Prey attack in crayfish: conditions for success and kinematics of body motion

Abstract

1. An experimentally blinded crayfish (Cherax destructor) attacks an object that briefly touches the flagellum of its second antenna. Since there is no feedback control during the attack, the entire motor command has to be preprogrammed immediately after stimulation. 2. I studied the dynamics of the attacks by video film analysis and by decomposing the motion of the body into rotation around a centre on the long axis of the body and a translation parallel to it. The time course of both rotation and translation velocities can be fitted by pulse responses of third order low pass filters. 3. It is shown that the model of Zeil et al. (1985) to describe the attacks is adequate only, when the distancedA of the point of stimulation from the base of the antenna is short. For longer distances it predicts an insufficient rotation, and a translation larger than required. The discrepancy is traced back to the fact that crayfish simultaneously translate and rotate during an attack. 4. To program a successful attack the crayfish have the option to adjust the extent of rotationaw and that of the translationav, as well as the ratio of their time constants. They fit bothaw andav todA but do not vary the time constants. 5. It is demonstrated that for the purpose of motion analysis a centre of rotation and a translation velocity component orthogonal to the body long axis cannot be derived unequivocally. One of them has to be chosen arbitrarily. 6. The peculiarities of the crayfish' attack as compared with prey catching strategies in other animals, and the limits of single frame analysis regarding conclusions about neural events are discussed.