title: Experimental manipulation reveals few subclinical impacts of a parasite community in juvenile kangaroos.
abstract: Large mammalian herbivores are commonly infected with gastrointestinal helminths. In many host species, these helminths cause clinical disease and may trigger conspicuous mortality events. However, they may also have subclinical impacts, reducing fitness as well as causing complex changes to host growth patterns and body condition. Theoretically, juveniles should experience significantly greater costs from parasites, being immunologically naive and undergoing a significant growth phase. The aims of our study were to quantify the subclinical effects of helminths in juvenile eastern grey kangaroos (Macropus giganteus), which commonly harbour large burdens of gastrointestinal nematodes and are susceptible to associated mass mortality during cold, wet conditions. We conducted a field experiment on a population of free-ranging kangaroos, removing nematodes from one group of juveniles using an anthelmintic treatment. We then compared growth parameters (body condition and growth rates) and haematological parameters of this group with an age-matched, parasitised (untreated) control group. Treated juvenile kangaroos had significantly higher levels of plasma protein (albumin) but, contrary to our predictions, showed negligible changes in all the other parameters measured. Our results suggest that juvenile kangaroos are largely unaffected by their gastrointestinal helminth burdens, and may be able to compensate for the costs of parasites.
authors.affiliation: Department of Zoology, The University of Melbourne, VIC 3010, Australia ; Faculty of Veterinary Science, The University of Melbourne, Veterinary Clinical Centre, Werribee, VIC 3030, Australia.
authors.forename: Jemma
authors.initials: J
authors.lastname: Cripps
authors.affiliation: Faculty of Veterinary Science, The University of Melbourne, Veterinary Clinical Centre, Werribee, VIC 3030, Australia.
authors.forename: Ian
authors.initials: I
authors.lastname: Beveridge
authors.affiliation: Faculty of Veterinary Science, The University of Melbourne, Veterinary Clinical Centre, Werribee, VIC 3030, Australia.
authors.forename: Richard
authors.initials: R
authors.lastname: Ploeg
authors.affiliation: Department of Zoology, The University of Melbourne, VIC 3010, Australia.
authors.forename: Graeme
authors.initials: G
authors.lastname: Coulson
keywords: Costs; Haematology; Helminths; Juveniles; Macropus giganteus; Parasites