Growth and reproductive development in the male tree shrew (Tupaia belangeri) from birth to sexual maturity.

The growth and reproductive development of the male tree shrew were studied from birth to sexual maturity. An infantile phase from birth to Day 30 was characterized by the rapid involution of the testis and adrenal gland from a fetal condition followed by a nadir in testosterone levels and slow growth and differentiation of the testis and accessory sex organs. The initiation of puberty occurred collaterally with the emergence of the young from the nest and was marked by a sharp rise in testosterone levels from Days 30 to 35 to maximum levels at Days 40-55. Peak testosterone levels were temporally correlated with the onset of maximum growth and differentiation of the testis and accessory sex organs, descent of the testis, development of the scrotum, and a pronounced peak in the weight-velocity curve. The rapid growth of males at puberty contributed to a moderate degree of sexual dimorphism in this species. Puberty was attained at about Day 90 with the completion of spermatogenesis and the functional differentiation of the accessory sex organs. The postnatal development of the tree shrew conforms with the general primate pattern. The precise endocrine correlates established during puberty make Tupaia belangeri a useful small animal model for the study of puberty in primates.