Individual recognition and memory in lobster dominance

American lobsters, Homarus americanus, form stable dominance relationships in captivity. Size, sex and stage in the moult cycle are important determin ants for dominance. Other factors, such as recent agonistic experience play a role. This paper investigates how lobsters maintain their stable dominan ce relationships: they may recognize individuals or alternatively, recogniz e overall dominance status. We paired lobsters in two consecutive 'boxing m atches'. Results indicate that lobsters remember familiar opponents when ke pt either in isolation or in communal tanks for 24 h between their first an d second fights. Subordinates immediately backed away from familiar dominan ts, avoiding a second fight. In some animals, this memory lasted between 1- 2 weeks if pairs were kept separate between the first and second fights. Wh en paired for the second fight against unfamiliar dominant lobsters, subord inate lobsters from first fights actively fought and won the encounter. The se results suggest that lobsters are capable of 'individual recognition'. I n nature, the observed social organization of lobsters may be maintained by individual recognition of a small number of residents inhabiting separate, nearby shelters. (C) 1998 The Association for the Study of Animal Behaviou r.