Development Of Mechanosensory Responses In Myelinated Copepods

Abstract

This thesis will examine the mechanosensory capabilities of juvenile copepods from an essential prey species in the North Atlantic food web, Calanus finmarchicus. An important underlying component of these interactions is myelination of axons associated with decreased response latencies, yet myelination has not been observed in electron micrographs of copepod nauplii. Electrophysiological recordings from juvenile copepods are presented and their analysis found that myelin is consistently present in CII and later copepodite stages (CI copepodids could not be obtained for recording). Two unidirectional mechanosensory units were distinguished in all developmental stages studied using a controlled hydrodynamic stimulus, while a third slower non-mechanosensory unit was observed. Adults were found to be the most sensitive to mechanosensory stimuli, with thresholds of water displacement (not velocity, as reported in other copepods) of less than a nanometer. While copepodids were less sensitive, much longer antenna:prosome ratios were observed in CII copepodids.