Pubertal and testicular development in the common marmoset (Callithrix jacchus) shows high individual variation

Abstract. The common marmoset (Callithrix jacchus) is a New World primate that exhibits a man-like adult testicular organization. Aims: this study examines the pubertal testicular development in the common marmoset. Material and methods: immature male common marmosets (n = 48) were monitored longitudinally for a period of 13 months. Body weight and testicular volume (TV) were recorded, and testosterone levels were analyzed by an in-house radioimmunoassay. After 13 months the testes were collected, fixed and embedded in paraffin (n = 48). Histological and morphometric data were determined. Results: the first 6 months exhibited a rapid rise in body weight but not in TV. At 7 months a threefold increase in testosterone levels was observed. After 7 months the first few animals displayed rapid testis growth (> 250 mm³ at 10 months), while others exhibited no or slow pubertal development (≤ 100 mm³ at 10 months). Histological features confirmed an individually variable pattern of testicular development. Parallel with the rise in serum testosterone levels, an increase in the diameter of seminiferous tubules and an appearance of a tubular lumen as well as meiotic germ cells were encountered. The onset and the kinetics of testicular development were highly variable between individual animals in the colony. Epididymal sperm were first observed at 12 months of age. The TV and seminiferous tubule diameter showed continued growth after 12 months of age, especially in the animals developing with a delay after 7 months. Conclusions: pubertal onset in the common marmosets occurs at the earliest at 6 months of age and is hallmarked by sudden threefold increase in serum testosterone levels and a significant rise in the TV. Pubertal testis growth is characterized by an appearance of a tubular lumen and of primary and secondary spermatocytes. Spermatogenesis is qualitatively accomplished at the earliest at 12 months of age. A very high individual difference in onset and kinetics of pubertal development renders the age a very poor prognostic factor to determine the pubertal status of individual marmosets.