Different social bonds produce differential effects on behaviour and physiology in mongolian gerbils

Mongolian gerbils are socially monogamous, group-living rodents, with a social organization based on a stable reproductive pair. In the present study, the effects of social bonds in gerbil female social behaviour as a function of partner presence were investigated. Female aggression was tested against same-sexed intruders as a function of pairing with a male: before pairing females displayed very low aggression, while aggression was dramatically increased after pairing. Female preference towards the partner as opposed to an unfamiliar male was assessed in a social preference paradigm. Females showed a strong partner preference, exhibiting aggression selectively towards the unfamiliar male and affiliation exclusively towards the partner. To test for the specificity of the pair bond, the effects of a different social attachment were also examined. Sisters housed in pairs were tested against female intruders. Housing with a sister did not induce the increase of aggression seen in females paired with a male. Furthermore gerbils were subjected to a social bond disruption paradigm, followed by a free exploration test. The separation of male/female pairs decreased marking rate and ventral gland size in males, whereas no alterations were detected in females. In contrast, following the breaking of female/female pairs, behavioural and physiological effects suggestive of reproductive activation were detected in females. Overall the present results suggest the existence of a pair bonding mechanism in females which was previously claimed to be sexually dimorphic, i.e. exclusive to male gerbils, but they also confirm that the disruption of the female/male bond affects only the behavior and physiology of the male.