Responses of crayfish to a reflective environment depend on dominance status

Previous work has shown that the reflection from aquarium walls can modify several aspects of crayfish behaviour, but only if the crayfish are socialized. Such socialization is known to generate a dominance hierarchy composed of dominant and subordinate animals. The present study was conducted to determine whether or not behavioural responses to reflection depend on dominance status. Procambarus clarkii (Girard, 1852) were maintained in pairs for 2 weeks to establish dominance ranks and were subsequently observed in an aquarium in which half of the walls were lined with mirrors and the other half were lined with nonreflective plastic. Dominant crayfish spent more time on the reflective side of the aquarium than on the nonreflective side, and they spent more time in reflective corners than in nonreflective corners. Dominant crayfish also turned more frequently on the reflective side and crossed the tank more frequently toward reflective walls. Such differences in behaviour were not observed for subordinate crayfish or for crayfish that had been isolated for 2 weeks. Subordinate crayfish exhibited more reverse walking on the reflective side of the aquarium than on the nonreflective side, but crayfish in the other groups did not. Thus, responses of crayfish to reflection depend on dominance status.