ACCELERATION AND DECELERATION OF SEXUAL-MATURATION BY SOCIAL CUES IN A TROPICAL RODENT ZYGODONTOMYS BREVICAUDA

The effects of social cues from adult conspecifics on the rate of sexu al maturity were studied in a tropical rodent, the cane mouse (Zygodon tomys brevicauda), in the laboratory. Several aspects of the biology o f this species have suggested that it might be atypical in that young females may not accelerate or decelerate their rate of reproductive de velopment in response to social cues. This hypothesis was tested by ho using 16-day-old females with an adult male, an adult female, or alone , and reproductive development was assessed periodically, beginning wh en the mice were 20 days old. Young females paired with males underwen t more uterine growth and matured markedly earlier than did isolated c ontrols. Young females paired with adult females exhibited less uterin e growth than did isolated controls. Thus, social cues both accelerate and decelerate reproductive development in females of this species, a nd the hypothesis that social cues have no effect on reproductive deve lopment in young females was rejected. The evolutionary conditions tha t favour unresponsiveness of young females to social cues appear to be restrictive, and may be rare in mammals.