Close Proximity of the Heterosexual Partner Reduces the Physiological and Behavioral Consequences of Novel-Cage Housing in Black Tufted-Ear Marmosets ( Callithrix kuhli )

The present studies assessed the extent to which heterosexual pairmates could buffer marmosets (Wied's black tufted-ear marmoset, Callithrix kuhli) against stress. Six male and six female marmosets from established groups were exposed to two experimental manipulations together with a control condition. Each condition lasted a total of 4 days. For the two experimental conditions, animals were removed from the family group and housed in a novel cage for 48 h in either the presence or the absence of the heterosexual pairmate. During the 48-h novel-cage housing period and for 48 h upon reunion of the subjects with the family group, concentrations of urinary cortisol were measured in the first void sample of the day and behavioral observations were conducted. When animals were housed alone in a novel cage they exhibited significant elevations in levels of urinary cortisol after 24 and 48 h of novel-cage exposure. In contrast, when marmosets were housed in the novel cage in the presence of the pairmate, levels of urinary cortisol did not change across the 4-day period. The presence of the social partner also reduced the behavioral manifestations of exposure to novelty. Upon reunion with the family group, animals that had been housed in the novel cage alone spent significantly more time in close proximity to the pairmate than animals that had been housed with the partner. A second experiment was conducted to determine the effect that separation from the pairmate, only (independent of any effects of novelty), had on levels of cortisol. Concentrations of urinary cortisol were measured in subjects housed in the familiar home cage, but in the absence of the pairmate, over a 48-h period and compared to concentrations of excreted cortisol immediately prior to separation. Separation from the pairmate did not elevate cortisol levels when the subject was housed in the home cage, suggesting that elevated cortisol levels in animals housed alone in the novel cage were in response to novelty exposure rather than to separation from the pairmate. Since the physical presence of the heterosexual partner reduced the physiological and behavioral effects of novel-cage housing, social attachments might function as homeostatic regulators of HPA function in marmosets.