Role of steroid hormones in Trichinella spiralis infection among voles

Males are generally more susceptible to parasite infection than females. Th is sex difference may reflect the suppressive effects of testosterone and e nhancing effects of estradiol on immune function. This study characterized the role of circulating steroid hormones in sex differences after infection with the nematode Trichinella, spiralis. Because testosterone suppresses i mmune function and because polygynous males have higher circulating testost erone concentrations than monogamous males, sex differences in parasite bur den were hypothesized to be exaggerated among polygynous meadow voles compa red with monogamous prairie voles. As predicted, sex differences in respons e to T. spiralis infection were increased among meadow voles; males had hig her worm numbers than females. Male and female prairie voles had equivalent parasite burden. Overall, prairie voles had higher worm numbers than meado w voles. Contrary to our initial prediction, differences in circulating est radiol concentrations in females, testosterone concentrations in males, and corticosterone concentrations in both sexes were not related to the observ ed variation in II spiralis infection. Taken together, these data suggest t hat not all sex differences in parasite infection are mediated by circulati ng steroid hormones and that adaptive-functional explanations may provide n ew insight into the causes of variation in parasite infection.