The Effects of Neonatal Treatment with Tamoxifen on Sexually Dimorphic Behavior and Morphology in Gray Short-Tailed Opossums (Monodelphis domestica)

Abstract

The effects of postnatal exposure to the antiestrogen tamoxifen on sexually dimorphic behavior and morphology in adult male and female gray short-tailed opossums were examined. Following gonadecomy and treatment with estradiol in adulthood, neonatally tamoxifen-treated (TX) females showed less female-typical screeching threat behavior and TX males showed less male-typical precopulatory behavior than same-sex controls. While testes failed to descend and phalluses were shorter in juvenile TX males than in juvenile control males, behavior did not differ between TX and control animals following treatment with testosterone in adulthood. The findings that activity level following treatment with estradiol in adulthood and body weight in juveniles and adults were significantly higher in TX than in control animals of both sexes suggest that perinatal estrogens are involved also in the organization of these characteristics. The significance of these findings is discussed with respect to the development of sex differences in behavior and morphology in eutherian mammals.