When battling an epidemic of a deadly parasite, less resistance can sometimes be better than more. A new study suggests that a lake’s ecological characteristics influence how freshwater zooplankton Daphnia dentifera evolve to survive epidemics of a virulent yeast parasite Metschnikowia bicuspidate. The study found that Daphnia populations evolved either enhanced resistance or susceptibility to infection depending on the nutrient concentration and predation levels in the lake.