Mutations for polygenic traits in barley under nutrient stress

Cox, T. S.; Cox, D. J.; Frey, K. J.

doi:10.1007/bf00051866

Cited by 7 publications

(5 citation statements)

References 4 publications

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“…Deng and Lynch (1997) estimated V m /V E for mean clutch size to be 8.9 ϫ 10 Ϫ4 and 3.4 ϫ 10 Ϫ5 in Daphnia pulicaria and Daphnia arenata, respectively. Lynch (1988) analyzed data published by Cox et al (1987) to estimate V m /V E for grain yield in barley at Ͻ 1 ϫ 10 Ϫ4 in highnutrient conditions and 4 ϫ 10 Ϫ4 in low-nutrient conditions. Our estimates of V m ϭ 3.5 ϫ 10 Ϫ3 and V m /V E ϭ 4.6 ϫ 10 Ϫ3 per generation may be comparable with Houle's results (depending upon the magnitude of V E for fitness in Drosophila), but are about four times greater than the estimates reported for Daphnia pulex and clutch size in D. pulicaria and an order of magnitude greater than estimates for viability in Drosophila, mean clutch size in D. arenata, and grain yield in barley.…”

Section: Discussionmentioning

confidence: 99%

The Ecology and Genetics of Fitness in Chlamydomonas. Ix. The Rate of Accumulation of Variation of Fitness Under Selection

Goho

Bell

2000

Evolution

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Populations of Chlamydomonas founded by single cells were cultured in chemostats for 50 days, representing about 125 generations. The mean and variance of division rate was measured daily by withdrawing cells from the effluent and culturing them for 24 h on filtered effluent medium solidified with agar. Mean fitness did not change during the period of culture, and the behavior of neutral markers indicated that no substitutions of novel beneficial mutations occurred. However, the variance of fitness increased markedly at about the same rate in two replicate populations. The standardized rate, or mutational heritability, was Vm/VE = 4-5 x 10(-3) per generation. This is substantially greater than most other estimates for characters closely correlated with fitness. Moreover, it seems difficult to reconcile with the absence of any change in mean fitness. We investigated the possibility that frequency-dependent selection was created by spatial heterogeneity within the culture vessel by testing cell populations with different phenotypes from the top, bottom, and surface of the chemostats. However, the differentiation of these populations seemed to be attributable to phenotypic plasticity, with no evidence that their characteristics were heritable. Finally, we report an experiment in which lines were selected for about 100 generations on solid or liquid medium. These lines became specifically adapted to the medium on which they were cultured, showing that liquid and solid media, even when chemically identical, provide different conditions of growth for Chlamydomonas. The genetic variance appearing in the cultures was therefore attributed to conditionally neutral mutations that were not expressed in the chemostat. This implies that rates of accumulation of mutational variance measured in the culture environment itself (where this can be done) may greatly underestimate the variation available for a response through selection to environmental change. Moreover, it suggests that chemostat populations may be more dynamic and more diverse than is usually thought.

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Section: Discussionmentioning

confidence: 99%

The Ecology and Genetics of Fitness in Chlamydomonas. Ix. The Rate of Accumulation of Variation of Fitness Under Selection

Goho

Bell

2000

Evolution

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“…The two types of studies are therefore in rough accord. Cox et al (1987) recently completed an experiment with three inbred lines of barley grown at two nutrient levels following the design of Russell et al (1963) In their table 3, the authors record successive variance components for new sublines within lines. The expectation of each of these is 2V m .…”

Section: (Vii) Corn Vegetative and Reproductive Traitsmentioning

confidence: 99%

“…The expectation of each of these is 2V m . The sampling variance of mean phenotypes is reported in Table 2 (Cox et al 1987) as Error (b); multiplication of these by the sample size (30) generates estimates of V E . The resultant estimates of V m /V E for biomass (00001 and 00004) and grain (< 00001 and 00004) yield are quite low, the higher estimates arising under low nutrient conditions.…”

