The development of sexual dimorphism in transplanted mouse pelves.

The bony pelves of adult male and female mice have several constant morphological differences that constitute a sexual dimorphism.' From birth to about 17 days of age the bony pelves of both males and females are similar morphologically and resemble those of the adult female. Sex differences in pelvic morphology first appear from 17 to 21 days of age when the male's pelvis begins to resemble that of the adult male. Male and female mice gonadectomized at birth have female-type bony pelves at the age they would normally be sexually mature. Therefore, the female type is the agonadal type and the presence of the testes is necessary for the development of the male-type bony pelvis. Male and female mice gonadectomized at birth and treated with testosterone during postnatal development have male-type pelves when adults. Thus, androgen is the factor responsible for the normal production of bony pelvic sexual dimorphism.! The presence of continually functioning testes is necessary throughout normal postnatal development up to sexual maturity in order that the bony pelvis acquire all of the morphological features characteristic of the adult male pelvis.' The present experiment was designed to determine any influence androgen may have upon the morphology of a pelvis that developed at an abnormal site. Forty-eight inbred Brown-belt mice were arranged into four groups: Group 1: Six males and six females 14 days of age; Group 2: Twelve adult male hosts bearing transplanted pelves from male littermate brothers; Group 3: Twelve adult female hosts bearing transplanted pelves from female littermate sisters; Group 4: Twelve adult male hosts bearing transplanted pelves from female littermate sisters. All of the donors were sacrificed at 14 days of age, a time well before pelvic dimorphic features appear. Their pelves were exposed and stripped of attached soft tissue. The coxal bones were then separated from the sacrum at the sacroiliac joints. Each excised bony pelvis, consisting of the two coxal bones and intact pubic symphysis, was transplanted subcutaneously by placing it under the skin of the back of either a 14-day-old brother or sister littermate that served as a host until they were sacrificed when sexually mature at 60 days