Peer and maternal influences on the expression of foot-clasp mounting by juvenile male rhesus monkeys.

Abstract

The display of adultlike foot-clasp mounts by male rhesus monkeys occurs during the 1st year of life in animals reared with their mothers in social groups where peer interaction is possible 24 hr per day. In contrast, this form of mount is rarely displayed if infants are separated from their mothers at 3 months of age and allowed daily .5-hr periods for peer interaction. To distinguish between maternal and peer access-time influences upon the development of this response, we housed rhesus monkeys with their mothers and allowed either .5-hr or 24-hr daily access to peers in the presence of their mothers during the 1st year of life. Male infants restricted to .5-hr periods with peers rarely or never foot-clasp-mounted peers, although 3 of 6 males foot-clasp-mounted their mothers. In contrast, males given 24-hr access to peers regularly mounted peers using the foot-clasp mount. Males from the 2 groups did not differ in total frequencies of all mount types displayed, only in the display of foot-clasp mounts. After maternal separation at the end of the 1st year, rearing effects on the display of mounting persisted into the 2nd year. Males that received 24-hr daily peer access during the 1st year continued to foot-clasp-mount peers whereas .5-hr males failed to do so, indicating that the experience of mounting one's mother with the adult posture was not sufficient to support peer-oriented foot-clasp mounting at a later age. In addition to deficits in peer-oriented foot-clasp mounting. .5-hr infants displayed higher frequencies of threat and withdrawal behaviors to peers and presented to peers less frequently than did infants from the 24-hr rearing condition. These results contradict a motor deficiency hypothesis to account for the rare display of foot-clasp mounts to peers by males receiving .5-hr daily access to peers during the 1st year of life. Instead, data support the view that .5-hr animals either failed to develop positive response patterns necessary for the execution of the foot-clasp mount, or learned negative patterns of social interaction that prevented the display of this cooperative behavior.