Effects of restocking rabbits on the helminth fauna of wild rabbit populations in the northwest Iberian Peninsula

Between June 1995 and March 1998, 172 wild rabbits from several sites in the northwestern Iberian Peninsula (Galicia) were captured and their helminth fauna examined. Seventy-six were from areas that had been restocked with rabbits from other Iberian regions, or with wild/domestic rabbit hybrids ("restock rabbits") and 96 from areas that had not ("native rabbits"). Twelve species were found, of which Mosgovoyia pectinata and Taenia pisiformis (cysticerci) exhibited significantly greater prevalence (Fisher's Exact test; Pless than or equal to0.05), mean intensity and mean abundance in native rabbits (ANOVA, P<0.05) for M. pectinata. Dermatoxys hispaniensis and Leporidotaenia pseudowimerosa were present only in native rabbits, with very low prevalence. The remaining species exhibited greater parasite burden values in restock rabbits, significantly so for Trichostrongylus retortaeformis (ANOVA, U-test), Graphidium strigosum (ANOVA) and Leporidotaenia wimerosa (U-test). It is concluded that no new helminth species (except, perhaps, Nematodirus zembrae) have been accidentally introduced, but that restock rabbits are apparently less resistant to the native stocks of some helminth species, which possibly reduces their fitness for survival.