Sally P. Mendoza

Mother infant attachment in the squirrel monkey adrenal response to separation

The pituitary-adrenal response following separation was evaluated in mother and infant squirrel monkeys. Four mother-infant pairs and a pregnant female, living in a social group, were the subjects of this experiment. The plasma cortisol levels of the mothers and infants were determined after the following conditions: (1) basal levels at 1100 hr, (2) 30 min after momentary separation and reunion, (3) 30 min after infant removal from the group, and (4) 30 min after mother removal from the group. The levels of plasma cortisol were significantly elevated in both mothers and infants following separation and the response was not reduced by the presence of familiar animals (e.g., separated infants which were “aunted” by the pregnant female). Separation followed by immediate reunion did not result in elevated values. These data indicate that a specific attachment relationship develops between mother and infant, and that the agitation following separation is reduced only by reunion with the object of attachment.

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 individuals physiological state and that existing relationships further determine the individuals hormonal response to the introduction of new group members.

Social status constrains the stress response in the squirrel monkey.

Abstract The influence of dominance on the pituitary-adrenal and gonadal systems was evaluated in male squirrel monkeys. Basal and stress levels of plasma cortisol and testosterone were determined in eight male pairs across a 5-week period. The data indicated that squirrel monkeys have unusually high levels of steroid hormones in comparison to other species. Dominant males had higher levels of cortisol and testosterone and showed a smaller stress response than did subordinate males.

Seasonal variations in gonadal hormones and social behavior in squirrel monkeys

Abstract The relationship between seasonal behavioral and physiological changes in the squirrel monkey (Saimiri sciureus) was examined. Seasonal changes were observed in all behaviors involved in the copulatory sequence. Social organization was slightly altered during the breeding season due to an increase in the frequency with which monkeys were in proximity to one another. Dominance relations were apparent throughout the year and did not intensify during breeding, contrary to earlier reports. Play behavior was inversely related to breeding activity, reaching unexpectedly high levels during the nonbreeding months and dropping out completely during the breeding months. Both males and females showed dramatic seasonal variations in gonadal activity. The data also indicated that seasonal variations in social behavior were mediated by physiological changes in the recipient rather than the initiator of the interaction.

Separation distress and attachment in surrogate-reared squirrel monkeys ☆

Abstract Surrogate-reared infant squirrel monkeys were exposed to various conditions of separation from their surrogate. Infants showed significant increases in plasma levels of cortisol when they were placed in an unfamiliar environment during the separation period. Changes in behavior, but not cortisol, were observed under conditions in which the surrogate was removed and the infant left in the home cage. These results differ from those previously obtained with mother-reared infants. It is concluded that surrogate-reared infant squirrel monkeys do not show the same separation response or attachment to their rearing figure as do mother-reared infants.

Social Organization and Social Behavior in Two Subspecies of Squirrel Monkeys (Saimiri sciureus)

Social organization and social behavior were examined in two subspecies of squirrel monkeys which differ markedly in the degree of sexual dimorphism. The Bolivian squirrel monkeys, the subspecies with greater sexual dimorphism, manifested a sexually segregated form of social organization, while the social organization of the Guyanese monkeys was sexually integrated. Dominance relationships were found to reflect these patterns of sexual segregation or integration; in the Bolivian social groups separate linear dominance hierarchies were established within each sex while the Guyanese monkeys established a single linear hierarchy which included both males and females. Relationships between males and females in the two subspecies appear to be regulated by two distinct mechanisms, dominance in the Guyanese monkeys and sexual segregation in the Bolivians.

Scent-Marking and Olfactory Investigatory Behavior in the Squirrel Monkey ( Saimiri sciureus )

Olfactory-related behaviors were observed in social groups of Guyanese squirrel monkeys ( Saimiri sciureus ) during three distinct phases of the annual reproductive cycle. Olfactory investigation of females and environmental objects by males showed marked increases in frequency from the nonmating to the mating season and intermediate levels during a period of transition from mating to nonmating. Olfactory investigation by females also showed evidence of seasonality, though females engaged in investigatory behaviors less frequently than did males. Females sniffed environmental objects and the anogenital area of other females more often during the mating season than during either of the other two observation periods. The frequency of three probable scent-marking behaviors (rump rubbing, back rubbing, and urine washing) showed no evidence of seasonal variation. Overall, females rump-rubbed more than males, and males back-rubbed more than females. These data suggest that olfactory investigation of females by males is an important component of reproductive activities in the squirrel monkey. The seasonal pattern of male investigatory behavior does not appear to result from an increase in female scent marking during the mating season. Rather, it seems likely that female odors change during this phase of the reproductive cycle so as to provoke increased investigation by males.

Androgen-related behavior in the squirrel monkey: An issue that is nothing to sneeze at

This study investigated a purported scent-marking behavior, sneezing, in the squirrel monkey. Sneezing occurred more often in males than in females, varied in frequency with the phase of the reproductive cycle in both males and females, and was positively correlated with male testosterone levels during the period when the most sneezing occurred. These results suggest androgen involvement in sneezing and are consistent with the notion that sneezing is a scent-marking behavior in this species.