Parasite Life History

For many parasites (e.g., malaria, trypanosomes), producing transmissible forms comes at the cost of producing fewer of the forms that are required for within-host survival. Thus, these parasites – like all sexually-reproducing organisms – face a resource allocation trade-off between growth (within-host survival) and reproduction (transmission).

Life history theory, largely developed to explain the biology of multicellular organisms, can also help us to understand the resolution of this tradeoff for malaria parasites and how it depends on within-host conditions. For example, parasites that share their host with other genotypes reduce their investment in transmission unless they are vastly outnumbered by competitors. These data appear to follow qualitative predictions from life history theory: reproductive restraint may improve survival in stressful conditions, but imminent death requires a terminal investment strategy. But definitively attributing this variation to adaptive plasticity in life history strategies is not easy. For instance, there is no evidence that decreasing investment in transmission when faced with a competitor results in higher fitness for parasites than if they had maintained their single-infection level of investment. This is because conducting experiments to investigate the fitness effects of making such alternative life-history decisions is currently not feasible.

Instead, we are developing mathematical theory to ask whether the observed patterns of investment in transmission are fitness-maximizing strategies for parasites and to predict optimal patterns of investment in different scenarios. Parasites are more complex and responsive critters than is often assumed; this research aims to illuminate that fact.

Relevant papers:

Mideo, N., Reece, S.E., Smith, A.L., & Metcalf, C.J.E. (2013) The Cinderella Syndrome: Why do malaria-infected cells burst at midnight? Trends in Parasitology, 29: 10-16. PDF

Carter, L.M., Kafsack, B.F.C., Llinás, M., Mideo, N., Pollitt, L.C., & Reece, S.E. Stress and sex in malaria parasites: why does commitment vary? Evolution, Medicine, and Public Health, 1: 135-147.

Brown, S.P., Cornforth, D., & Mideo, N. (2012) Evolution of virulence in opportunistic pathogens: generalism, plasticity, and control. Trends in Microbiology, 20: 336-342. PDF

Mideo N., & Reece S.E. (2012) Plasticity in parasite phenotypes: evolutionary and ecological implications for disease. Future Microbiology, 7: 17-24.PDF

Pollitt L.C., Mideo N., Drew D.R., Schneider P., Colegrave N., & Reece S.E. (2011) Competition and the evolution of reproductive restraint in malaria parasites. American Naturalist, 177: 358-367. PDF

Mideo N. (2009) Parasite adaptations to within-host competition. Trends in Parasitology 25: 261-268.PDF

Alizon S., Hurford A., Mideo N., & van Baalen M. (2009) Virulence evolution and the trade-off hypothesis: history, current state of affairs and future. Journal of Evolutionary Biology 22: 245-259.PDF

Mideo N., & Day T. (2008) On the evolution of reproductive restraint in malaria. Proceedings of the Royal Society, B 275: 1217-1224.  PDF APPENDICES Nature Research Highlight (Evolutionary biology)

Day T., Mideo N., & Alizon S. (2008) Why is HIV not insect-borne? Evolutionary Applications 1: 17-27. PDF