Social buffering of the cortisol response of adult female guinea pigs.

When housed in spacious, mixed age/sex colonies, male guinea pigs form small harems of females with which attachment-like social bonds are established. A previous study indicated that the bonded male, but not an unfamiliar male from the same colony, could reduce the plasma cortisol response of a female when exposed to a novel environment. We examined the effect of several classes of social partners on the cortisol response of females maintained under standard laboratory housing conditions. Eight "artificial harems" comprised of one adult male and two adult females were formed in standard group-housing cages 2 weeks prior to the study. Behavior observed in these home cages indicated that interactions between males and females of the triads were overwhelmingly positive in nature. When exposed to a novel environment for 2 h, the presence of either the male or female cage mate reduced the subject female's plasma cortisol response, whereas the presence of an unfamiliar adult male did not. Changes in plasma cortisol levels were not predicted by the frequency of various social behaviors observed in the novel environment. These findings: (1) demonstrate that the buffering effect of male partners on the cortisol response of adult females can be observed in guinea pigs maintained in conventional laboratory housing; (2) indicate that unfamiliar adult males are ineffective at reducing cortisol responses of females under these conditions; and, (3) appear to be the first to show buffering effects by adult female guinea pigs on the cortisol responses of other adult females.