Reaction times and force production during escape behavior of a calanoid copepod, Undinula vulgaris

Abstract

Effective escape behavior contributes to the success of copepods in planktonic communities. The kinematics of escape were studied in tethered Undinula vulgaris (Calanoida) by analyzing the timing and magnitude of their power strokes to a precisely controlled, sudden mechanical perturbation in the surrounding water. Copepods responded with rapid swims to water velocities of 36 to 86 μm s-1. Reaction times were under 2.5 ms following stimulus onset. The time course of force exerted was complex, but reproducible from stimulus to stimulus. Multiple power strokes ('kicks') were frequently observed in response to single stimuli. Time intervals of 5 ms were observed between the end of one escape kick and the beginning of the next. U. vulgaris developed maximum forces of 40 to over 100 dynes (dyn) during a rapid swim. The behavioral reaction times and intervals between multiple responses observed in this calanoid are among the shortest reported in aquatic invertebrates.