Ecological immunology and tolerance in plants and animals

P>1. Most animal studies of ecological immunology have focused on parasite resistance: defence mechanisms through which animals prevent infection or reduce parasite growth. Resistance mechanisms have obvious fitness benefits by reducing the fitness losses attributed to infection. 2. Intriguingly, animal researchers have largely ignored the role of tolerance mechanisms, through which hosts do not reduce parasite infection or growth, but alleviate the negative fitness consequences of parasite infection or growth instead. This omission stands in sharp contrast with the plant literature, where tolerance has been studied for decades and led to many important insights. 3. Here, we show that the plant literature has a lot to offer for understanding defence against parasites in animals. We argue that the prevailing views on tolerance in the plant literature should direct research on animals, and that theoretical ecological and evolutionary studies should be built on tolerance measures that are feasible and relevant in empirical studies. 4. Studying tolerance will enhance our understanding of how animals deal with parasites in their natural environments and may provide novel ways to combat disease.