Sex-dependent effects of infection on guppy reproductive fitness and offspring parasite resistance

O_LIInfection imposes energetic costs on hosts. Hosts typically respond by shifting resources, potentially affecting the quantity and quality of offspring they produce. As the sexes differ in their optimal reproductive strategies, infection of mothers versus fathers may affect offspring quantity and quality in different ways. C_LIO_LIHere, we test how experimental infection of guppies Poecilia reticulata with the ectoparasite Gyrodactylus turnbulli affects parental reproductive fitness and offspring parasite resistance. We compared breeding pairs in which one or neither parent had previously been infected. C_LIO_LIIn terms of reproductive fitness, parental infection experience did not affect the size, body condition, or number of offspring produced, but fathers who experienced the heaviest infections produced offspring [~]55 days sooner than average. This result may represent terminal investment by the males most affected by infection, or may indicate that these males have a faster pace of life, investing in reproduction at the expense of parasite defence. C_LIO_LIWe found that offspring age, parental infection experience, and parental infection severity together strongly predicted offspring parasite resistance. Only among pairs in which one parent had been infected, older offspring, which were those born soonest after the parents infection, tended to experience heavier infections. This result may therefore reflect temporary infection-induced reductions in parental investment in offspring quality. Beyond this effect of offspring age, offspring of infected mothers experienced 105 fewer worm days than those of infected fathers: fathers, but not mothers, that experienced heavy infections themselves produced offspring that also experienced heavy infections. The parent-offspring regression for infected fathers is therefore consistent with previous evidence that parasite resistance is heritable in this system, and yields a narrow sense heritability estimate of 0.69{+/-}0.13. By contrast, the mother-offspring regression (slope: -0.13{+/-}0.17) provides novel insight that mothers may engage in transgenerational immune priming. C_LIO_LIOverall, our results suggest that the sexes strike a different balance between offspring quantity and quality when faced with infection, with potentially broad implications for disease and host-parasite coevolutionary dynamics in nature. C_LI