Sex-biased parasitism in Richardson’s ground squirrels (Urocitellus richardsonii) depends on the parasite examined

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Waterman, Jane
Macklin, Gabrielle
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NRC Research Press
Sex-biased parasitism is found in many species but the skew to one sex or the other varies, most likely due to differences in host and parasite behaviour and the intensity of sexual selection. We examined sex-biased parasitism in Richardson’s ground squirrels (Urocitellus richardsonii Obolenskij, 1927) and hypothesized that males would be more heavily parasitized than females as they are larger, have larger home ranges; and display high aggression and fighting during the short mating season, suggesting that they may trade-off investment in immunity for higher investment in reproduction. Squirrels were caught during the mating season and examined for endoparasites and ectoparasites. Body mass, condition and immune measures were recorded. Males had higher nematode prevalence and abundance while females had higher flea prevalence. Males also had lower lymphocytes than females, as well as higher neutrophil to lymphocyte ratios. Females had higher eosinophils and they were in poorer body condition than males. The higher endoparasite loads in males suggests that they may be trading-off immunity while higher flea prevalence in females may be due to differences in sociality between the sexes. Our study demonstrates the importance of examining multiple parasite types in order to understand the factors influencing sex-biased parasitism.
ectoparasites, endoparasites, Richardson's ground squirrels, sex-biased parasites, immunity, ICHH