Variation in resource acquisition and use among host clones creates key epidemiological trade‐offs

Parasites can certainly harm host fitness. Given such virulence, hosts should evolve strategies to resist or tolerate infection. But what governs those strategies and the costs that they incur? This study illustrates how a fecundity‐susceptibility trade‐off among clonally reared genotypes of a zooplankton (Daphnia dentifera) infected by a fungal parasite (Metschnikowia) arises due to variation in resource acquisition and use by hosts. To make these connections, we used lab experiments and theoretical models that link feeding with susceptibility, energetics, and fecundity of hosts. These feeding‐based mechanisms also produced a fecundity‐survivorship trade‐off. Meanwhile, a parasite spore yield–fecundity trade‐off arose from variation in juvenile growth rate among host clones (another index of resource use), a result that was readily anticipated and explained by the models. Thus, several key epidemiological trade‐offs stem from variation in resource acquisition and use among clones. This connection should catalyze the creation of new theory that integrates resource‐ and gene‐based responses of hosts to disease.