Patterns of neural circuit activation and behavior during dominance hierarchy formation in freely behaving crayfish

Creation of a dominance hierarchy within a population of animals typically involves a period of agonistic activity in which winning and losing decide relative positions in the hierarchy. Among crayfish, fighting between size- matched animals leads to an abrupt change of behavior as the new subordinat e retreats and escapes from the attacks and approaches of the dominant (Iss a et al., 1999). We used high-speed videography and electrical recordings o f aquarium field potentials to monitor the release of aggressive and defens ive behavior, including the activation of neural circuits for four differen t tail-flip behaviors. We found that the sequence of tail-flip circuit exci tation traced the development of their dominance hierarchy. Offensive tail flipping, attacks, and approaches by both animals were followed by a sharp rise in the frequency of nongiant and medial giant escape tail flips and a fall in the frequency of offensive tail flips of the new subordinate. These changes suggest that sudden, coordinated changes in the excitability of a set of neural circuits in one animal produce the changes in behavior that m ark its transition to subordinate status.