TWO TYPES OF ORIENTING BEHAVIOUR DURING AGONISTIC ENCOUNTERS IN THE CRAYFISH PROCAMBARUS CLARKII (DECAPODA: CAMBARIDAE)

The crayfish Procambarus clarkii (Girard, 1852) is a territorial animal. When two male individuals are paired in the same tank, a dominant and subordinate relationship is determined after several conflicts. Before the establishment of dominance order, both individuals approached each other to contact and fight. After establishment of dominance order, dominant individuals predominantly attack subordinate individuals whereas subordinate individuals respond with either a retreat or tailflip. By comparing two orienting behaviours of the dominant individuals using video analysis, we found that the chasing speed of attack was considerably faster than that of approach, and individuals exhibited a raised position during the attack. In attack, dominant crayfish extend the abdomen as they close into opponent individuals. Furthermore, dominant individuals raise their chelipeds at the joint between the carpopodite and meropodite to threaten subordinate individuals. These results provide an initial approach to understand the neural switching mechanism that crayfish perceive when becoming dominant during agonistic bouts.