The Influence of the Social Environment on Sexual Maturation in Male Mice

Summary. Albino male mice were reared from weaning in the presence of an adult female, in the presence of an adult male, or in the absence of an adult. At 36, 48, 60 and 78 days of age, males in samples from each rearing condition were killed to assess their reproductive state. The testicular development of young males was most rapid when they were reared in the presence of an adult female. By 78 days of age, this advantage was lost when the males were compared to those reared without an adult present. In contrast to the effect of an adult female, the presence of an adult male had an inhibitory effect on testicular and accessory gland development. The inhibition was most pronounced at 78 days of age. The inhibition of sexual maturation found in this experiment contrasts with an earlier finding that the presence of males accelerates female development. This dual rôle of the male may be an important factor in the dynamics of rodent populations by increasing the availability of mature females and reducing the reproductive capabilities of potential competitors for these females.