The relative importance of host characteristics and co-infection in generating variation inHeligmosomoides polygyrusfecundity

Abstract

SUMMARYWe examined the relative importance of intrinsic host factors and microparasite co-infection in generating variation inHeligmosomoides polygyrusfecundity, a parameter that serves as a proxy for infectiousness. We undertook extensive trapping ofApodemus flavicollis, the yellow-necked mouse in the woodlands of the Italian Alps and recorded eggsin uterofrom the dominant nematode speciesH. polygyrus, and tested for the presence of five microparasite infections. The results showed that sex and breeding status interact, such that males in breeding condition harboured more fecund nematodes than other hosts; in particular, worms from breeding males had, on average, 52% more eggsin uterothan worms from non-breeding males. In contrast, we found a weak relationship between intensity and body mass, and no relationship between intensity and sex or intensity and breeding condition. We did not find any evidence to support the hypothesis that co-infection with microparasites contributed to variation in worm fecundity in this system. The age-intensity profiles for mice singly-infected withH. polygyrusand those co-infected with the nematode and at least one microparasite were both convex and not statistically different from each other. We concluded that intrinsic differences between hosts, specifically with regard to sex and breeding condition, contribute relatively more to the variation in worm fecundity than parasite co-infection status.