Hormonal correlates of 'masculinization' in female spotted hyaenas (Crocuta crocuta). 1. Infancy to sexual maturity.

This report is concerned with hormone concentrations accompanying sexual maturation in a highly 'masculinized' female mammal, the spotted hyaena, Crocuta crocuta. Plasma concentrations of testosterone, androstenedione and oestrogen were determined by radioimmunoassay in a longitudinal study of 12 female and eight male hyaenas 2.5-62.5 months old. Concentrations of testosterone were significantly higher in males than in females after 26.5 months of age, but earlier measurements did not differ between sexes. Mean testosterone concentrations in adult female hyaenas (0.4-0.5 ng ml-1) were similar to those in several other female mammals that do not display a 'masculine' profile, but mean concentrations of androstenedione (2.5-5.5 ng ml-1) in female hyaenas were significantly higher than in males (1.0-2.0 ng ml-1), at most ages. Oestrogen could not be detected (less than 0.03 ng ml-1) in females until about 14 months of age and then increased (to approximately 0.13 ng ml-1) between 18 and 30 months; oestrogen remained undetectable in males. This rise in oestrogen in females corresponded to nipple enlargement and to changes in the size and elasticity of the urogenital meatus, permitting copulation and parturition through the clitoris. Gonadectomy (two males and four females) at 4-7 months resulted in nondetectable concentrations of testosterone and oestrogen and a marked attenuation in androstenedione (to approximately 0.39 ng ml-1), indicating that the gonads are the major source of these three steroids. Gonadectomy also eliminated sex differences in weight, nipple development and elasticity of the urogenital meatus.