Fish reveal survival strategy: speed of life trades reproduction for disease resistance
Trinidadian guppies living in fast-paced environments sacrifice reproductive capacity to tolerate parasites, while slower-living populations invest in blocking infection. The finding suggests that evolutionary pressures shape disease tolerance differently across populations—a pattern with implications for understanding how species adapt to climate change and emerging pathogens.
Originaltitel: Pace of life predicts parasite resistance and fecundity tolerance, but not mortality tolerance, among Trinidadian guppies, Poecilia reticulata
<p>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. How hosts defend themselves against parasites can increase or decrease the size of the parasite population, and thus future infection risk. This epidemiological feedback may therefore shape host investment across elements of defense, which include limiting parasite growth ("resistance"), and limiting the reproductive and mortality costs of infection ("fecundity" and "mortality tolerance", respectively). In parallel, investment in these defenses should be dictated by host life history. These ideas are well-established theoretically, and our results suggest that they shape guppy, Poecilia reticulata, investment in defense against Gyrodactylus turnbulli. Guppy populations with faster paces of life invested less in resistance and fecundity tolerance than those with slower paces of life, in line with life-history theory. However, the populations did not differ in mortality tolerance, conforming to theoretical predictions: variation in mortality tolerance should be low, as longer-lived hosts transmit parasites for longer, creating positive frequency-dependent selection for this defense strategy.</p>