The physiological response to group formation in adult male squirrel monkeys

Abstract

(1) Formation of bisexual groups during the nonbreeding season has been shown to induce breeding in primates. The hormonal response to group formation affects adult males differentially depending on the relative dominance status of the individual. (2) In this study, testosterone and cortisol levels in adult male squirrel monkeys were assessed in three conditions: prior to group formation, following formation of male groups and following introduction of females to the male groups. (3) Hormonal levels prior to group formation could not be used to predict subsequent dominance status, but following formation of male groups hormonal levels and dominance status were found to be correlated. (4) Formation of bisexual groups did induce breeding and further differentiated the males' hormonal state depending on the relative dominance status of each male. (5) The results indicate that the formation of social relationships influences each individual's physiological state and that existing relationships further determine the individual's hormonal response to the introduction of new group members.