Secondary sexual coloration and CSF 5-HIAA are correlated in vervet monkeys (Cercopithecus aethiops sabaeus)

Identifying indirect markers of the physiology or neuroendocrinology of a primate can provide a powerful tool to scientists. Anecdotal descriptions and recent experimental evidence suggests that the colorful sexual skin in adult male vervet monkeys (Cercopithecus aethiops sabaeus) might be sensitive to social changes, including dominance relationships, which could be related to serotonergic activity. The present study examined whether individual differences in scrotal coloration were related to cisternal cerebrospinal fluid concentrations of 5-hydroxyindoleacetic acid (CSF 5-HIAA) in a captive population of vervet monkeys. Darkly colored males had relatively higher CSF 5-HIAA concentrations than paler males, and scrotal color hue was also related CSF 5-HIAA concentrations. These preliminary data are compatible with the hypothesis that scrotal coloration serves as an indirect marker of serotonergic activity. These findings suggest that color assessments might be useful to consider for study design, as well as for animal welfare and captive management.