Gayle Byrne

Cortisol reactivity and its relation to homecage behavior and personality ratings in tufted capuchin (Cebus apella) juveniles from birth to six years of age

Rank correlations between cortisol reactivity measures (baseline, 2 h stress peak and change from baseline) at 6 months and 1 year and (1) behaviors videotaped in the home cage and (2) subjectively judged personality ratings were examined in 36 juvenile tufted capuchins from birth to 6 years of age. High cortisol reactivity was associated with both lower levels of play and exploration in the home cage, and higher levels of proximity and contact with mothers. Animals with higher baseline cortisol played by themselves more, and played with other animals less, than did those with lower baselines. High cortisol reactivity, especially at 1 year of age, was also related to higher levels of dorsal carrying by mothers in the second year, when most infants are independent of mothers. Ratings on the personality traits, Aggressive, Confident, Curious, Effective and Opportunistic, were all negatively correlated with cortisol reactivity levels, while Apprehensive, Fearful, Insecure, Submissive and Tense were positively correlated with cortisol reactivity. In summary, there was a relationship between high physiological reactivity and inhibited, fearful behavior and temperament patterns not previously described in capuchins.

Handedness and cortisol in tufted capuchin monkey infants.

In this research, we examined the relationship between handedness and levels of plasma cortisol in infant monkeys (Cebus apella). Specifically, we sought to test the hypothesis that stress functioning is related to hemispheric specialization and is manifested in a positive correlation between cortisol levels and the frequency of right- versus left-hand use. We found a significant relationship between stress cortisol at age 6 months and lateral bias towards greater use of the right versus left hand at ages 6 and 12 months. These data suggest an early developmental influence of stress reactivity on the emergence of hemispheric specialization for manual control in infant monkeys through the 1st year of postnatal life.

EARLY LATERAL BIAS IN TUFTED CAPUCHINS (CEBUS APELLA)

We investigated the development of lateral bias in infant tufted capuchins (Cebus apella) by recording head orientation during the first 2 postnatal weeks and hand preference during Weeks 23 to 24 and 47 to 48. We found that lateral bias for head orientation at 1 to 2 weeks was negatively related to hand preference at 23 to 24 weeks. Further, we found population-level left-hand preferences at both 23 to 24 and 47 to 48 weeks, and that hand preference at 23 to 24 weeks is positively correlated with hand preference at 47 to 48 weeks. We also noted a trend toward a sex difference in the direction of neonatal head orientation, with males exhibiting a left-side preference and females exhibiting a lack of preference toward either side. Our findings differ from those obtained in studies with developing humans and chimpanzees in two important ways. First, the trend for head orientation and hand preference in infant capuchins was to the left rather than to the right. Second, we found a negative relation between direction of early head orientation and subsequent hand preference. It seems likely that research examining cerebral development in capuchins will help us to better understand the occurrence of left-handedness and the development of cerebral dominance in humans.

Twinning in Tufted Capuchins (Cebus apella): Rate, Survivorship, and Weight Gain

We calculated the rate of twinning across four captive collections of tufted capuchins (Cebus apella) to be 2.4%. This rate contrast with previous reports that twinning in tufted capuchins is rare. Additionally, we present data on the survival and weight gain of twins in this species as compared to singletons. Twins face their greatest risk of mortality on or before the first day of life, when 45% will die compared to 16% of singletons. After the first day of life, twins and singletons demonstrate comparable survival rates. This, in conjunction with the finding that at no time during the first year of life do twins and singletons differ significantly in their weights, suggests that twinning is a viable reproductive form for these animals, especially in the captive setting where nutritional demands are met.

Relationship of early infant state measures to behavior over the first year of life in the tufted capuchin monkey (Cebus apella)

Data on activity states were collected from 29 group‐housed capuchin monkey (Cebus apella) infants for 3 h each week from birth to 11 weeks of age. The amounts of time spent in sleeping/drowsy, alert–quiet, and alert–active states were measured in these subjects. Videotaped observations of these infants were recorded 3 times/week in the home cage over the first year of life and were scored for a number of social and exploratory behaviors. The extent to which early infant activity state scores predicted later behavior in the home cage was examined. Infant state measures correlated significantly with home cage behavior during months 2–6 in that infants that had been more active in early infancy spent more time alone, with other animals, and in exploration and play and less time with mothers than did quieter infants. Early state measures were less successful in predicting home cage scores beyond 8 months of age, whereas differences in behavior attributable to housing variables became more salient in the latter part of the first year. There was also a negative correlation between mother and infant activity in months 2 and 3, in that more sedentary mothers tended to have more active infants. Am. J. Primatol. 44:43–56, 1998.

Intimate social behavior in infant interactions in Cebus apella.

The development and individual stability of three intimate social behaviors (Lipsmacking, Carrying Attempts, and Facial Inspection) were examined for 43 group‐housed Cebus apella infants from birth to 2 years of age. Occurrence of these behaviors was scored from 10‐min videotape samples recorded three times a week over that time. Frequency of Lipsmacking and Carrying Attempts by adult males, adult females, and juveniles were all highest in early months and decreased to low levels by the end of the first year. Facial Inspection of partners by infants, in contrast, first began at 3–4 months and increased over time, at least to adult males and juveniles. Correlational analyses indicated stable individual differences in these interactions with infants and outlined a relationship between these intimate behaviors and more general social patterns reported previously for these animals. Results suggest that adult males may play a special role in affording juveniles opportunities for social learning of foraging and manipulative skills. Am. J. Primatol. 71:77–85, 2009. Published 2008 Wiley‐Liss, Inc.