THE ROLE OF SUBSTRATE ODORS IN MAINTAINING SOCIAL TOLERANCE BETWEEN MALE HOUSE MICE, MUS-MUSCULUS-DOMESTICUS

Odours deposited on home substrate by male house mice were manipulated experimentally to test whether cues deposited by subordinates help to maintain social tolerance between familiar mice living in the same social group. Groups of three unrelated wild-stock males were housed together from weaning until adult. Mice were then housed individually on substrate soiled by fellow group members, but allowed to interact with group members for 1 h/day over a 5-day period; this simulated the situation in free-living populations where mice may meet only occasionally but are in continuous contact with shared group substrate odours. In control groups, substrate from the individual cages of all three group members was mixed together daily to maintain their contact with fresh group odour cues. In experimental groups, substrate from one of the two subordinates in each triad was not added to the cages of fellow group members after day 2 to simulate his dispersal from their group; this Dispersed subordinate continued to receive fresh cues from fellow group members each day. Both the dominant male and Resident subordinate showed significantly increased aggression towards the Dispersed subordinate but not towards the other member of their group after the Dispersed male stopped contributing fresh cues to their home cage substrate. Results thus suggest that subordinate male substrate odours are important cues for maintaining the individual recognition of tolerated group members by both dominant and subordinate males. The adaptive significance of the characteristically restricted pattern of substrate marking by subordinate male mice is discussed. © 1993 The Association for the Study of Animal Behaviour. All rights reserved.