Challenging the dogma of the ‘Island Syndrome’: a study of helminth parasites of feral cats and black rats on Christmas Island

Abstract

Many island ecosystems are exposed to ecological threats through invasive species and the parasites they harbour. Parasites can impact endemic island populations whether they are stable populations or ones already in decline. The ‘Island Syndrome’ hypothesis proposes that richness and diversity of introduced parasites differ from mainland populations with lower parasite species diversity on islands due to the founder effect. To examine the role of ‘Island Syndrome’ and impacts for faunal and human communities on a tropical island, helminth parasites were identified from feral cats (Felis catus) (n = 66) and black rats (Rattus rattus) (n = 101) on Christmas Island. Sixty-one (92 per cent) of cats and 85 (84 per cent) of rats harboured one or more helminth species with total infra-community richness (TICR) ranging over zero to six species in cats and zero to seven species in rats, including species of zoonotic significance (Angiostrongylus cantonensis, Toxocara cati, Ancylostoma braziliense, Taenia taeniaeformis, Moniliformis moniliformis and Hymenolepis nana). High parasite prevalence and TICR were expected in island populations; however, high parasite richness in cats and rats on Christmas Island was counter to the ‘Island Syndrome’. These results suggest that introduced cats and rats may be responsible for maintaining an increased parasitological threat to fauna and human communities in certain ecosystems