SOCIAL-ENVIRONMENT AND STEROID-HORMONES AFFECT SPECIES AND SEX-DIFFERENCES IN IMMUNE FUNCTION AMONG VOLES

Testosterone has bipotential effects on male fitness; that is, it both suppresses immune function and maintains characteristics important fo r reproductive success. Presumably, these effects of testosterone may be more pronounced among polygynous species because testosterone conce ntrations are generally higher among polygynous than monogamous males. The present study examined sex and species differences in cell-mediat ed immunity among four arvicoline rodents. The role of mating system a nd sex steroids in sex differences in immune function was examined in individually housed polygynous meadow (Microtus pennsylvanicus) and mo ntane (M. montanus) votes and monogamous prairie (M. ochrogaster) and pine (M. pinetorum) voles in Experiment 1. No sex differences in splen ocyte proliferation were observed among the four species and circulati ng testosterone concentrations did not correlate with immune function of individuals within each species. The contribution of social isolati on to these results was examined in Experiment 2, in which meadow and prairie voles were housed individually, or with same- or opposite-sex conspecifics in either pairs or groups of four per cage for 28 days. O verall, prairie voles exhibited more robust immune responses than mead ow voles when housed in pairs or in same-sex groups. Sex differences i n immune function were also apparent; male meadow voles had higher imm une responses than female conspecifics when housed in pairs, whereas f emale prairie voles had higher responses than male conspecifics when h oused in same-sex pairs. Circulating sex steroid hormones and corticos terone appear to mediate some, but not all, of the changes in immune f unction evoked by differential housing conditions. Taken together, the se results suggest that social factors have significant effects on imm unity and should be considered in studies of sex differences in immuni ty at both proximate and ultimate levels. (C) 1997 Academic Press.