Development from birth to sexual maturity in a semi-free-ranging colony of mandrills (Mandrillus sphinx) in Gabon.

This report presents information collected over 7 years (1983-1990) in Gabon, on a breeding group of 14, increasing to 45, mandrills maintained in a rainforest enclosure. Under these conditions, a seasonal cycle of mating (June-October) and birth (January-May) occurred. Females began to exhibit sexual skin swellings at age 2.75-4.5 years (3.6 +/- 0.6 years, mean +/- SD; n = 10) and first delivered offspring when 3.25-5.5 years old (4.4 +/- 0.8 years; n = 9). Gestation periods ranged from 152 to 176 days (167 +/- 9 days; n = 6 accurately dated pregnancies) and interbirth intervals from 11 to 15 months (12.4 +/- 1.3 months; n = 15). Females could reproduce 2 years before attaining adult body weight (10-15 kg) and complete dental eruption by 5.0-5.5 years. Males, by contrast, developed more slowly, reaching adult body weight (30-35 kg) and testicular volume (volume of left testis: 25-30 ml) at 8 years. Consistently high circulating testosterone concentrations (8.17 +/- 2.0 ng ml-1) could be measured by 9 years of age. Fully developed males exhibited fatting of the rump and flanks, as well as striking sexual skin coloration and an active sternal cutaneous gland; little expression of these features was evident during pubertal development. Marked individual age differences occurred with regard to the onset and complete development of these features, suggesting possible interactions between social environment and physical maturation.