Print PageParasites are thought to play an important role in the ecological and evolutionary dynamics of host populations, yet we still lack a mechanistic understanding of these effects. We studied parasite-mediated selection in seven lake populations of Daphnia dentifera, and asked whether the ecological context in which the host-parasite interaction is embedded influences the evolutionary dynamics. Specifically, we were interested in whether the predation and productivity environment of lakes influences the type of parasite-driven evolution that occurs and the severity of epidemics of the virulent yeast pathogen, Metschnikowia bicuspidata. To address this, we used a combination of 1) field monitoring of naturally occurring epidemics, 2) studies characterizing changes in the susceptibility of populations over the course of epidemics, and 3) mathematical models of this host-parasite interaction.
Results/Conclusions
We found that three D. dentifera populations became more resistant to Metschnikowia, while three became more susceptible during epidemics; the seventh population did not show a significant change in mean susceptibility. Our results can readily be explained by an observed trade-off between resistance and fecundity, as well as differences in ecological context. Specifically, we found that environments with low predation and high productivity had larger epidemics that selected for increased host resistance. Conversely, environments with high predation and low productivity had smaller epidemics and selection for increased susceptibility. Our results suggest that increases in disease susceptibility during epidemics may be common, and that the type of selection that occurs is strongly influenced by environmental context.
