Helminth parasitism in two closely related South African rodents: abundance, prevalence, species richness and impinging factors

We investigated patterns of helminth infection in two closely related rodents (social Rhabdomys pumilio occurring mainly in xeric habitats and solitary R. dilectus occurring mainly in mesic habitats) at 20 localities in different biomes of South Africa and asked if between-species differences were mainly caused by difference in sociality or difference in environmental conditions of their respective habitats. Helminths recovered from the gastrointestinal tract totalled 11 nematode and 5 cestode species from R. pumilio and 19 nematode and 7 cestode species from R. dilectus. In both hosts, mean abundance and prevalence of nematodes were higher compared to cestodes. Cestode infection as well as nematode abundance, species richness or prevalence did not differ between the two rodents. However, incidence of nematode infection was significantly higher in R. dilectus than in R. pumilio. Moreover, nematode numbers and species richness in infracommunities of R. pumilio inhabiting the relatively more xeric Karoo biome were significantly lower than in those inhabiting the relatively less xeric Fynbos biome. Although we could not unequivocally distinguish between effects of host sociality and environmental factors on the number of individuals and species of helminths in the two hosts, differences in the incidence of nematode infection between R. pumilio and R. dilectus as well as differences in the number of nematode individuals and species between R. pumilio from the Fynbos and the Karoo suggested the effect of environmental conditions on helminth infection to be more important than that of sociality.