Prolonged exposure to social odours alters subsequent social interactions in crayfish (Orconectes rusticus)

Chemical signals in aquatic systems are used to communicate social status and consequently alter aggressive behaviour. In addition, they may also function to influence the status roles of potential opponents or in part to predetermine the outcome of agonistic interactions between opponents. Here we examined whether exposure to social odours, in the absence of other sensory contact with a 'sender', alters subsequent agonistic behaviour in crayfish. Odour-receiver crayfish were exposed to one of four different odours from a 'sender' crayfish: odours from dominant (winner), subordinate (loser), or naive crayfish, or water from a tank that did not contain a crayfish (no social odour). 'Receiver' crayfish were exposed to one of the aforementioned odours on five consecutive days. After this extended exposure, the 'receiver' crayfish was allowed to interact with an effect-evaluator crayfish that had been isolated during the 5-day exposure period. 'Receiver' crayfish that were exposed to dominant (winner) odours behaved analogous to a subordinate role in that these animals lost the majority of their fights, but they also fought more intensely compared to the other treatments. Conversely, when crayfish were exposed to subordinate (loser) odours, their agonistic interactions were less intense and they subsequently won more encounters compared to the other treatments. These results may suggest that the receivers of the dominant odours had exhausted their chemical signal reserves by responding to the signal and therefore were obliged to increase their levels of visual/tactile responses. Because their chemical reserves were no longer sufficient to reinforce the visual displays corresponding to increased fight intensity, these animals tended to lose fights. In contrast, the receivers of the subordinate odours probably had sufficient chemical reserves to communicate chemically during agonistic encounters, and consequently, won more fights.