The role of the legs in the lateral giant fibre escape of the crayfish Cherax destructor (Crustacea: Decapoda: Astacura)

Abstract

AbstractIt is known that leg positioning is important for reducing drag during escape mediated by the medial giant (MG) axon of the crayfish (Cooke and Macmillian, '85). This report examines the question of whether the legs also have a role in escape mediated by the lateral giant (LG) neuron. The trajectory and the dynamics of the lateral giant (LG) escape behaviour of the crayfish Cherax destructor were analyzed using high speed cinematographic techniques. The LG escape flip was found to be stereotyped for each particular animal but rested animals produce their own characteristic trajectories. We tested to see if denervation of the legs would alter the escape trajectory. Interference with the articulating membrane at the base of the legs alters escape performance and a new set of displacement curves characteristic of each animal is produced. This is the outcome whether or not the nerves are severed. Electrophysiological recordings confirmed earlier latency measurements (Cooke, '85) and indicate that the efferent signals to the legs evoked by LG activation arrive too late to position them to influence the escape trajectory. We suggest that operations on the articulating membrane produce their effects by altering the starting position of the legs. We provide some preliminary evidence that supports this hypothesis.