The Maintenance of Sex by Parasitism and Mutation Accumulation Under Epistatic Fitness Functions

Howard, R. Stephen; Lively, Curtis M.

doi:10.1111/j.1558-5646.1998.tb01658.x

Cited by 82 publications

(89 citation statements)

References 30 publications

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“…Specifically, Howard and Lively (1994), and others since (Howard and Lively 1998;Park et al 2010), investigated the competitive ability of sexual vs. asexual populations of hosts in the presence of coevolving parasites and deleterious mutations. By focusing on the asexuals, we can compare their model with ours.…”

Section: Discussionmentioning

confidence: 99%

Temporal Variation in Selection Accelerates Mutational Decay by Muller’s Ratchet

Wardlaw

Agrawal

2012

Genetics

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Asexual species accumulate deleterious mutations through an irreversible process known as Muller's ratchet. Attempts to quantify the rate of the ratchet have ignored the role of temporal environmental heterogeneity even though it is common in nature and has the potential to affect overall ratchet rate. Here we examine Muller's ratchet in the context of conditional neutrality (i.e., mutations that are deleterious in some environmental conditions but neutral in others) as well as more subtle changes in the strength (but not sign) of selection. We find that temporal variation increases the rate of the ratchet (mutation accumulation) and the rate of fitness decline over that of populations experiencing constant selection of equivalent average strength. Temporal autocorrelation magnifies the effects of temporal heterogeneity and can allow the ratchet to operate at large population sizes in which it would be halted under constant selection. Classic studies of Muller's ratchet show that the rate of fitness decline is maximized when selection is of a low but intermediate strength. This relationship changes quantitatively with all forms of temporal heterogeneity studied and changes qualitatively when there is temporal autocorrelation in selection. In particular, the rate of fitness decline can increase indefinitely with the strength of selection with some forms of temporal heterogeneity. Our finding that temporal autocorrelation in selection dramatically increases ratchet rate and rate of fitness decline may help to explain the paucity of asexual taxa.

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Section: Discussionmentioning

confidence: 99%

Temporal Variation in Selection Accelerates Mutational Decay by Muller’s Ratchet

Wardlaw

Agrawal

2012

Genetics

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“…Even though the rate of mutation per genome has not been studied in psychid moths, most asexual populations are quite small (see Materials and Methods) and hence the conditions could also be suitable for Muller's ratchet (Muller 1964) to work. However, West et al (1999) emphasized the importance of a pluralistic view instead of finding simple explanations for the maintenance of sex in complex systems, and Howard and Lively (1998) suggested that even moderate effects of parasites together with mutation accumulation could act in favor of sex. However, in our study system it is unlikely that mutation accumulation could explain the maintenance of sexuals as the life-history measurements do not indicate any phenotypic abnormalities among the asexuals.…”

Section: Discussionmentioning

confidence: 99%

“…Theoretical studies have often focused on the success of sexuals versus asexuals (e.g., Rispe and Pierre 1998;Doncaster et al 2000;Peck and Waxman 2000), but the actual paradox of the maintenance of sex still remains. Apart from the outstanding studies on New Zealand freshwater snails (Lively 1992;Fox et al 1996;Jokela et al 1997;Howard and Lively 1998), there is very little empirical data from natural systems where sexually and asexually reproducing morphs of nonhybrid origin coexist and compete with each other (snail, Campeloma limum: Johnson 2000; flatworm, Schmidtea polychroa: Michiels et al 2001).…”

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Parasites and Sexual Reproduction in Psychid Moths

