title: Host-parasite coevolution favours parasite genetic diversity and horizontal gene transfer.
abstract: Host-parasite coevolution is predicted to favour genetic diversity and the underlying mechanisms (e.g. sexual reproduction and, more generally, genetic exchange), because diversity enhances the antagonists' potential for rapid adaptation. To date, this prediction has mainly been tested and confirmed for the host. It should similarly apply to the parasite. Indeed, our previous work demonstrated that experimental coevolution between the nematode Caenorhabditis elegans and its microparasite Bacillus thuringiensis selects for genetic diversity in both antagonists. For the parasite, the previous analysis was based on plasmid-encoded toxin gene markers. Thus, it was restricted to a very small part of the bacterial genome and did not cover the main chromosome, which harbours a large variety of virulence factors. Here, we present new data for chromosomal gene markers of B. thuringiensis and combine this information with the previous results on plasmid-encoded toxins. Our new results demonstrate that, in comparison with the control treatment, coevolution with a host similarly leads to higher levels of genetic diversity in the bacterial chromosome, thus indicating the relevance of chromosomal genes for coevolution. Furthermore, the frequency of toxin gene gain is significantly elevated during coevolution, highlighting the importance of horizontal gene transfer as a diversity-generating mechanism. In conclusion, our study emphasizes the strong influence of antagonistic coevolution on parasite genetic diversity and gene exchange.
authors.affiliation: Institute for Evolution and Biodiversity, University of Muenster, Muenster, Germany. rebecca.schulte@biologie.uni-osnabrueck.de
authors.forename: R D
authors.initials: RD
authors.lastname: Schulte
authors.forename: C
authors.initials: C
authors.lastname: Makus
authors.forename: H
authors.initials: H
authors.lastname: Schulenburg
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics*; D005075:Biological Evolution; D017173:Caenorhabditis elegans / Q000235:genetics / Q000382:microbiology*; D002876:Chromosomes, Bacterial / Q000235:genetics; D022761:Gene Transfer, Horizontal; D014644:Genetic Variation; D005838:Genotype; D006790:Host-Parasite Interactions / Q000235:genetics
keywords: Bacillus thuringiensis; Caenorhabditis elegans; Red Queen; genetic diversity; horizontal gene transfer; host-parasite coevolution