The evolution of host defence when parasites impact reproduction

Question: How does the evolution of host defences to parasitism depend on the level of disease-induced sterility?

Mathematical Methods: Evolutionary invasion analysis (adaptive dynamics) applied to susceptible-infected host-parasite model.

Key assumptions: Hosts can evolve defence through avoidance (lower transmission), clear- ance (higher recovery) or tolerance (lower virulence), in isolation or simultaneously, at a cost to their reproductive rate. Separation of ecological and evolutionary timescales and mutations of small phenotypic effect.

Conclusions: Avoidance and clearance are maximised when sterility is high, but tolerance is greatest when sterility is low. However when clearance and tolerance co-evolve there is greater tolerance at high sterility as this boosts the effectiveness of clearance. Patterns of investment along other environmental gradients can change as the level of sterility changes. Evolutionary branching to coexistence in avoidance and clearance is most likely when sterility is high.