Effects of prepubertal habitation conditions on the reproductive physiology of the male house mouse.

Abstract

Summary. Male albino and wild house mice were reared from weaning (at 21 days) either to 37 or 56 days of age in: (1) isolation, (2) all-male groups of four, or (3) all-male groups of four in cohabitation with an adult female. At 37 days the cohabiting albino males exhibited larger testes and epididymides than animals in the other two situations. Similarly, they had larger seminiferous tubules and were significantly more mature (by an arbitrary rating system) than the isolated males or the males in all-male groups. Wild males reared in isolation or in cohabitation were reproductively superior in essentially the same fashion to males in all-male groups. Cohabiting wild males, however, were significantly more mature than wild males in either of the other two conditions. When reared to 56 days, albino males in cohabitation exhibited a high degree of social conflict and were reproductively inferior to both the isolates and the males in all-male groups. In contrast, cohabiting wild males at 56 days of age showed reproductive growth equal to that of males in all-male groups. However, both albino and wild adult males in cohabitation exhibited none of the reproductive advantages seen in 37-day-old cohabiting males. In a final set of studies it was shown that albino males reared to 37 days of age with intact females had larger testes, epididymides and seminiferous tubules and significantly higher concentrations of epididymal spermatozoa than male litter-mates reared with ovariectomized females. Wild males reared with intact females, while failing to show larger testicular and epididymal weights, did possess larger seminiferous tubules than wild males with ovariectomized females. Those studies show that the presence of an intact female bestows reproductive advantages upon groups of young male mice. These advantages do not persist to adulthood.