THE SYNCHRONY OF OESTRUS IN MICE: RELATIVE ROLES OF THE MALE AND FEMALE ENVIRONMENTS

Abstract

SUMMARY The effects were evaluated of exposing female C57BL/6J mice to different male and female environments before pairing on attainment of oestrus after pairing. In Expt. I, grouped female mice were exposed for 2 days to male urine of the same strain, a different strain (CBA/J), a different species ( Peromyscus maniculatus bairdii ), or to female urine of the same strain. Male urine of the same strain accelerated attainment of oestrus; exposure to male urine of a different species did not. Results on the significance of strain specificity were inconclusive. In Expt. II, grouped females were isolated in clean cages for 2 days before pairing, with and without exposure to male urine. A high degree of synchrony was obtained on the first night after pairing in both groups (about 60% of all females which mated in 4 days). Apparently, synchrony of oestrus in grouped females is as much, or more, a result of a release from the oestrus-suppressing effects of crowding (in all-female groups) as of stimulation by the odour of the male (male urine). Synchrony after pairing was also found in two albino strains of mice (SWR/J and SJL/J) which had been reared together in small groups.