Behavior and progesterone levels in Callithrix jacchus females

In callitrichids, and especially in the Callithrix and Saguinus genera, reproductive suppression maintains the breeding exclusivity of dominant females. It has been suggested that dominance may be inferred from agonistic behavior of females. The purpose of this study was to assess the adequacy of behaviors as indicators of hormonal status in Callithrix jacchus females. Two pairs of twin females were observed for affiliative, agonistic and sexual behaviors for 20 weeks, in four stages of increasingly potential competition for one male. During the same period, blood samples were taken regularly for progesterone determination by ELISA. The two pairs differed markedly as to behaviors and hormonal status: pair 1 showed a well established behavioral dominance and only one ovulating female from the beginning of the observation period; pair 2 showed competition for dominance until the last stage of observation, when one of the females started ovulating. Correlations between behaviors and progesterone levels showed differences between subordinate and dominant females mostly in pair 2. Although limited in number of animals studied, these results suggest that there is a relationship between behavior and hormones in female marmosets, but this relationship may be useful in the identification of the physiological status of females only in groups where the dominance is not well established.