Urine odours and marking patterns in territorial laboratory mice (Mus musculus )

Responses of subordinate male mice in an open field, half of which was spotted with water and half with urine collected from other males were analysed. Test mice avoided the urine of dominant mice which held territories in a "free range" room, but not of caged dominants or of singly housed males. They spent more time in the urine half of the open field when it was spotted with the urine of free-range subordinates. Locomotor activity was depressed in the presence of caged subordinate urine. The urine marking patterns of the different categories of males were investigated in a separate experiment. Subordinate males tend to deposit their urine in relatively few large pools mainly at the edge of a test arena, whilst dominant and singly-housed animals produce large numbers of tiny spots. Dominant animals urine-mark evenly over the entire area, whereas singly housed animals mark more intensely at the periphery than at the centre. It is concluded that only territorial males produce in their urine a factor that deters other (at least subordinate) males from investigating areas marked with it, and that they actively distribute it over a wide area.