We investigated the importance of the MHC-constitution (major histocompatibility complex-constitution) on the endoparasite load in free-range hairy-footed gerbils (Gerbillurus paeba) in the southern Kalahari Desert. While the number of alleles of the duplicated DRB exon 2 gene had no significant effects on the individual status of being 'not infected' or 'infected' and on the number of helminth morphotype infections per individual, it significantly affected the faecal egg count values. One allele (Gepa-DRB*15) was only found in uninfected mice. Our results support the hypotheses that MHC polymorphism in G. paeba is maintained by pathogen-driven selection. The present study is the first investigation on associations between duplicated DRB gene loci and the parasite load in mammals.

As a consequence of environmental change, it is expected that shifts in temperature and precipitation patterns will infl uence parasite communities and their hosts with unpredictable impact. Parasites play a vital role in ecosystems but there is only limited quantitative data which describe the eff ects of environmental parameters under natural conditions. We investigated the infl uence of rainfall, relative humidity and temperature on the prevalence, abundance and infection intensity of nematodes in southern Africa by studying the gastro-intestinal helminth community of the striped mouse Rhabdomys pumilio. Along a precipitation gradient from the Cape of South Africa to northern Namibia we trapped 470 mice over a geographical distance of about 1400 km. Faecal egg counts of 439 sampled individuals and dissections of 161 gastro-intestinal tracts revealed 15 diff erent helminth species. Th e most abundant nematode species harboured in 62.6% of all infected mice were the oxyurid Syphacia obvelata followed jointly by two species (Heligmonina spira and Neoheligmonella capensis) of the subfamily Nippostrongylinae (43.7%). We found a signifi cant positive correlation between mean annual precipitation (rainfall and relative humidity) and nematode infestation rates of animals and a negative correlation with temperature. In addition, we found associations between precipitation and diff erent qualitative measurements of parasite burden (mean nematode species richness, mean number of nematode worms and infection intensity per individual host). Th e similarity in nematode species composition decreased with distance between all study sites. Our study indicates for the fi rst time an association between climatic variables and parasite prevalence and abundance along a continuous natural climatic gradient in a small mammal. Th ese results might be incorporated in the development of models which can predict possible threats for the balance of ecosystems and shifts in infestation patterns due to global changes.

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