Antagonistic coevolution between hosts and parasites is thought to maintain genetic diversity both within populations, as rare host genotypes are favored, and between populations, as parasite local adaptation drives host population divergence. Experimental evolution techniques allow for the direct examination of parasite-mediated selection on host populations and have proven invaluable in examining the process and implications of coevolution. A number of laboratory studies using bacteria and their parasitic phage have shown that antagonistic interactions play a key role in maintaining polymorphism over both space and time. It is critical, however, that results from experimental microcosm studies be interpreted in light of both ecological complexities and natural community dynamics.

Results/Conclusions

Using a combination of natural population surveys and controlled selection experiments, I have been investigating the impact of a hyperparasitic phage on the within and between-host diversity of a bacterial plant pathogen, Pseudomonas syringae. The results suggest that host environment plays a critical role in shaping the dynamics of hyperparasite adaptation and that bacterial community composition depends on the selective environment of both the host and the hyperparasite. These data suggest that understanding and predicting outcomes of antagonistic interactions can lend key insight into the maintenance of diversity.