Pace of life predicts parasite resistance and fecundity tolerance, but not mortality tolerance, among Trinidadian guppies, <i>Poecilia reticulata</i>

Abstract Host defense against parasites can include limiting parasite growth, “resistance,” limiting the mortality cost of infection, “mortality tolerance,” and limiting the reproductive cost of infection, “fecundity tolerance.” Theoretically, these 3 host strategies have very different epidemiological and evolutionary outcomes. In particular, because mortality tolerance increases parasite population size, it is under strong positive frequency-dependent selection and may therefore be less variable between populations than either resistance or fecundity tolerance. Additionally, host investment in each strategy can be expected to differ between populations that experience different ecological conditions. Here, we tested how populations of Trinidadian guppies Poecilia reticulata from the upper and lower courses of 3 rivers responded to experimental infection with a novel strain of Gyrodactylus turnbulli. In line with theoretical predictions, we found that lower course populations, previously shown to have faster paces of life, invested less in resistance and fecundity tolerance—but not mortality tolerance—than the upper course populations with slower paces of life. Our results indicate that this host–parasite interaction both conforms to evolutionary-epidemiological theoretical predictions, and is shaped by broader ecological conditions.