Female spotted hyenas exhibit male-like genitalia and dominance over m
ales. Hyena ovarian tissues incubated in vitro produced large quantiti
es of the steroid hormone precursor androstenedione. The activity of a
romatase, which converts androstenedione to estrogen, was one-twentiet
h as great in hyena versus human placental homogenates. In comparison,
the activity of 17beta-hydroxysteroid dehydrogenase, which converts a
ndrostenedione to testosterone, was equal in the two homogenates. The
limited aromatase activity may allow the hyena placenta to convert hig
h circulating concentrations of androstenedione to testosterone, which
results in virilization of the fetal external genitalia and possibly
destruction of fetal ovarian follicles. Androstenedione production by
residual ovarian stromal cells during reproductive life accounts for t
he epigenetic transmission of virilization in female spotted hyenas.