The Costs and Benefits of Occasional Sex: Theoretical Predictions and a Case Study

D’Souza, Thomas G.; Michiels, Nico K.

doi:10.1093/jhered/esq005

Cited by 86 publications

(74 citation statements)

References 62 publications

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“…This problem can be circumvented by taking advantage of systems that feature both mating system and ploidylevel variation [47,48] and by comparing resistance in triploid and tetraploid asexuals.…”

Section: Direct Empirical Connectionsmentioning

confidence: 99%

Is more better? Polyploidy and parasite resistance

2012

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Ploidy-level variation is common and can drastically affect organismal fitness. We focus on the potential consequences of this variation for parasite resistance. First, we elucidate connections between ploidy variation and key factors determining resistance, including allelic diversity, gene expression and physiological condition. We then argue that systems featuring both natural and artificially manipulated ploidy variation should be used to evaluate whether ploidy level influences host -parasite interactions.Keywords: polyploidy; host-parasite interactions; allelic diversity; gene expression; host condition 1. INTRODUCTION Polyploidization 1 has generated variation in ploidy level within and across species [1,2], and new examples are continually being discovered, particularly in animals [3]. Intraspecific ploidy-level variation is associated with a suite of connections between polyploidy and biological phenomena [4,5], and has the potential to influence fitness-related traits [6,7]. We discuss whether ploidy variation could mediate resistance to a ubiquitous enemy-parasites (defined here as an organism that harms its host). Although current theory suggests ploidy level can profoundly influence infection dynamics and host-parasite evolution [8,9], data are scarce [10,11]. PLOIDY AND IMMUNE FUNCTIONPolyploidy (i.e. autopolyploidy) could directly influence immune response to a parasite attack in at least two ways. Firstly, the addition of a new genome may increase allelic diversity. Higher allelic diversity at immune genes could help hosts recognize a greater diversity of parasites [12]. Secondly, if the additional genome copies are expressed, then polyploids may generate higher amounts of gene products related to immune function.(a) Allelic diversity and immune function The high allelic diversity of immune genes is partly a consequence of parasite-mediated selection for rare genotypes and/or novel immune functions [13]. Parasitemediated selection may generate such diversity through mechanisms such as heterozygote advantage [14] and negative frequency-dependence [13]. Heterozygote advantage could be influenced by ploidy level because the extra alleles present in polyploids may increase the probability of heterozygosity for an individual at a given locus. The presence of an extra genome could also increase the likelihood that an individual possesses a rare genotype at resistance loci; this would be advantageous if parasite-mediated negative frequency-dependent selection favours rare genotypes.Studies from natural populations have documented connections between parasite-mediated selection and the maintenance of allelic variation at genes associated with immune function [12,15]. Genetic polymorphism can play an important role in generating variation in recognition molecules [16], and diversity is important for disease resistance in host individuals and populations [17,18]. Furthermore, measures of genome-wide genetic variation (e.g. microsatellite heterozygosity [19,20]) are often correlated with individual immune ...

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Section: Direct Empirical Connectionsmentioning

confidence: 99%

Is more better? Polyploidy and parasite resistance

2012

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“…Theoretically, facultative sex appears to be a superior solution to either asexuality or obligate sex: it offers much of the genetic advantages of sexual reproduction (e.g. increasing genetic diversity, avoidance of clonal interference, purging deleterious mutations) with a dramatic reduction of the frequency with which costs have to be paid [20], see also [21].…”

Section: Introductionmentioning

confidence: 99%

Sexual conflict and the evolution of asexuality at low population densities

Gerber

Kokko

2016

Proc. R. Soc. B.

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Theories for the evolution of sex rarely include facultatively sexual reproduction. Sexual harassment by males is an underappreciated factor: it should at first sight increase the relative advantage of asexual reproduction by increasing the cost of sex. However, if the same females can perform either sexual or asexual life cycles, then females trying to reproduce asexually may not escape harassment. If resisting male harassment is costly, it might be beneficial for a female to accept a mating and undertake a sexual life cycle rather than 'insist' on an asexual one. We investigate the effects of sexual harassment on the maintenance of sex under different population densities. Our model shows that resisting matings pays off at low population densities, which leads to the complete extinction of males, and thus to the evolution of completely asexual populations. Facultative sex persists in a narrow range of slightly higher densities. At high densities, selection favours giving up resisting male mating attempts and thus sexual reproduction takes over. These interactions between the outcomes of sexual conflict and population density suggest an explanation for the rarity of facultative sex and also patterns of geographical parthenogenesis, where marginal environments with potentially low densities are associated with asexuality.

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“…Consequently, it has been argued that rare males are nonfunctional and have no impact on the genetic diversity or evolution of parthenogenetic lineages (Lynch 1984;Palmer and Norton 1990;Bloszyk et al 2004). However, it has been reported in several cases that rare males are functional and may mate with sexual females of a closely related species (Simon et al 2003;D'Souza and Michiels 2010;Neiman et al 2012;Maccari et al 2013), and even transmit parthenogenesis to their offspring through a phenomenon called contagious parthenogenesis (Simon et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Rare diploid females coexist with rare males: a novel finding in triploid parthenogenetic populations in the psyllid Cacopsylla myrtilli (W. Wagner, 1947) (Hemiptera, Psylloidea) in northern Europe

2015

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Using a cytological approach, diploid females were found coexisting with rare males in triploid apomictic parthenogenetic populations of the psyllid Cacopsylla myrtilli (W. Wagner, 1947) in Norway, Sweden, Finland and northwest Russia. Diploid females were easily distinguished from triploid apomictic females by the presence of 13 chiasmate bivalents instead of 39 univalent chromosomes at metaphase I. Abundance equaled that of males, but the proportion of males and diploid females was significantly greater in high altitude compared with low altitude populations. Males mated with females but showed no mating preference for diploid females. Lack of genuine bisexual reproduction owing to either asynaptic meiosis in males, or rarity of males with normal meiosis, suggests that diploids are produced in every generation by parthenogenetic females as reversals from triploidy, with their production being enhanced by environmental factor(s) associated with high altitude. This is further supported by the observation that within a population the COI haplotype found in rare males was the same as that in parthenogenetic triploid females. Thus, in northern Europe parthenogenesis in C. myrtilli is obligate, geographic parthenogenesis. Bisexual populations of C. myrtilli should be looked for in Central and Southern Europe. From the evolutionary point of view, the presence of males and diploid females with normal meiosis in parthenogenetic populations could be significant as they exhibit the potential to re-evolve either a new sexual species of parthenogenetic ancestry or a new parthenogenetic species by contagious parthenogenesis.

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The Costs and Benefits of Occasional Sex: Theoretical Predictions and a Case Study

Cited by 86 publications

References 62 publications

Is more better? Polyploidy and parasite resistance

Is more better? Polyploidy and parasite resistance

Sexual conflict and the evolution of asexuality at low population densities

Rare diploid females coexist with rare males: a novel finding in triploid parthenogenetic populations in the psyllid Cacopsylla myrtilli (W. Wagner, 1947) (Hemiptera, Psylloidea) in northern Europe

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