Prenatal social stress masculinizes the females' behaviour in guinea pigs.

This study investigated the influence of the social environment during pregnancy and lactation on the female offsprings' behaviour and body weight. The subjects studied were daughters whose mothers had lived: a) in a stable social environment (SSE) during pregnancy and lactation; b) in an unstable social environment (USE) during pregnancy and lactation; c) in a SSE during pregnancy but in an USE during lactation; d) in an USE during pregnancy but in a SSE during lactation. The SSE was made by keeping the group composition (one male, five females) constant; in the USE situation every third day two females from different groups were exchanged. After weaning (n = 4 x 3 = 12), groups of daughters, consisting of four females each, were established, originating from the different categories of mothers. From their 41st through their 80th day of age the spontaneous behaviour of the daughters was recorded in their home cages. When the mothers had lived in an USE during pregnancy, the daughters displayed significantly higher amounts of male-typical courtship, play, and social orientation behaviour compared to daughters whose mothers had lived in a SSE during pregnancy. The stability and instability, respectively, of the social environment during lactation, however, had no significant influence on the daughters' prospective behaviour. The four categories of daughters did not differ in their body weights either at birth or at 80 days of age. Thus, the instability of the social environment during pregnancy obviously represented a mild stressor that nevertheless caused a distinct masculinization of the daughters' behaviour.