume: Genetic Architecture

Fenster¹,

Galloway²

2000

Evolution

217

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Abstract. The presence or absence of epistasis, or gene interaction, is explicitly assumed in many evolutionary models. Although many empirical studies have documented a role of epistasis in population divergence under laboratory conditions, there have been very few attempts at quantifying epistasis in the native environment where natural selection is expected to act. In addition, we have little understanding of the frequency with which epistasis contributes to the evolution of natural populations. In this study we used a quantitative genetic design to quantify the contribution of epistasis to population divergence for fitness components of a native annual legume, Chamaecrista fasciculata. The design incorporated the contrast of performance of F 2 and F 3 segregating progeny of 18 interpopulation crosses with the F 1 and their parents. Crosses were conducted between populations from 100 m to 2000 km apart. All generations were grown for two seasons in the natural environment of one of the parents. The F 1 often outperformed the parents. This F 1 heterosis reveals population structure and suggests that drift is a major contributor to population differentiation. The F 2 generation demonstrated that combining genes from different populations can sometimes have unexpected positive effects. However, the F 3 performance indicated that combining genes from different populations decreased vigor beyond that due to the expected loss of heterozygosity. Combined with previous data, our results suggest that both selection and drift contribute to population differentiation that is based on epistatic genetic divergence. Because only the F 3 consistently expressed hybrid breakdown, we conclude that the epistasis documented in our study reflects interactions among linked loci.

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Section: Population Divergence and The Interaction Among Selection Dmentioning

confidence: 99%

Population Differentiation in an Annual Legume: Genetic Architecture

Fenster¹,

Galloway²

2000

Evolution

217

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“…1). In contrast, under mutation-order speciation (7,11), populations diverge as they accumulate a different series of mutations under similar selection pressures (Fig. 1).…”

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Genetics and ecological speciation

Schluter

Conte

2009

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

557

616

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Species originate frequently by natural selection. A general mechanism by which this occurs is ecological speciation, defined as the evolution of reproductive isolation between populations as a result of ecologically-based divergent natural selection. The alternative mechanism is mutation-order speciation in which populations fix different mutations as they adapt to similar selection pressures. Although numerous cases now indicate the importance of ecological speciation in nature, very little is known about the genetics of the process. Here, we summarize the genetics of premating and postzygotic isolation and the role of standing genetic variation in ecological speciation. We discuss the role of selection from standing genetic variation in threespine stickleback (Gasterosteus aculeatus), a complex of species whose ancestral marine form repeatedly colonized and adapted to freshwater environments. We propose that ecological speciation has occurred multiple times in parallel in this group via a ''transporter'' process in which selection in freshwater environments repeatedly acts on standing genetic variation that is maintained in marine populations by export of freshwater-adapted alleles from elsewhere in the range. Selection from standing genetic variation is likely to play a large role in ecological speciation, which may partly account for its rapidity.reproductive isolation ͉ stickleback ͉ standing genetic variation ͉ transporter hypothesis O ne of Darwin's greatest ideas was that new species originate by natural selection (1). It has taken evolutionary biologists almost until now to realize that he was probably correct. Darwin looked at species mainly as sets of individuals closely resembling each other (1), in which case adaptive divergence in phenotype eventually leads to speciation almost by definition. Later, Dobzhansky (2) and Mayr (3) defined species and speciation by the criterion of reproductive isolation instead. Recent evidence indicates that reproductive isolation also evolves frequently by natural selection (4-7).Speciation by natural selection occurs by 2 general mechanisms (4, 7). The first of these is ecological speciation, defined as the evolution of reproductive isolation between populations, or subsets of a single population, as a result of ecologically-based divergent natural selection (6,(8)(9)(10). Under this process natural selection acts in contrasting directions between environments, which drives the fixation of different alleles each advantageous in one environment but not in the other (Fig. 1). In contrast, under mutation-order speciation (7, 11), populations diverge as they accumulate a different series of mutations under similar selection pressures (Fig. 1). Natural selection drives alleles to fixation in both speciation mechanisms, but selection favors divergence only under ecological speciation. Divergence occurs by chance under the mutation-order process.There is growing evidence in support of both ecological and mutation-order speciation in nature (4, 7), yet numerous aspects of ...

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“…A mutation that is beneficial at the time of its introduction may confer its beneficial effect only in the presence of other potentiating or permissive mutations (1)(2)(3)(4)(5)(6)(7)(8)(9). Thus, the fate of a mutation arising in a population may be contingent on previous mutations (10)(11)(12)(13). Conversely, once a mutation has fixed in a population, the mutation becomes part of the genetic background onto which subsequent modifications are introduced.…”

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Contingency and entrenchment in protein evolution under purifying selection

Shah

McCandlish

Plotkin

2015

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

183

236

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The phenotypic effect of an allele at one genetic site may depend on alleles at other sites, a phenomenon known as epistasis. Epistasis can profoundly influence the process of evolution in populations and shape the patterns of protein divergence across species. Whereas epistasis between adaptive substitutions has been studied extensively, relatively little is known about epistasis under purifying selection. Here we use computational models of thermodynamic stability in a ligand-binding protein to explore the structure of epistasis in simulations of protein sequence evolution. Even though the predicted effects on stability of random mutations are almost completely additive, the mutations that fix under purifying selection are enriched for epistasis. In particular, the mutations that fix are contingent on previous substitutions: Although nearly neutral at their time of fixation, these mutations would be deleterious in the absence of preceding substitutions. Conversely, substitutions under purifying selection are subsequently entrenched by epistasis with later substitutions: They become increasingly deleterious to revert over time. Our results imply that, even under purifying selection, protein sequence evolution is often contingent on history and so it cannot be predicted by the phenotypic effects of mutations assayed in the ancestral background.intragenic epistasis | coevolution | near neutrality | protein stability W hether a heritable mutation is advantageous or deleterious to an organism often depends on the evolutionary history of the population. A mutation that is beneficial at the time of its introduction may confer its beneficial effect only in the presence of other potentiating or permissive mutations (1-9). Thus, the fate of a mutation arising in a population may be contingent on previous mutations (10-13). Conversely, once a mutation has fixed in a population, the mutation becomes part of the genetic background onto which subsequent modifications are introduced. Because the beneficial effects of the subsequent modifications may depend on the focal mutation, as time passes reversion of the focal mutation may become increasingly deleterious, leading to a type of evolutionary conservatism, or entrenchment (14-18).In the context of protein evolution, the effects of contingency and entrenchment are most easily studied by considering a sequence of single amino acid changes (19) that extends both forward and backward in time from some focal substitution. To assess the roles of contingency and entrenchment we can study the degree to which each focal substitution was facilitated by previous substitutions, and the degree to which the focal substitution influences the subsequent course of evolution (Fig. 1A).Dependencies within a sequence of substitutions are closely connected to the concept of epistasis-that is, the idea that the phenotypic effect of a mutation at a particular genetic site may depend on the genetic background in which it arises (20-24). In the absence of epistasis, a mutation has the same effect ...

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Mutational order: a major stochastic process in evolution

Cited by 159 publications

References 16 publications

Population Differentiation in an Annual Legume: Genetic Architecture

Population Differentiation in an Annual Legume: Genetic Architecture

Genetics and ecological speciation

Contingency and entrenchment in protein evolution under purifying selection

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