The influence of sex and sociality on parasite loads in an African ground squirrel

Male-biased parasite loads, which are common in vertebrates, could be a consequence of sexual selection, and for species that group, the costs of parasites could vary with group size or social structure. We examined sex-biased parasitism and the influence of group size on parasite loads in Cape ground squirrels (Xerus inauris), a highly social species that occurs in the arid regions of southern Africa. Group size did not affect numbers of ectoparasites or endoparasites. Males carried 3 times as many ectoparasites as females, but females harbored nearly 3 times as many endoparasites as males. Age class did not affect parasite loads in females, but in males, adults carried more ectoparasites than juveniles. Allogrooming was performed primarily by females, but no sex difference was found in autogrooming. Males in the subadult age class are becoming scrotal (indicating an increase in sex hormones) but typically remain in the natal group until adulthood, maintaining home range sizes comparable to adult females. Our results suggest that sexual selection does influence parasite loads in this species; increased androgen levels may reduce ectoparasite resistance in males, and smaller home ranges may increase females' exposure to endoparasites. Allogrooming could reduce ectoparasite loads of the group and mitigate the costs of grouping. Copyright 2008, Oxford University Press.