Sexual maturation in the Australian rodent Rattus fuscipes assimilis

Abstract

Historically, the standard for reproductive biology in Rattus has developed from extensive investigations of laboratory stocks of R. norvegicus. Our descriptive study of the development of the gonads and the accessory sex glands in laboratory-reared R. f assimilis compares time of maturation of these organs in the two species and demonstrates that specific events vary to some extent in both absolute and relative timing in the two forms. Although the time of sexual maturation is similar in the two species, certain of the precursors to full spermatogenic activity appear variously later in assimilis than norvegicus. In both species the laboratory stocks mature a month or more earlier than do their counterparts in wild populations, suggesting that norvegicus and assimilis are vulnerable to natural environmental or social influences that in the wild suppress the genetic potential for earlier sexual maturation.