The agonistic behaviour in the red swamp crayfish, Procambarus clarkii: functions of the chelae.

In crayfish literature, chelae are reported to play a role in predator avoidance, mate acquisition, aggressive interactions and feeding. Here attention is given to the function of chelae in agonistic interactions of the red swamp crayfish, Procambarus clarkii, and the results are compared with chelar patterns of relative growth. On one hand, this study confirms that chelipeds are powerful weapons in intra-specific encounters. In both sexes, the size of chelae increases allometrically with the cephalothorax length (and with age): the older the crayfish is, the larger are its chelae and the higher is its agonistic efficiency. On the other hand, the rare occurrence of threats in intra-specific encounters seems to suggest that the use of chelae for the purpose of intimidation is less developed in P. clarkii than in other crayfish. The large chelae in Form I (= reproductive) males could be advantageous in sexual/agonistic bouts with the females, as well as to fend off intruding males. However, there are obviously added costs, coming from a higher consumption of energy; in P. clarkii, as well as in other cambarids, these costs seem to be compensated by the benefits of successful copulations.