Behavioural and endocrine predictors of dominance and tolerance in female common marmosets, Callithrix jacchus

As a result of social subordination, female common marmosets undergo suppression of ovulation and inhibition of sexual behaviour. This study examined the possibility that subordination also results in decreased aggressiveness and increased submissiveness towards same-sex strangers. Thirty-two adult females were pre-assigned to eight mixed-sex social groups. The females’ behavioural and adrenocortical responses to brief confrontations with each of three female strangers were assessed under two conditions: while subjects were pair-housed with a male and while they were living in established, mixed-sex groups. Only 22% of subjects threatened stimulus females in the heterosexual pairs condition, 47% submitted and 31% showed no agonism. These agonistic behaviour patterns reliably predicted whether a female would become dominant or subordinate in a mixed-sex group. When animals were housed in established social groups, both dominant and subordinate females either showed similar responses to stimulus animals as they did in the earlier condition or became somewhat less responsive. Plasma cortisol levels did not correlate with agonistic behaviour and were not elevated by stranger-encounter testing. Finally, in the first 10 days following group formation, subordinate females that had shown ovulatory cyclicity prior to group formation were significantly more likely to receive persistent aggression from their dominant female groupmate than subordinates that had been anovulatory. These results suggest that attainment of social status between female marmosets is closely related to pre-existing individual differences in agonistic behaviour, whereas tolerance between females depends upon ovarian function. ? 1996 The Association for the Study of Animal Behaviour Dominant and subordinate individuals of many species show systematic differences in ‘personality’, as reflected in patterns of social behaviour, indices of emotionality and physiological responsiveness. For example, dominant individuals have frequently been described as more aggressive and less timid than subordinates (Fox 1972; Buirski et al. 1978; Benton & Brain 1979; Caine et al. 1983; Haug et al. 1986; Drummond & Osorno 1992) and often show lower reactivity of the stressresponsive hypothalamo-pituitary-adrenal endocrine axis (Sassenrath 1970; Ely & Henry 1978; Coe et al. 1982; Kaplan et al. 1986). Such correlations between social status and personality traits can arise through several mechanisms. First, behavioural or physiological attributes of individuals can influence the animal’s likelihood of attaining dominant or subordinate status. For example, individual differences in aggressiveness are frequently thought to influence animals’ relative likelihoods of attaining dominance (Ginsburg & Allee 1942; Wilson 1975; Slater 1986), and the ability to dominate conspecifics is heritable in some species, even when factors such as age and size are excluded as possible determinants of status (Dewsbury 1990; Moore 1990). Alternatively, behavioural and physiological differences between individuals can emerge as consequences, rather than causes, of social status. Success in agonistic interactions increases aggressiveness in several species, described as the ‘winning begets winning’ or ‘trained fighter’ phenomenon; conversely, defeat in agonistic encounters results in increased submissiveness and reduced aggressiveness, producing ‘trained losers’ Correspondence: W. Saltzman, Wisconsin Regional Primate Research Center, University of Wisconsin, 1223 Capitol Court, Madison, WI 53715-1299, U.S.A. (email: [email protected]). 0003–3472/96/030657+18 $18.00/0 ? 1996 The Association for the Study of Animal Behaviour