Effects of social experience on the behaviour of male guinea pigs and rats

Abstract

Most animals have some social experience, and in non-solitary species social experiences may be frequent and various. Evolutionary theory predicts this experience should lead to changes in behaviour which maximise inclusive fitness. However, the effects of such experience on subsequent behaviour are largely unknown. Investigation of the effects of social experience on behaviour requires examination of the nature, causes and functions of social behaviour and organisation under natural and experimental conditions. In a semi-natural colony of guinea pigs, a male dominance hierarchy was found. Comparison of dominance status with social behaviour suggested that agonistic experience determined subsequent agonism and (to a lesser extent) courtship. Both sexes apparently responded to males according to physical and behavioural cues indicative of resource holding power (Parker, 1974). Early experience has often been studied in attempts to find critical periods for socialization. Isolation of rats during the post-weaning period of social play has long-term effects on some non-social and agonistic behaviours (Einon et al, 1981; Wahlstrand et al, 1983). Early isolation of non-playing rodents (including guinea pigs) has no long-term effects on non-social behaviour (Einon et al, 1981). This suggests that social play might be important in the socialisation of playing species. The effects of both isolation and experience of females on male rat behaviour was examined. Early-isolated rats showed abnormalities in intra-group social behaviour, but no increase in aggressiveness. No group studied had a consistent social organisation. Parallel experiments with guinea pigs showed increased intra-group aggressive intensity, but no other differences in social behaviour or organisation. Prolonged grouping increased individual differences in aggressiveness under all conditions, but dominance hierarchies were only formed when females were present. Reduced courtship by subordinates was apparently due to both direct and indirect effects of agonistic experience. These findings are discussed in terms both of the causes and functions of behaviour, and of the social ecologies of the two species.