Edna L. Lowe

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.

Annual cyclicity in the squirrel monkey (Saimiri sciureus): the relationship between testosterone, fatting, and sexual behavior.

The relationship between seasonal sexual activity, endogenous testosterone, and weight changes (fatting) in the squirrel monkey (Saimiri sciureus) was assessed. Adult males were shown to have an annual rhythm in testosterone levels which coincides with peak sexual activity. Fatting was shown to occur in both adult males and adult females seasonally. However, fatting preceded both heightened sexual activity and increases in endogenous testosterone concentrations. In addition the frequency of eating and drinking do not show a consistent correlation with weight change in males and females. Therefore, the seasonal fatting response in squirrel monkeys must be due to mechanisms other than altered rate of consumption or increased production of testosterone.

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.

Hormonal and behavioral changes at puberty in the squirrel monkey

Abstract Developmental changes in the reproductive behavior and physiology of 9 male and 15 female juvenile squirrel monkeys were evaluated in a 20-month study. Plasma levels of gonadal steroids remained relatively low for this species until most animals reached puberty between 2.5 and 3 years of age. Longitudinal assessment of plasma progesterone levels indicated that the onset of ovarian cycles tended to be synchronized between females although the 5 heaviest females began to cycle earlier than the rest. The heavier females reached puberty at a time which was appropriate to their birth in the wild, whereas most of the remaining females conceived 6 months later during a second period of reproductive activity that coincided with the laboratory mating season. Pubescent males underwent their first seasonal elevation in plasma testosterone levels during the second period and its onset was synchronized across all males. Thus, even in the absence of adults, pubertal processes in the squirrel monkey were strongly influenced by the seasonal breeding pattern. In addition, behavioral observations revealed that social maturation closely parallels reproductive ability in females, whereas males enter a protracted subadult stage after puberty.

Behavioral and pituitary-adrenal response of adult squirrel monkeys to mother-infant separation

Abstract (1) The behavioral and pituitary-adrenal responsiveness of adult squirrel monkeys to brief mother-infant separation was assessed. (2) The plasma cortisol levels of males and non-maternal females in an adult group and of non-separated mothers (lactating females) in a mother-infant group were determined under undisturbed basal conditions as well as after 30 min exposure to three other conditions: infant removed from its mother and separated into a small cage either next to the social group cages (Adjacent Separation) or into a small cage and carried to a separate building (Total Separation); and presentation of a strange juvenile conspecific in a small cage next to the group cages (Stranger). (3) Males showed equivalent cortisol levels after all four conditions, while both types of females exhibited significant elevations over basal levels after both infant separation conditions but not after the Stranger condition. (4) Although lactating females showed cortisol values twice as great as those of non-lactating females, the patterns of elevations were identical for the two types of females: both separation conditions produced significant cortisol elevations. Therefore, females exhibit a marked sensitivity, independent of lactation, to social signals from the agitated mother as well as the crying infant. (5) The adult group was assessed for behavioral responses, and the only significant result was an avoidance by the males of the separated infant. (6) Relationships between social status and responsiveness to the test conditions were also examined in the adult group. The dominant animal of each sex usually showed the lowest cortisol value and greatest behavioral response, while the lowest ranking animal showed the highest cortisol value and least behavioral response.

Pituitary-adrenal response to weaning in infant squirrel monkeys

This paper examines the pituitary-adrenal response of infant squirrel monkeys during the 2 weeks following the permanent removal from their mothers at the time of weaning in the laboratory. The influence of three major factors on the pituitary-adrenal response to weaning was studied: (1) preweaning experience with maternal separations; (2) familiarity with the postweaning environment; (3) preweaning social experience. The results indicated that prior separations lead to greater cortisol elevations than those observed in infants experiencing their first maternal separation at weaning. Those infants permitted to remain in their familiar social group displayed lower cortisol than did those in the novel cage alone. This was due to the social interactions and not to familiarity with the postweaning environment, since infants reared only with their mothers did not show this reduced cortisol elevation in their home environment.

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.