Evidence for Maintenance of Sex by Pathogens in Plants

Abstract

Abstract. The predominance of outcrossing despite the substantial transmission advantage of self-fertilization remains a paradox. Theory suggests that selection can favor outcrossing if it enables the production of offspring that are less susceptible to pathogen attack than offspring produced via self-fertilization. Thus, if pathogen pressure is contributing to the maintenance of outcrossing in plants, there may be a positive correlation between the number of pathogen species attacking plant species and the outcrossing rate of the plant species. We tested this hypothesis by examining the association between outcrossing rate and the number of fungal pathogen species that attack a large, taxonomically diverse set of seed plants. We show that plant species attacked by more fungal pathogen species have higher outcrossing rates than plants with fewer enemies. This relationship persists after correcting for study bias among natural and agricultural species of plants. We also accounted for the nested hierarchy of relationships among plant lineages by conducting phylogenetically independent contrasts (PICs) within genera and families that were adequately represented in our dataset. A meta-analysis of the correlation between pathogen and outcrossing PICs shows that there is a positive correlation between pathogen species number and outcrossing rates. This pattern is consistent with the hypothesis that pathogen-mediated selection may contribute to the maintenance of outcrossing in species of seed plants.

An epidemiological model of host–parasite coevolution and sex

“…The basic tenets of this idea (the 'parasite' or 'Red Queen' hypothesis for sex) have received recent empirical support from a variety of different sources (e.g. Busch et al, 2004;Decaestecker et al, 2007;Jokela et al, 2009;King et al, 2009;Koskella & Lively, 2009;Wolinska & Spaak, 2009;Paterson et al, 2010).…”

Parasite virulence, host life history, and the costs and benefits of sex

“…One idea that has withstood empirical scrutiny, at least in some systems, is the Red Queen Hypothesis (Lively 1987, Busch et al 2004, Decaestecker et al 2007, King et al 2009, Wolinska and Spaak 2009. The gist of the Red Queen Hypothesis is that parasites should select against common genotypes, giving an advantage to the production of genetically variable offspring (Jaenike 1978, Hamilton 1980, Lloyd 1980, Hamilton et al 1990).…”

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

“…There is a positive correlation between the number of fungal pathogen species known to infect a plant host and the outcrossing rate of the host (Busch et al 2004). In addition, species with higher outcrossing rates tend to occur in less disturbed, biologically complex habitats, where disease and other 'natural enemies' are likely to be more prevalent (see Levin (1975), although alternative explanations for this pattern exist).…”