The effects of social experience on the behavioral response to unexpected touch in crayfish

Crayfish fight and form a dominance hierarchy characterized by a pattern of repeated agonistic interactions between animals with a consistent outcome of winner and loser. Once a dominance hierarchy is established, dominant animals display an elevated posture with both claws held laterally and forward, whereas subordinate animals display a more prone posture with both claws extended forward and down. Dominant animals behave aggressively towards the subordinate opponent, often approaching and attacking, whereas subordinate animals behave submissively by tailflipping and retreating. To evaluate whether the differences in social behavior are accompanied by differences in responses to non-social stimuli, we exposed socially naïve and experienced crayfish (Procambarus clarkii) to an unexpected touch in different social conditions. Socially naïve animals turned to confront the source of a unilateral touch with raised claws and elevated posture. Dominant animals also turned to face the stimulus source with raised claws and elevated posture, both when tested alone and in the presence of a subordinate opponent. Subordinate animals displayed this orienting response only while separated from their dominant partners. When paired with their dominant partners, subordinates avoided the stimulus source by walking rapidly forwards or backwards. When the subordinate animals were later tested again, first while semi-separated from the dominant and later while fully separated, they displayed a mixed pattern of avoidance and orienting responses. These results indicate that the behavioral responses of subordinate crayfish to touch depend on their social status, their current social conditions and their recent social history.