MICE REARED WITH RATS: MODIFICATION OF BEHAVIOR BY EARLY EXPERIENCE WITH ANOTHER SPECIES.

Mice in group 1 (controls) spent all their lives with other mice. Mice in group 2 had experience only with male and female rats after weaning; group 3 mice had no experience with peers-each litter was reduced to one pup, which was reared in isolation after weaning; group 4 mice were fostered to a lactating rat mother at approximately 3 days of age and thereafter lived only with rats. In adulthood group 4 mice were the least active and group 3 the most; mice in groups 2 and 4 preferred to spend time in a chamber adjacent to a rat, those from groups 1 and 3 in a chamber containing another mouse; when mice were paired off within experimental groups and given the opportunity to fight each other, the percentage of pairs in which 4 were, respectively, 44,27,100, and 0.