Repeatability of measures of biobehavioral organization over two years in captive infant rhesus macaques, Macaca mulatta

Individual differences of infant temperament have been associated with
future health outcomes that provide explanatory power beyond adult
personality. Despite the importance of such a metric, our developmental
understanding of personality-like traits is poor. Therefore, we examined
whether young primates show consistency in personality traits throughout
development. We replicated a Biobehavioral Assessment (BBA) at three time
periods: 3-4 months, one year, and two years of age in 47 rhesus macaque
(Macaca mulatta) subjects from large mixed-sex outdoor social housing
units at the California National Primate Research Center. We report
results for tests focused on responses and adaptation to the temporary
separation and relocation, responses to a threatening stimulus, and
ratings of overall temperament. We found consistently repeatable
associations in measures of Emotionality; these associations were stronger
in males, but also present in females, and broadly consistent between year
one and two. We also explored whether behavioral responses to this
experimental relocation might be influenced by their experience being
relocated for other reasons (i.e., hospitalizations) as individuals’
responses might be influenced by similar experiences to the BBA procedure.
Only locomotion, during one of the assessments, was associated with past
hospitalization events. Overall, repeatability in Emotionality-associated
behaviors was evident across the two years, in both sexes. We did,
however, find evidence of the emergence of sex differences via
differentiated expression of behavioral responses during the BBA. We
emphasize that there is likely contextual nuance in the use of these BBA
factor-associated behaviors. Further research is required to determine
whether and how shifts occur in underlying factor structure and the
expression of associated behaviors.