1. Macroparasites have a central place in wildlife ecology because they have the potential
to regulate host populations through effects on reproduction and/or survival.
However, there remains a paucity of studies that have demonstrated the
regulatory role of these parasites in free-ranging animals.
2. Previous work on Svalbard reindeer demonstrated that the experimental removal
of the parasitic gastrointestinal nematode Ostertagia gruehneri transmitted in summer,
improved reindeer fecundity, and that the species was capable of mediating a
density-dependent reduction in fecundity.
3. The main coexisting parasitic nematode in the system, Marshallagia marshalli, exhibits
a contrasting life history with low abundances in summer and an increase during
the winter. Here, we examine the impact of this over-winter infection on fitness of
female reindeer in the same population.
4. Worm burdens were removed at the start of the winter in October using a novel
delayed-release anthelmintic bolus. Body mass and pregnancy rates were recorded
for animals recaptured five (February) and seven (April) months later. The sub-set
of treated animals recaptured in February was treated again with anthelmintic to
remove newly acquired nematodes. The experiment was replicated over six winters
(2006/2007-2011/2012) with a total of 343 recaptures, comprising 145 individual
animals.
5. We found little effect of anthelmintic treatment on reindeer body mass or pregnancy
rates during the winter, suggesting that nematode infection during this time
does not significantly affect fitness of Svalbard reindeer.
6. Our studies are consistent with marked virulence nutritional trade-offs in this system
and highlights the need to integrate studies of parasite co-infection, interspecific
competition and community ecology to understand parasite impacts on hosts.
body mass, fecundity, macroparasites, Marshallagia marshalli, Ostertagia gruehneri, reindeer
