The goal of the present longitudinal study is to develop objective methods which allow a definition of behavioral temperament in the African green monkey or vervet (Cercopithecus aethiops sabaeus), and to determine the stability of these vectors over time. In a large captive breeding colony, newborn infants (in their birth cages) and mothers were observed systematically during the first six months of life. Within the social group, this study calls upon the methodologies standard to primate social behavioral analysis (focal animal approach), but the data is then viewed from the clinical perspective. Measures drawn from the standard primate social behavioral repertoire allowed evaluation of the frequency and quality of interaction with the mother, with peers and with other adults and of rank (in multi-infant cages). Similar social measures, as well as rank, agonistic behavior and measures of fearfulness were collected later in peer groups of 8 similarly-aged juveniles. Individual measures encompassed motility, state of arousal, modal affect, playfulness, fearfulness, exploration, etc. At 6, 9, 12 and 24 months of age, all subjects were individually assessed in a novel environment, intended in part as a complex analog of the more familiar rodent open-field test of exploration. Enrichment of this novel environment included poles, ropes, tunnels, traps and rewards. Each animal was scored with respect to motor capability, affective and physical response to the novel setting, exploratory behavior, level of inquisitiveness and problem-solving ability. Each animal was tested twice, 10 days apart, at each age point, to obtain a measure of habituation and change in performance.

The present report describes the characteristics and stability of social and individual behaviors in 78 newborns which have been tested at all time points. Preliminary results indicate that infants who consistently showed above average motility in their birth cages maintained a higher level of motility in the subsequent experimental conditions. However, those highly motile infants who also showed early signs of fearfulness in their birth cages, frequently displayed frozen immobility under the experimental conditions and showed no signs of habituation or improved performance ten days later. In addition, infants who expressed high levels of fearfulness in their birth cages, were also rated as highly fearful under the experimental conditions and showed no signs of habituation or improved performance in the repeat trial. Only those infants who were both highly exploratory in their birth cages and also had high scores for motility and outgoing, proactive behavior (e.g., initiating play fights, hanging on peer’s tails, approaching the observer) maintained a high level of exploration in the test cage. Measurement of CSF amines and metabolites, as well as circulating stress hormones, will contribute to the interpretation of these data.

The ultimate goal of this project, which will encompass some 300 newborns evaluated at all four time points, is to identify stable temperamental vectors for genetic analysis. Even in this preliminary evaluation, motility is shown to be stable from birth to age 2, unless it is dominated by fearfulness. Fearfulness is itself a stable trait from birth to age 2, and in the novel test environment, supersedes not only motility, but also such species characteristics as exploratory behavior, apparent curiosity, etc.

Supported in part by the Réseau Santé Mentale du Québec (FRSQ), the Medical Research Council of Canada and Behavioral Sciences Foundation.