Ecological, biomechanical and neurological correlates of escape behavior in calanoid copepods

by 1977- Waggett, Rebecca Jane

Predation pressure on calanoid copepods varies among the diverse habitats they occupy, selecting for copepods with different anatomical and behavioral traits. Calanoid copepods from seven families in three superfamilies from estuarine, neritic and oceanic habitats were exposed to a controlled near-field hydrodynamic stimulus and their escape reactions were recorded using high-speed videographic techniques. Myelinated axons have been found in certain species of the more recently-evolved calanoid superfamilies. Copepod representatives from these superfamilies were expected to have shorter response latencies than species from more ancestral superfamilies due to the increased conduction speed of nerve impulses in myelinated neurons. Using frame-by-frame playback and computerized motion analysis techniques, response latency, jump speed, and acceleration were measured. Kinetic performance of copepods was highly variable, with mean escape speeds ranging between 100 – 250 mm s-1 and accelerations of 49 – 230 m s-2. Minimum behavioral response latencies of 2 ms were recorded for both myelinated and nonmyelinated calanoids. The shortest mean response latency of 3.20 ± 0.20 ms was recorded for the myelinated Mesocalanus tenuicornis. There was no significant difference between the response latencies of copepods from the myelinated and nonmyelinated superfamilies. Furthermore, no relationships were found between copepod latency and size for either myelinated or non-myelinated species. Although previous research may suggest that myelin may shorten the response latencies of certain calanoid species, non-myelinated copepods are also capable of responding rapidly, within as few as 2 ms, to hydrodynamic stimuli and produce similar kinetic performance to myelinated species. 14