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

Sex-biased parasitism is found in many species, but the skew to one sex or the other varies and is 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 (Sabine, 1822)) 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, whereas 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, whereas 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 to understand the factors influencing sex-biased parasitism. Key words: Urocitellus richardsonii, ectoparasites, endoparasites, Richardson's ground squirrels, sex-biased parasitism, immunity. Le parasitisme variant selon le sexe est present chez de nombreuses especes, bien que l'asymetrie vers un sexe plutot que l'autre varie, vraisemblablement en raison de differences de comportement de l'hote et du parasite et de l'intensite de la selection sexuelle. Nous avons examine le parasitisme variant selon le sexe chez les ecureuils de Richardson (Urocitellus richardsonii (Sabine, 1822)) et postule que les males seraient plus intensement parasites que les femelles puisqu'ils sont plus gros, que leurs domaines vitaux sont plus grands et que leur agressivite et leur combativite sont elevees durant la courte periode de rut, laissent croire qu'ils pourraient reduire leur investissement immunitaire au profit d'un investissement accru dans la reproduction. Des ecureuils ont ete captures durant la periode de rut, et leurs endoparasites et ectoparasites ont ete examines. La masse corporelle, l'etat d'embonpoint et des mesures de l'immunite ont ete enregistres. La prevalence et l'abondance de nematodes etaient plus elevees chez les males, alors que la prevalence de puces etait plus grande chez les femelles. Les males avaient egalement moins de lymphocytes que les femelles, ainsi que des rapports neutrophiles:lymphocytes plus eleves. Les femelles avaient plus d'eosinophiles et un moins bon etat d'embonpoint que les males. Les charges d'endoparasites plus elevees des males donnent a penser que ces derniers compromettraient leur immunite au profit d'autres fonctions, alors que la prevalence plus elevee de puces chez les femelles pourrait etre causee par des differences entre les sexes sur le plan de la socialite. Notre etude demontre l'importance d'examiner plusieurs types de parasites pour comprendre les facteurs qui influent sur le parasitisme variant selon le sexe. [Traduit par la Redaction] Mots-cles : Urocitellus richardsonii, ectoparasites, endoparasites, ecureuil de Richardson, parasitisme variant selon le sexe, immunite.
Introduction Sex biases in parasite loads are well documented in the literature; however, the sex with the higher parasite loads appears to vary between and even within the species (Krasnov [...]