Section: (Vii) Corn Vegetative and Reproductive Traitsmentioning

confidence: 99%

The rate of polygenic mutation

1988

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By application of the neutral model of phenotypic evolution, quantitative estimates of the rate of input of genetic variance by polygenic mutation can be extracted from divergence experiments as well as from the response of an inbred base population to selection. The analytical methods are illustrated through a survey of data on a diversity of organisms including Drosophila, Tribolium, mice, and several crop species. The mutational rate of introduction of genetic variance (V m ) scaled by the environmental variance (V E ) is shown to vary between populations, species, and characters with a range of approximately 10~4 to 5 x 10" 2 . V m /V E for Drosophila viability is somewhat below this range, while hybrid dysgenesis may temporarily inflate V m /V E beyond 10" 1 . Potential sources of bias and error in" the estimation of V m are discussed, as are the practical implications of the observed limits to VJ V B for projecting the long-term response to selection and for testing adaptational hypotheses.

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“…The environmental difference in this case was relatively small, however. Cox et al (1987) allowed mutations to accumulate for six generations in barley cultivars, and found no evidence for GEl for biomass and grain yield when the lines were tested in high and low nutrient environments. Variation among the lines in this experiment appears to have been relatively slight, however, as might be expected from only six generations of mutation accumulation.…”

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confidence: 98%

THE CONTRIBUTION OF NEW MUTATIONS TO GENOTYPE‐ENVIRONMENT INTERACTION FOR FITNESS IN DROSOPHILA MELANOGASTER

1996

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Many studies have documented the existence of genotype-environment interaction (GEI) for traits closely related to fitness in natural populations. A type of GEI that is commonly observed is changes in the fitness ranking of genetic groups (families, clones, or inbred lines) in different environments. We refer to such changes in ranking as crossing of reaction norms for fitness. A common interpretation of crossing of reaction norms for fitness is that selection favors different alleles in the different environments (i.e., that "trade-offs" exist). If this is the case, selection could maintain genetic variation, and even lead to reproductive isolation between subpopulations using different environments. Even if the same alleles are favored in every environment, however, deleterious mutations that vary in the magnitude of their effect depending on environment could cause reaction norms for fitness to cross. If deleterious mutations with environment-dependent effects are responsible for maintaining much of the variation leading to crossing of reaction norms for fitness in natural populations, it should be possible to observe crossing of reaction norms for fitness among otherwise genetically identical lines bearing newly arisen spontaneous mutations. We examined the contribution of new mutations to GEI for fitness in Drosophila melanogaster. Eighteen lines were derived from a common, highly inbred base stock, and maintained at a population size of 10 pairs for over 200 generations, to allow them to accumulate spontaneous mutations. Because of the small population size of the lines, selection against mildly deleterious mutations should have been relatively ineffective. The lines were tested for productivity (number of surviving adult progeny from a standard number of parents) in five different environmental treatments, comprising different food media, temperatures, and levels of competition. The lines showed highly significant GEI for productivity, owing largely to considerable changes in ranking in the different environments. We conclude that mutations that are deleterious on average, but whose quantitative effects depend on environment, could be responsible for maintaining much of the variation leading to crossing of reaction norms for fitness that has been observed in samples of D. melanogaster from the wild.

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Mutations for polygenic traits in barley under nutrient stress

Cited by 7 publications

References 4 publications

The Ecology and Genetics of Fitness in Chlamydomonas. Ix. The Rate of Accumulation of Variation of Fitness Under Selection

The Ecology and Genetics of Fitness in Chlamydomonas. Ix. The Rate of Accumulation of Variation of Fitness Under Selection

The rate of polygenic mutation

THE CONTRIBUTION OF NEW MUTATIONS TO GENOTYPE‐ENVIRONMENT INTERACTION FOR FITNESS IN DROSOPHILA MELANOGASTER

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