ADAPTIVE IMMUNE-RESPONSES ARE LINKED TO THE MATING SYSTEM OF ARVICOLINE RODENTS

Males generally exhibit reduced immune responses and greater susceptib ility to disease than females. The suppressive effect of testosterone on immune function is hypothesized to be one reason why males have low er immune responses than females. presumably, this effect of testoster one should be more pronounced among polygynous than monogamous species because circulating testosterone is higher among polygynous than mono gamous males. The present study examined the extent to which sex diffe rences in specific humoral immunity are related to the endocrine statu s and mating system of two arvicoline rodents. Humoral immunity was ev aluated among polygynous meadow voles (Microtus pennsylvanicus) and mo nogamous prairie voles (Microtus ochrogaster) by challenging them with the novel antigen keyhole limpet hemocyanin (KLH) and assessing speci fic immune responses 5, 10, and 15 d following immunization. Overall, meadow voles mounted higher anti-KLH IgM and IgG responses than prairi e voles did. Sex differences were also apparent for anti-KLH IgM respo nses; male meadow voles mounted higher antibody responses than conspec ific females, whereas female prairie voles mounted greater responses t o KLH than did conspecific males. Male meadow voles had significantly higher testosterone concentrations and reproductive organ mass than ma le prairie voles did but had elevated immune responses, suggesting tha t testosterone map not be the primary factor involved in the observed sex and species differences in immune responses. Species and sex diffe rences in corticosterone concentrations were also evident and map cont ribute to the observed differences in immune function. The influence o f extrinsic factors on immune function is also discussed. Taken togeth er, these data provide evidence that the mating system may influence e ndocrine-immune interactions.