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Social separation in infant Cebus apella: patterns of behavioral and cortisol response
1Laboratory of Comparative Ethology, NICHD, NIH Animal Center, Poolesville, MD 20837, USA. byrneg@mail.nih.gov
Insights
Infant tufted capuchins showed stable but attenuated behavioral and cortisol stress responses to social separation between 6 months and 1 year. Females exhibited more vocalizations and higher cortisol levels than males.
Area of Science:
- Primate behavior
- Animal endocrinology
- Developmental psychology
Background:
- Social separation is a significant stressor in many primate species.
- Understanding infant responses to separation is crucial for assessing welfare and development.
- Tufted capuchins (Cebus apella) exhibit unique social structures, including extensive allomothering.
Purpose of the Study:
- To investigate the behavioral and physiological (serum cortisol) responses of infant tufted capuchins to social separation.
- To examine the stability of these responses over a 6-month period (from 6 months to 1 year of age).
- To explore potential sex differences in response to separation.
Main Methods:
- Thirty-four infant tufted capuchins were subjected to a 2-hour social separation period.
- Behavior was recorded via video, and serum cortisol levels were measured at baseline and after separation.
- Data were collected at 6 months and 1 year of age for each infant.
Main Results:
- Separation increased passivity, locomotion, and vocalizations, while decreasing self-directed behavior and exploration.
- Both behavioral and cortisol responses demonstrated individual stability but were attenuated at 1 year compared to 6 months.
- Females vocalized more and had higher cortisol increases than males at 6 months; cortisol and behavior showed weak correlations.
Conclusions:
- Infant capuchins exhibit a relatively passive response to separation, potentially influenced by species-specific social dynamics.
- Individual differences in stress reactivity are stable during early development, though the magnitude of response may decrease with age.
- Sex differences in stress response are present in early development, with females showing heightened reactivity at 6 months.
Abstract:
34 infant tufted capuchins (Cebus apella) were separated from their social groups for a 2-hour period and videotaped in isolation at the ages of 6 months and 1 year. Baseline and 2-hour blood samples were measured for levels of serum cortisol. Compared to homecage baseline levels, passivity, locomotion and vocalizations increased during separation, while self-directed behavior and environmental exploration decreased. Both behavioral and cortisol responses to separation showed individual stability over the 6 month period, although both responses were somewhat attenuated at the later age. There was little correlation between cortisol and behavior during separations. Females vocalized more than did males during separations and showed greater cortisol increases at 6 months of age. The pattern of behavioral response seen in the 2 hours following separation appeared to be more passive than the typical 'protest' response described in many nonhuman primates, and may reflect either the physical circumstances of the separation or a characteristic of species with relaxed social bonds and considerable allomothering available to infants.