Testing the role of spatial structure in ecology and evolution

Individuals tend to interact more with individuals that are close to them or in their social group. Similarly in diseases that are spread by contact, infected individuals are more likely to contact other individuals that are close by or in their social group. The disease therefore spreads spatially through the population. There has been a number of computer models that show that this spatial spread can have a major effect on the disease dynamics. Recent work has shown that this spatial structure can also have important implications to the evolution of parasites. If they spread locally, they are selected for lower transmission and virulence. It is very difficult to test this sort of theory, but we have developed an insect virus system in which we can manipulate how locally the hosts move. Our recent work using this system has confirmed the predictions of the model of the effect of space on transmission; it was lower in a more viscose population. We now want to examine the role of spatial structure on the coevolution of the host in addition to the parasite. As such we propose to build computer models and use some mathematical approximation techniques to predict the effect of local infection on host resistance. We will then test this using our insect virus system. This mixture of theory and ecological experimentation will give us a much clearer idea of the implications of different degrees of local interactions on the evolution of disease causing organisms. Given that anthropological changes are altering the mixing patterns within many populations, it is important that we understand what the implications are to wildlife and human disease.

"Our work emphasizes the importance of spatial structure to parasite evolution. This spatial evolutionary theory is important because it predicts how different pathogens may respond to changes in patterns of mixing.

We highlight the importance of landscape heterogeneity and the proximity and size of adjacent habitats when predicting disease risk in a particular location. In addition, our analysis could be useful for other pathogen systems with generalist vectors and may inform policy on possible disease management strategies that incorporate host movements.

Our work also emphasises that local processes are essential in determining parasite-driven extinctions, and the role of parasites in the extinction of rare species may have been underplayed due to the classic assumption of global density-dependent transmission."