A mathematical model for interaction of gene frequencies in a parasite and its host.
TL;DR: Model for interaction of gene frequencies between a parasite and its host has been treated and it has been shown that in certain situations, one of the species may remain dimorphic while the other becomes monomorphic.
About: This article is published in Theoretical Population Biology.The article was published on 1970-08-01. It has received 114 citations till now.
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TL;DR: This analysis supports a ‘trench warfare’ hypothesis, in which advances and retreats of resistance-allele frequency maintain variation for disease resistance as a dynamic polymorphism, in the context of the short-term ecological dynamics of disease resistance.
Abstract: The co-evolutionary 'arms race' is a widely accepted model for the evolution of host-pathogen interactions. This model predicts that variation for disease resistance will be transient, and that host populations generally will be monomorphic at disease-resistance (R-gene) loci. However, plant populations show considerable polymorphism at R-gene loci involved in pathogen recognition. Here we have tested the arms-race model in Arabidopsis thaliana by analysing sequences flanking Rpm1, a gene conferring the ability to recognize Pseudomonas pathogens carrying AvrRpm1 or AvrB. We reject the arms-race hypothesis: resistance and susceptibility alleles at this locus have co-existed for millions of years. To account for the age of alleles and the relative levels of polymorphism within allelic classes, we use coalescence theory to model the long-term accumulation of nucleotide polymorphism in the context of the short-term ecological dynamics of disease resistance. This analysis supports a 'trench warfare' hypothesis, in which advances and retreats of resistance-allele frequency maintain variation for disease resistance as a dynamic polymorphism.
593 citations
TL;DR: A range of factors is considered that may influence the significance of genetic diversity for the survival of a population and the possibilities for application of current knowledge on genetic diversity and population survival for the management of natural populations are discussed.
Abstract: In this comprehensive review, a range of factors is considered that may influence the significance of genetic diversity for the survival of a population. Genetic variation is essential for the adaptability of a population in which quantitatively inherited, fitness-related traits are crucial. Therefore, the relationship between genetic diversity and fitness should be studied in order to make predictions on the importance of genetic diversity for a specific population. The level of genetic diversity found in a population highly depends on the mating system, the evolutionary history of a species and the population history (the latter is usually unknown), and on the level of environmental heterogeneity. An accurate estimation of fitness remains complex, despite the availability of a range of direct and indirect fitness parameters. There is no general relationship between genetic diversity and various fitness components. However, if a lower level of heterozygosity represents an increased level of inbreeding, a reduction in fitness can be expected. Molecular markers can be used to study adaptability or fitness, provided that they represent a quantitative trait locus (QTL) or are themselves functional genes involved in these processes. Next to a genetic response of a population to environmental change, phenotypic plasticity in a genotype can affect fitness. The relative importance of plasticity to genetic diversity depends on the species and population under study and on the environmental conditions. The possibilities for application of current knowledge on genetic diversity and population survival for the management of natural populations are discussed.
359 citations
TL;DR: Although assuming an empirically common type of asymmetrical gene–for–gene interaction, both host and parasite populations can maintain polymorphism in each locus and retain complex fluctuations.
Abstract: This paper examines a mathematical model for the coevolution of parasite virulence and host resistance under a multilocus gene-for-gene interaction. The degrees of parasite virulence and host resistance show coevolutionary cycles for sufficiently small costs of virulence and resistance. Besides these coevolutionary cycles of a longer period, multilocus genotype frequencies show complex fluctuations over shorter periods. All multilocus genotypes are maintained within host and parasite classes having the same number of resistant/virulent alleles and their frequencies fluctuate with approximately equally displaced phases. If either the cost of virulence or the number of resistance loci is larger then a threshold, the host maintains the static polymorphism of singly (or doubly or more, depending on the cost of resistance) resistant genotypes and the parasite remains universally avirulent. In other words, host polymorphism can prevent the invasion of any virulent strain in the parasite. Thus, although assuming an empirically common type of asymmetrical gene-for-gene interaction, both host and parasite populations can maintain polymorphism in each locus and retain complex fluctuations. Implications for the red queen hypothesis of the evolution of sex and the control of multiple drug resistance are discussed.
244 citations
Cites background from "A mathematical model for interactio..."
