Dominance hierarchies and status recognition in the crayfish, Procambarus acutus acutus.

In the eastern white river crayfish, Procambarus acutus acutus, the processes that act during hierarchy formation were explored by analyzing the behavior of 23 symmetric pairs of form I males. The experimental design comprised three subsequent phases: isolation, familiarization, and experimental phases. In the latter, pairs were formed of (i) unfamiliar opponents having different status, (ii, iii) unfamiliar opponents having the same status, either two alphas or two betas, and (iv) familiar opponents. The first result was that P. a. acutus is capable of establishing stable dominance hierarchies. Secondly, behavioral differences between the winners and the losers, a fast assessment of status, and self-reinforcing effects of recent experience were demonstrated. Thirdly, P. a. acutus was found to recognize the status of its rival but not its individual identity. In fact, even if paired with unfamiliar opponents, previous winners and losers behaved as in the preceding days. Conversely, both frequency and intensity of fighting increased when individuals of the same rank were opposed. These phenomena might be a consequence of "winning and losing effects". However, the increased readiness of former betas to attack contradicts the loser effect and validates the hypothesis of status recognition.