Scent exposure influences competitive behaviour in lab mice

Lacey, J.C. Beynon, R.J. & Hurst, J.L. (2007) The importance of exposure to other male scents in determining competitive behaviour among inbred male mice. Applied Animal Behaviour Science 104, 130-142 [PDF]

Inbred mouse strains are homozygous at almost all loci, with individuals of the same strain expressing the same genetically determined scents that would normally provide individuals with their own unique scent. As laboratory mice are normally housed with others of the same strain in a simple and constant environment, this will compound the ability of inbred mice to link social status with individual identity within their social group. Further, mice may be exposed accidentally to the scents of others during routine maintenance, or during experiments, which may influence their competitive relationships. We investigated the effect of repeated exposure to soiled bedding from males of either the same or different strain on competitive urine counter-marking and investigation and on aggressive behaviour within same-strain pairs of BALB/c and C57BL/6 males. Males pre-exposed to different strain scents in the home cage had more defined social relationships, in that dominant males were more aggressive while subordinate males suppressed counter-marking near other male urine. Exposure to male urine from the same or different strain outside the home cage stimulated increased aggression when males returned home, an effect that was exacerbated by different strain scents in the home cage. The duration of urine investigation varied according to both strain and experience of home cage scents. Results demonstrate the importance of scent experience in determining competitive behaviour among male mice. To protect welfare, we recommend that males are not exposed to male urine when temporarily removed from their social groups and that care is taken to avoid contamination of home cages with different strain scents, for example, by cleaning cages thoroughly and ensuring that soiled substrate cannot fall into other cages.