The effect of blood signals on aggressive behaviour in mice.

The study examined whether blood applied to the coat of a male opponent mouse modifies the aggressive behaviour of the attacking male mouse. Interest was also focused on whether the signal value of blood is related to the location of different bite targets, and whether such communication is visually or olfactorily mediated. The subjects used in the study were male Turku Aggressive (TA) mice of the 57th generation of selection for high levels of aggressiveness. The 72 TA males were divided into six groups matched on the times of latency to the first attack in standard dyadic aggression tests. Different groups of male TA mice were tested against opponents with blood, a red solution or nothing applied to either both flanks or the forehead. Testing was discontinued after the first attack. The results showed that blood had an inhibiting effect on aggression unrelated to the location of its application. The opponents with blood applied to their coats were attacked significantly later and the TA males sniffed such opponents significantly more. Odours associated with blood presumably serve as signalling pheromones. The biological significance of blood signals is discussed.