Cooperative social coordination and aggression: II. Effects of sex and housing among three strains of intact laboratory rats differing in aggressiveness

Pairs of laboratory rats were rewarded with sugar solution for cooperating by means of synchronized shuttling in a rectangular chamber. Learning and performance were compared in males and females of three strains--S3, Charles River, and Wistar--ordered in terms of decreasing levels of aggressiveness. In addition, same-sex pairs of each strain were housed either together or individually. When housed together, males and females of all strains eventually cooperated at comparable levels, with rates of acquisition across strains inversely related to their aggressiveness. Individual housing, in contrast, was associated with severe deficits in males of the S3 and CR strains linked to violent fighting and prolonged freezing by animals who had previously been defeated. All other individually housed groups, including males of the Wistar strain and females of all strains, were able to cooperate, including S3 females whose violent fighting was not associated with immobility by defeated animals. In general, the majority of groups were able to cooperate despite differences in aggressiveness associated with sex, strain, and housing. Possible processes in this accommodation are discussed.