Ecology and evolution of protective microbes

Thesis

Every host is colonized by a variety of microbes, some of which can protect their hosts from pathogen infection. Harbouring protective microbes (PMs) has evolutionary implications which often result in these microbes being costly for the host. Here I have investigated the evolutionary and ecological conditions under which the interaction between a host and a protective microbe are established. For this I have used populations of Caenorhabditis elegans worm hosts, bacteria possessing protective traits (Enterococcus faecalis) and pathogenic bacteria (Staphylococcus aureus). I have experimentally coevolved the host and protective microbe and infected the coevolving system at different intervals and host generations. Furthermore, I have investigated how host sex and mating status affects the interaction of the host with the surrounding bacteria. More generally, to assess how host dynamics are affected by protective microbes, I constructed SIR models in the absence and presence of the protective microbe. My results indicate that even the rare presence of the pathogen is enough to drive the evolution of microbe mediated protection, and that this is independent of the interval or initial pathogen presence. I find that both sexes use the benefits of the PM to increase their reproductive success, even though females invest more in egg production and males more in mate searching behaviour. The SIR models indicate that the protective microbe stabilises host dynamics under a range of different parameters once the cost-benefit ratio is greater than one. Overall these results suggest, that protective microbes have high potential to influence and stabilize host dynamics, even though the two host sexes might benefit differently from the provided protection.

Authors: Kloock, A

• DOI: 10.5287/ora-5zm1gebn0
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Experimental Evolution; Host-Pathogen Interactions; Protective microbes; Sexual Immune Dimorphism; Mathematical Modelling; Defensive Symbiosis
• Subjects: Evolution; Ecology; Mathematical models