Conspecific Urine Markings in Male Rats (Rattus Norvegicus) Selected for Relative Aggressiveness.

Male laboratory rats were selected for relative aggressiveness and tested individually and in pairs to examine conspecific marking in relation to object marking. Urine deposited on the other animal and in the environment was rendered visible and quantifiable with sodium fluorescein and filter paper, respectively. Moderately aggressive males were used in Experiment 1, and despite individual differences in both forms of marking, there was a high positive correlation between quantity of marks in the environment and on a conspecific. In Experiment 2, aggressive males marked the environment and their nonaggressive partners more than vice versa. Nonaggressive males were paired successfully with an aggressive and another nonaggressive male in Experiment 3 to examine the crawl-over response, the behavior used by rats to deposit scents on another rat. Nonaggressive males deposited more urine with each crawl over an aggressive than over a nonaggressive male, but they crawled over the nonaggressive male more often than the aggressive male. These data are interpreted as suggesting that conspecific marking is modified by limitations imposed on the behavior by the social relation of the interacting animals.