2004

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Abstract. Persistence of sexual reproduction among coexisting asexual competitors has been a major paradox in evolutionary biology. The number of empirical studies is still very limited, as few systems with coexisting sexual and strictly asexual lineages have been found. We studied the ecological mechanisms behind the simultaneous coexistence of a sexually and an asexually reproducing closely related species of psychid moth in Central Finland between 1999 and 2001. The two species compete for the same resources and are often infected by the same hymenopteran parasitoids. They are extremely morphologically and behaviorally similar and can be separated only by their reproductive strategy (sexual vs. asexual) or by genetic markers. We compared the life-history traits of these species in two locations where they coexist to test predictions of the cost-of-sex hypothesis. We did not find any difference in female size, number of larvae, or offspring survival between the sexuals and asexuals, indicating that sexuals are subject to cost of sex. We also used genetic markers to check and exclude the possibility of Wolbachia bacteria infection inducing parthenogenesis. None of the samples was infected by Wolbachia and, thus, it is unlikely that these bacteria could affect our results. We sampled 38 locations to study the prevalence of parasitoids and the moths' reproductive strategy. We found a strong positive correlation between prevalence of sexual reproduction and prevalence of parasitoids. In locations where parasitoids are rare asexuals exist in high densities, whereas in locations with a high parasitoid load the sexual species was dominant. Spatial distribution alone does not explain the results. We suggest that the parasite hypothesis for sex may offer an explanation for the persistence of sexual moths in this system. Key words. Bag worm moth, cost of sex, parasite hypothesis, parthenogenesis, Red Queen hypothesis, Wolbachia.Received October 8, 2003. Accepted February 9, 2004 Maintenance of sexual reproduction has been a puzzling question in the theory of evolution since it was first raised by Williams (1975), Maynard Smith (1978), and Bell (1982. Many hypotheses have been presented to explain the maintenance of sex (e.g., Kondrashov 1993;Hurst and Peck 1996;Lively 1996; Jokela et al. 2003), since the asexually reproducing morphs could produce offspring more effectively than the sexuals by avoiding the costs of producing males. This cost of sex should finally lead to replacement of sexuals if the all-else-equal assumption is true (Maynard Smith 1978). In the long term, this should lead to natural populations consisting purely of asexually reproducing females, unless there are some short-term advantages of sexual reproduction (e.g., Lively 1996). Such short-term advantages could arise from the genetic recombination in cross-fertilization, which purges deleterious mutations and increases the amount of genetic variation (Muller 1964;Kondrashov 1988;Rice 2002).The importance of variation in the host genotype was further ...

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“…Jaenike 1977;Hamilton 1980;Hamilton et al 1990;Howard & Lively 1998). Two previous studies have contrasted selffertilization ('selfing') and outcrossing, both of which are forms of sexual reproduction.…”

Section: Introductionmentioning

confidence: 99%

Host mating system and the prevalence of disease in a plant population

Koslow

Jiang

2006

Proc. R. Soc. B.

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A modified susceptible-infected-recovered (SIR) host-pathogen model is used to determine the influence of plant mating system on the outcome of a host-pathogen interaction. Unlike previous models describing how interactions between mating system and pathogen infection affect individual fitness, this model considers the potential consequences of varying mating systems on the prevalence of resistance alleles and disease within the population. If a single allele for disease resistance is sufficient to confer complete resistance in an individual and if both homozygote and heterozygote resistant individuals have the same mean birth and death rates, then, for any parameter set, the selfing rate does not affect the proportions of resistant, susceptible or infected individuals at equilibrium. If homozygote and heterozygote individual birth rates differ, however, the mating system can make a difference in these proportions. In that case, depending on other parameters, increased selfing can either increase or decrease the rate of infection in the population. Results from this model also predict higher frequencies of resistance alleles in predominantly selfing compared to predominantly outcrossing populations for most model conditions. In populations that have higher selfing rates, the resistance alleles are concentrated in homozygotes, whereas in more outcrossing populations, there are more resistant heterozygotes.

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The Maintenance of Sex by Parasitism and Mutation Accumulation Under Epistatic Fitness Functions

Cited by 82 publications

References 30 publications

Temporal Variation in Selection Accelerates Mutational Decay by Muller’s Ratchet

Temporal Variation in Selection Accelerates Mutational Decay by Muller’s Ratchet

Parasites and Sexual Reproduction in Psychid Moths

Host mating system and the prevalence of disease in a plant population

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