Importance of gender for the display of social impairment in pairbond disrupted gerbils N.J. Starkey ² , C.A. Hendrie ‡, * a Department of Psychology, University of Central Lancashire, Preston, PR1 2HE, U.K. b Department of Psychology, University of Leeds, Leeds, LS2 9JT, U.K. Abstract Gerbils form stable male/female pairbonds. Disruption of these has been shown to have consequences for subsequent social behaviour. The response in males is typically a decrease in the initiation of social contacts, whilst females typically freeze when approached. The current studies examined the influence on these phenomena of the gender of the stimulus animal. Data revealed that a similar increase in immobile- in-contact was seen in pairbond disrupted females regardless of whether they were interacting with males or females. By contrast, reductions in social behaviour were only seen in males when interacting with other males. Social investigation was increased when interacting with females. These results are interpreted in the context of gerbil social organisation in the wild. That is, whilst females continue to represent a possibility for opportunistic mating, decreased social investigation and offense directed towards other males indicates a reduced capacity for territorial defence. Together, present findings demonstrate that there are clear sex-differences in the behavioural effects of pairbond disrup- tion in gerbils but that it is only in males that the expression of these effects is influenced by the sex of the stimulus animal.  1998 Elsevier Science Ltd. All rights reserved. Keywords: Gerbils; Social behaviour; Sex-differences; Pairbond disruption Mongolian gerbils (Meriones unguicalatus) live socially in the dry areas of eastern Mongolia and Western Manchuria in cooperative pairs or extended family groups [5,6]. Family members are recognised through their ventral scent gland secretions [9] and these mixed-sex colonies become age structured as successive litters remain in the home burrow. Sub-adults are sexually suppressed and stable pairs are formed between the dominant male and the dominant female. Only this pair are in reproductive condition [2,4]. As protection against environmental extremes, family members co-operate to build the major feature of gerbils’ territories, a complex and extended burrow system. In cold conditions the temperature inside these burrows may be greater than 20°C higher than ambient [17]. Such burrows also have importance as storage places for food and as stra- tegically defensible locations in the event of there being a threat of predation [6]. In the course of gerbil territory formation, males defend an area, females select a male and finally both defend the territory against intruders [2]. However, as females have been observed mating with males other than their colony mate (e.g. [1,3,4]), the breeding pair is based on prolonged association [19] rather than an exclusive mating relationship. Gerbils are therefore avuncular [1], rather than classically monogamous [12]. Nonetheless, the pairbond is clearly very important for effective territorial functioning. Males play the major role in patrolling and scent marking territorial boundaries [2,4] whilst females are active in food hoarding [13] and nest building [18]. Importantly, both sexes play a positive role in the care and development of the young [7,8] and when the situation demands, defence against territorial intrusion [2,16]. Preliminary studies have shown that the disruption of these pairbonds has significant effects on subsequent social behaviour [10,11,14,15]. This may be expected in view of the importance of the pairbond for continued reproductive success and survival. The effects were not the same in both sexes, however. Pairbond disruption in females induces freezing in response to social advances and reduces the level of the reciprocation of social contact. By contrast, whilst pairbond disrupted males do respond to social advances they initiate fewer social contacts per se and show reduced levels of social investigation compared to pairbond maintained controls. Males previously housed in same-sex pairs or single-sex groups do not show these effects and they are not altered by housing with a new female, leading to the conclusion that they are due to the breaking of a bond with a specific individual [11]. As the sex Neuroscience and Biobehavioral Reviews 23 (1998) 273–277 PERGAMON NEUROSCIENCE AND BIOBEHAVIORAL REVIEWS NBR 330 0149-7634/99/$ - see front matter  1998 Elsevier Science Ltd. All rights reserved. PII: S0149-7634(98)00028-1 * Corresponding author.