Sensory aspects of the control of orientation to prey by the waterstrider, Gerris remigis

Summary

• 1. Sensory aspects of the control of orientation to surface ripples have been examined in the waterstrider. The angular component of the motor response of tethered animals is highly correlated with the angular deviation of a target from the longitudinal body axis (Fig. 1).

• 2. Amputation of three unilateral legs just proximal to the tibio-tarsal joint blocks normal orientation. Most turns by these preparations are directed toward the intact side irrespective of target position (Fig. 3). Amputations at more distal points on the legs have no observable effect (Fig. 2).

• 3. Orientation does not depend on a full complement of receptors since responses normally correlated with target deviation do occur when the target is ipsilateral to the intact receptors of a unilaterally amputated preparation (negative target deviations, Fig. 3).

• 4. A series of ablation experiments suggests that the system may function by determining the receptor nearest the source of ripples since a number of fairly accurate predictions can be made by assuming this is the case (Figs. 5, 6, 7, 9).

• 5. Each receptor has a negative influence on the torque elicited by an ipsilateral and more posterior receptor.