Running with the Red Queen: host-parasite coevolution selects for biparental sex - PubMed (original) (raw)

Running with the Red Queen: host-parasite coevolution selects for biparental sex

Levi T Morran et al. Science. 2011.

Abstract

Most organisms reproduce through outcrossing, even though it comes with substantial costs. The Red Queen hypothesis proposes that selection from coevolving pathogens facilitates the persistence of outcrossing despite these costs. We used experimental coevolution to test the Red Queen hypothesis and found that coevolution with a bacterial pathogen (Serratia marcescens) resulted in significantly more outcrossing in mixed mating experimental populations of the nematode Caenorhabditis elegans. Furthermore, we found that coevolution with the pathogen rapidly drove obligately selfing populations to extinction, whereas outcrossing populations persisted through reciprocal coevolution. Thus, consistent with the Red Queen hypothesis, coevolving pathogens can select for biparental sex.

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Figures

Fig. 1

Fig. 1

Wildtype outcrossing rates over time. Outcrossing rates in wildtype populations were not manipulated and free to evolve during the experiment. The wildtype populations were exposed to three different treatments: control (no S. marcescens; dotted line), evolution (fixed strain of S. marcescens; dashed line), and coevolution (coevolving S. marcescens; solid line) for thirty generations. Error bars represent two standard errors of the mean (SE).

Fig. 2

Fig. 2

Coevolutionary dynamics of hosts and pathogens. We exposed hosts evolved under the coevolution treatment and their ancestral populations (prior to coevolution) to three pathogen populations: an ancestor strain (ancestral to all S. marcescens used in this study), a non-coevolving strain (evolved without selection), and their respective coevolving strain (coevolving with the host population). We evaluated host mortality after twenty-four hours of exposure to the pathogens and present the means across the replicate host populations. A. Three obligately selfing C. elegans populations persisted beyond ten host generations in the coevolution treatment. These populations were assayed prior to extinction. B. All five wildtype C. elegans populations in the coevolution treatment and their ancestors were assayed at the endpoint of the experiment (thirty host generations). C. All five obligately outcrossing C. elegans populations in the coevolution treatment and their ancestors were assayed at the endpoint of the experiment. Error bars represent two standard errors of the mean (SE).

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