Pace of life predicts Trinidadian guppy parasite resistance and fecundity tolerance, but not mortality tolerance

Host defence 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 three host strategies have very different
epidemiological and evolutionary outcomes. In particular, because of its
positive effect on parasite population size, mortality tolerance should be
under strong positive 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 three 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.