Reproductive hormone profiles in captive male orangutans: Implications forunderstanding developmental arrest

For many years researchers have described some male orangutans as "subadult ." These males are of adolescent to adult age and are reproductive, but hav e Little to no secondary sexual trait development. Until now the only endoc rine study of this arrest of secondary sexual trait development was perform ed by Kingsley (1982, 1988). She found that "subadult" or arrested males ha ve lower testosterone levels than similar age developing adolescents or adu lt males. In this study, urine samples were collected over a two-year perio d from 23 captive male orangutans in order to more fully define male endocr ine profiles. Three study males were juveniles, seven were arrested adolesc ents, six were developing adolescents, and seven were mature adults. Mornin g samples were analyzed by radioimmunoassay for levels of testicular steroi ds and gonadotropins and group hormone profiles were compared by analysis o f variance. Results illustrate that arrested adolescent orangutans have sig nificantly lower testosterone and dihydrotestosterone (DHT) levels than dev eloping adolescents, but significantly higher levels than juveniles. Lutein izing hormone (LH) levels also differed between arrested and developing ado lescents, with arrested males having lower levels. However, follicle stimul ating hormone (FSH) levels were similar in both morphs of adolescent male. The overall hormone profiles for arrested and developing adolescent male or angutans suggest that arrested males lack levels of LH, testosterone, and D HT necessary far development of secondary sexual traits. However, they have sufficient testicular steroids, LH, and FSH to fully develop primary sexua l function and fertility. These endocrine data help define alternative deve lopmental pathways in male orangutans. The authors discuss the relationship between these developmental pathways and male orangutan reproductive strat egies, and hypothesize about their prepubertal socioendocrine determination . (C) 1999 Wiley-Liss, Inc.