Contextual determinants of female-female mounting in laboratory rats

Female-female mounting is widespread among mammalian species, but little is known about the proximal function of this behaviour. While such mounting i s often regarded as a 'masculine' trait, its widespread occurrence may indi cate that it serves specific functions within the context of female-female social behaviour. We valuated female mounting behaviour in Long-Evans rats in standard observation chambers and in a seminatural enclosure. Under thes e conditions, we examined a number of potential factors that might influenc e mounting, including the oestrous cycle, social hierarchy, familiarity and male presence. The female's mounting was not influenced by her own oestrou s cycle, but did vary with the oestrous cycle of the stimulus female. Socia lly dominant females mounted significantly more than subordinate females, a nd mounting by the dominant female was most frequent when the subordinate f emale was sexually receptive. Females mounted (and fought with) unfamiliar females significantly more than they did with familiar cagemates. Female-fe male mounting was dramatically reduced when males were present. Further tes ting showed that female mounting did not affect the induction of the proges tational state of pregnancy, suggesting that female mounting does not funct ion as a pseudomale behaviour that can substitute for genital stimulation p rovided by the male. Based on these data, female mounting does not appear t o function as a sexual behaviour per se, but may serve as a form of female social behaviour related to maintenance of the female's social status withi n female groups. In this regard, the results of this study suggest that fem ale mounting is part of the normal female's complex behavioural repertoire and does not necessarily reflect masculinization of some underlying neural substrate. (C) 1999 The Association for the Study of Animal Behaviour.