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Spencer C. H. Barrett - One of the best experts on this subject based on the ideXlab platform.

Christopher G. Eckert - One of the best experts on this subject based on the ideXlab platform.

Domenica Manicacci - One of the best experts on this subject based on the ideXlab platform.

Christopher C. Mundt - One of the best experts on this subject based on the ideXlab platform.

  • Impact of density and disease on Frequency-Dependent Selection and genetic polymorphism: experiments with stripe rust and wheat
    Evolutionary Ecology, 2008
    Co-Authors: Christopher C. Mundt, Johanne Brunet, Kathryn E. Sackett
    Abstract:

    Frequency-Dependent disease impacts may contribute to the maintenance of genetic diversity and sexual reproduction in plant populations. In earlier work with experimental wheat ( Triticum aestivum ) populations at a single density, we found that stripe rust (caused by Puccinia striiformis ) created Frequency-Dependent Selection on its host but competitive interactions between host genotypes reduced the potential for disease to maintain genetic polymorphisms in this highly self-pollinated species; the weaker competitor actually exhibited positive disease-mediated Frequency-Dependent Selection. Based on these results we predicted that at low density, where the overall level of competition is lower, disease would have a stronger impact relative to competition and thus be more likely to maintain genetic polymorphisms; at low densities the greatest effect of disease for negative Frequency-Dependent Selection should be seen in the weak competitor. Here we report on results with wheat stripe rust in which we altered both the Frequency and density of host genotypes in factorial combinations of two-way mixtures where each host genotype was attacked by its own specialized race of rust. Within each density disease levels increased with genotype frequencies, creating Frequency-Dependent disease attack at all densities. Similarly, disease created negative Frequency-Dependent Selection on its host at all densities, as a genotype’s fitness was often greater at low than high Frequency when disease was present. Disease levels increased with plant density in 1997 but decreased in 1998. While increasing plant density reduced absolute fitness, presumably as a result of increased competition, a genetic polymorphism was not more likely to be maintained at low than high density as we had predicted. Within each density, the impact of disease was insufficient to reverse the slope of the relationship between absolute fitness and planted Frequency from positive to negative for the less competitive host genotype, thus preventing the maintenance of a genetic polymorphism.

  • DISEASE, Frequency-Dependent Selection, AND GENETIC POLYMORPHISMS: EXPERIMENTS WITH STRIPE RUST AND WHEAT
    Evolution; international journal of organic evolution, 2000
    Co-Authors: Johanne Brunet, Christopher C. Mundt
    Abstract:

    Pathogens have the potential to maintain genetic polymorphisms by creating Frequency-Dependent Selection on their host. This can occur when a rare host genotype is less likely to be attacked by a pathogen (Frequency-Dependent disease attack) and has higher fitness at low Frequency (negative Frequency-Dependent Selection). In this study, we used wheat genotypes that were susceptible to different races of the pathogen Puccinia striiformis to test whether disease created Frequency-Selection on its host and whether such Selection could maintain polymorphisms for resistance genes in the wheat populations. Four different two-way mixtures of wheat genotypes were planted at different fre- quencies in both the presence and absence of disease. Disease created Frequency-Dependent Selection on its host in some populations. Unknown factors other than disease also created Frequency-Dependent Selection in this system because, in some instances, rare genotype advantage was observed in the absence of disease. Although the pathogen created Frequency-Dependent Selection on its host, this Selection was not sufficient to maintain genetic polymorphism in the host populations. In all cases where Frequency-Dependent Selection occurred only in the diseased plots, one of the two genotypes was predicted to dominate in the population and the same genotype was predicted to dominate in both the presence and absence of disease. Only in cases where Frequency-Dependent Selection was not caused by disease was there evidence that genetic polymorphisms would be maintained in the population. The Frequency- Dependent Selection described in this study is a consequence of epidemiological effects of disease and differs from the time-lagged Frequency-Dependent Selection resulting from coevolution between hosts and parasites. The impact of this direct Frequency-Dependent Selection on the maintenance of genetic polymorphisms in the host population is discussed.

Shin-ichi Akimoto - One of the best experts on this subject based on the ideXlab platform.

  • Frequency-Dependent Selection acting on the widely fluctuating sex ratio of the aphid Prociphilus oriens.
    Journal of evolutionary biology, 2017
    Co-Authors: Shin-ichi Akimoto
    Abstract:

    Frequency-Dependent Selection is a fundamental principle of adaptive sex-ratio evolution in all sex ratio theories but has rarely been detected in the wild. Through long-term censuses, we confirmed large fluctuations in the population sex ratio of the aphid Prociphilus oriens and detected Frequency-Dependent Selection acting on these fluctuations. Fluctuations in the population sex ratio were partly attributable to climatic factors during the growing season. Climatic factors likely affected the growth conditions of host plants, which in turn led to yearly fluctuations in maternal conditions and sex ratios. In the process of Frequency-Dependent Selection, female proportion higher or lower than ca. 60% was associated with a reduction or increase in female proportion, respectively, the next year. The rearing of aphid clones in the laboratory indicated that mothers of each clone produced an increasing number of females as maternal size increased. However, the mean male number was not related to maternal size, but varied largely among clones. Given genetic variance in the ability to produce males among clones, Selection should favor clones that can produce more numerous males in years with a high female proportion. Population-level sex allocation to females was on average 71%–73% for three localities and more female-biased when maternal conditions were better. This tendency was accounted for by the hypothesis of competition among foundresses rather than the hypothesis of local mate competition. We conclude that despite consistent operation of Frequency-Dependent Selection, the sex ratio continues to fluctuate because environmental conditions always push it away from equilibrium. This article is protected by copyright. All rights reserved.