...The simplest model of gene-for-gene interactions assumes haploid, single-locus inheritance in host resistance and parasite virulence (e.g. Jayakar 1970) (see Seger & Hamilton (1988) for the matching genotype versions)....
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...The most important contribution of this model to the theory of host^parasite coevolution and the red queen hypothesis for the evolution of sex ( Jayaker 1970; Jeanike 1978; Bremermann 1980; Hamilton 1980; Seger & Hamilton 1988; Hamilton et al. 1990; Frank 1993) is that both genetic diversity in host and parasite genotypes and the complex cycles of their frequencies are promoted under the asymmetrical gene-for-gene system often found in ......
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TL;DR: The host snail and its trematode parasite seem to be dispersing to adjacent lakes in a stepping‐stone fashion, although parasite dispersal among lakes is clearly greater, which should help to continuously reintroduce genetic diversity within local populations where strong selection might otherwise isolate “host races.”
Abstract: Gene flow and the genetic structure of host and parasite populations are critical to the coevolutionary process, including the conditions under which antagonistic coevolution favors sexual reproduction. Here we compare the genetic structures of different populations of a freshwater New Zealand snail (Potamopyrgus antipodarum) with its trematode parasite (Microphallus sp.) using allozyme frequency data. Allozyme variation among snail populations was found to be highly structured among lakes; but for the parasite there was little allozyme structure among lake populations, suggesting much higher levels of parasite gene flow. The overall pattern of variation was confirmed with principal component analysis, which also showed that the organization of genetic differentiation for the snail (but not the parasite) was strongly related to the geographic arrangement of lakes. Some snail populations from different sides of the Alps near mountain passes were more similar to each other than to other snail populations on the same side of the Alps. Furthermore, genetic distances among parasite populations were correlated with the genetic distances among host populations, and genetic distances among both host and parasite populations were correlated with "stepping-stone" distances among lakes. Hence, the host snail and its trematode parasite seem to be dispersing to adjacent lakes in a stepping-stone fashion, although parasite dispersal among lakes is clearly greater. High parasite gene flow should help to continuously reintroduce genetic diversity within local populations where strong selection might otherwise isolate "host races." Parasite gene flow can thereby facilitate the coevolutionary (Red Queen) dynamics that confer an advantage to sexual reproduction by restoring lost genetic variation.
224 citations
TL;DR: A conclusion of whether the RQH can explain the maintenance of sexual reproduction cannot be reached at present, but it has shed light on many aspects of plant/pathogen interactions important for reducing pathogen damage in agricultural systems.
Abstract: The Red Queen Hypothesis (RQH) explains how pathogens may maintain sexual reproduction in hosts. It assumes that parasites become specialized on common host genotypes, reducing their fitness. Such frequency-dependent selection favors sexual reproduction in host populations. Necessary conditions are that resistance and virulence are genotype specific so that host genotype frequencies respond to changes in pathogen genotype frequencies, and vice versa. Empirical evidence on the genetic basis of disease, variation in resistance and virulence, and patterns of infection in sexual and asexual plants support certain features of the hypothesis. However, gene-for-gene interactions are generally not consistent with the RQH because they do not result in cycling of gene frequencies, unlike a matching allele mechanism. A conclusion of whether the RQH can explain the maintenance of sexual reproduction cannot be reached at present. Nevertheless, the RQH theory has shed light on many aspects of plant/pathogen interactions important for reducing pathogen damage in agricultural systems.
201 citations
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TL;DR: The genetic systems uncovered by the work of Flor, Briggs, and his associates will be briefly reviewed and their evolutionary significance will be interpreted from the standpoint of population genetics.
Abstract: The genetics of disease resistance in plants has been studied by numerous investigators since Biffen first reported in 1905 that host resistance to plant pathogens was a Mendelian character. Although a considerable literature on the . genetics of disease resistance has accumulated through the years, the work of Flor, Briggs, and his associates is particularly notable in that a concerted effort has been made to explore the genetic structure of a species in terms of disease resistance. In the present paper, the genetic systems uncovered by the work of Flor, Briggs, and his associates will be briefly reviewed and their evolutionary significance will be interpreted from the standpoint of population genetics.
150 citations