ELSEVIER PII S0031-9384(96) 00051-0 Physiology & Behavior, Vol. 60, No. 2, pp. 589-594, 1996 Copyright © 1996 Elsevier Science Inc. Printed in the USA. All rights reserved 0031-9384/96 $15.00 + .00 Prenatal Social Stress Masculinizes the Females' Behaviour in Guinea Pigs NORBERT SACHSER l AND SYLVIA KAISER Westfiilische Wilhelms- Universitiit Miinster, Institut fiir Neuro- und Verhaltensbiologie, Abteilung fiir Verhaltensbiologie, Badestr. 9, D-48149 Miinster, Germany Received 27 November 1995 SACHSER, N. AND KAISER, S. Prenatalsocial stress masculinizes the females' behaviour in guinea pigs. PHYSIOL BEHAV 60(2) 589-594, 1996.--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 envi- ronment 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. Androgen Body weight Guinea pigs Individual differences Lactation Masculinization Organizational/activational effects Play Pregnancy Prenatal stress Social behaviour Social environment THE significance of social stability for health and well-being has been demonstrated numerous times in different mammalian spe- cies and by using different paradigms [ for a review see (37) ]. In stable social systems established social relationships result in predictable behaviour. As a consequence, changes in population parameters--such as a rise in individual numbers--as well as stratification into different social positions do not seem to ad- versely affect endocrine stress responses and health [e.g., (27,36,37) ]. Under conditions of social instability, however, sig- nificant increases in disease susceptibility mediated by hormonal responses are found [e.g., (2,5,21)]. Thus, for many mammals social instability constitutes a severe stressor. Stressors acting prenatally and/or during the early postnatal period of life can distinctly influence the offsprings' physiolog- ical and behavioural development as well as their reproductive functions [e,g., (8,9,15,22,23,25,33,43,44)]. In most of these studies pregnant rats and mice were subjected to nonsocial stres- sors (i.e., to regimens of heat, bright light, and restraint, respec- tively). A few investigations demonstrate similar effects of social stressors: in mice, for example, the fertility of the male offspring was clearly reduced if the mothers were kept at high densities during pregnancy (6), and in rats high population densities led to a feminization in the male offsprings' behaviour (7). To whom requests for reprints should be addressed. Recently, we conducted a pilot study with guinea pigs, which are, in contrast to rats and mice, precocial animals, and which have never before been subject to investigations on pre- and peri- natal stress. We assumed that living in an unstable social envi- ronment during pregnancy and lactation would constitute a social stressor for the females and thus should influence their off- springs' behaviour. Indeed, preliminary data suggest that daugh- ters whose mothers had lived in an unstable social environment during pregnancy and lactation showed significantly higher fre- quencies of play and male-like courtship behaviour in all-female groups than females coming from a stable social environment (19,20). Thus, the present study was conducted to elucidate whether the daughters' obvious masculinization occurred during the pre- or postnatal period of life. METHOD Subjects The guinea pigs (Cavia aperea f. porcellus) used were de- scendants of a heterogeneous short-haired and multicoloured stock of 40 animals obtained from a breeder in 1975. The animals were bred by chance in closed breeding colonies (~ 10-50 ani- mals). Through natural marking all animals were known indi- 589