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Incorporating ecology into virulence evolution: an experimental evolution approach

Supervisors: Dr Helen Leggett [co-supervisor Dr Howard Baylis]

Project summary:

The aim of this project is to use a powerful experimental evolution system comprising bacterial pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) infecting Caenorhabditis elegans nematodes, to address 3 key unanswered questions: 1) How do parasite interactions within- and between- hosts affect virulence-transmission trade-offs, and what are the associated genomic changes? 2) Are virulent parasites competitively superior and do they obtain greater transmission from mixed infections than less virulent parasites? 3) How does host and multi-parasite coevolution affect virulence evolution? By introducing multiple parasite species into a host–parasite co-evolutionary framework where infections occur naturally, this project will provide useful insights as to how evolution operates in host-parasite interactions in nature.

In an increasingly “post antibiotic era”, creative approaches to combatting infections are paramount. Identifying common factors in the evolution of parasite life histories and virulence would give us predictive power, and thus the opportunity to develop management strategies with broad applicability. Key to understanding virulence is understanding how parasites deal with competition from other parasites within hosts, and optimise their transmission between hosts. Parasites need to transmit to survive, and they buy transmission at the expense of damaging their host as they grow inside them: if they grow too much, they kill their host before they can transmit; but if they don’t grow enough, they are out-competed by faster growing parasites. And its not just other parasites the parasites have to compete with: hosts evolve resistance, leading to a host-parasite arms-race. However, these critical interactions have not been rigorously tested due to a lack of experimental systems. This project tackles this using a powerful system of worms infected with bacteria, where the infection process is natural and we can study evolution in real time.

What the student will be doing:

• perform three long-term selection experiments, one for each of the questions above. This will involve learning techniques in nematode and bacterial culturing, designing and executing carefully controlled evolution experiments in the lab, and using phenotypic assays and genetic tools to analyse associated changes at the phenotype and genome levels. • Have the opportunity to take a complimentary comparative approach (meta-analysis) to elucidate broad patterns across different parasite species using a database I have developed, to gain rigorous literature review and meta-analysis skills. • Have the opportunity to attend EMPSEB, the largest international graduate student conference in this field, to gain conference experience and to network.

References:

Leggett H.C., Buckling A., Long G. & Boots M. 2013. Generalism and the evolution of parasite virulence. Trends in Ecology and Evolution, 28(10) 592-596. doi:10.1016/j.tree.2013.07.002
 
Frank, S.A. 1996. Models of Parasite Virulence. The Quarterly Review of Biology, Vol. 71, No. 1, pp. 37-78
 
Alizon S, de Roode JC, Michalakis Y. 2013. Multiple infections and the evolution of virulence. Ecology Letters, 16(4):556-67. doi: 10.1111/ele.12076. Epub 2013 Jan 24.