Age-related changes in fecal adrenal androgen levels in hylobatids

Adrenarche, or the postnatal activation of the adrenal gland, is a phenomenon exclusive to some primates that is evidenced by high levels of the hormones dehydroepiandrosterone (DHEA) and its sulfated form (DHEAS), independent of the onset of puberty. Within primates, two patterns of adrenal secretions occur: a prepubertal increase in DHEAS levels (adrenarche) that has been reported in humans and great apes, and a continuous postnatal decline on DHEAS levels with age, observed in cercopithecines (e.g., macaques and baboons). Our research seeks to determine the pattern of DHEAS secretion during hylobatid development. DHEAS was measured by enzyme immunoassay in cross-sectional fecal samples from 35 female and 29 male zoo-housed hylobatids (Hylobates, Nomascus, Symphalangus) ranging from age 1 to 54 years. Additionally, we measured longitudinal fecal samples from 7 female hylobatids under human care (6 Nomascus, 1 Hoolock). Our study tested the effects of age, sex, and genus on fecal DHEAS levels using generalized linear mixed-effects models. The models were separated by genus and showed that age was positively correlated with a prepubertal increase in fecal DHEAS across all genera, indicating that the hylobatids exhibit delayed adrenarche. A significant effect of sex was only identified in the Symphalangus model. Results from adult and old hylobatids did not exhibit decreasing DHEAS associated with adrenal senescence, which is characteristic of humans and other primates. The evidence of a delayed DHEAS increase observed across all hylobatid genera suggests a shared developmental characteristic among all ape species.