Satterlie, R.A.*; Nolen, T.G.: The Small Number of Swim Pacemakers in Cubomedusae May Promote Biphasic Modulation of Swimming Activity

Since the earliest behavioral investigations of scyphomedusan and cubomedusan swimming, swim contractions were found to be controlled by multiple pacemaker/sensory centers that were spread around the margin of the jellyfish. Coordination of swim pacemakers was presumed to be due to a simple dominance hierarchy, in which a discharge in one pacemaker would reset all of the other pacemakers. The resultant pacemaker redundancy was examined in three previous modeling studies in which contractile activity in a piece of jellyfish containing a single rhopalium was used to construct models of multiple-pacemaker networks. In all three studies, pacemakers were connected to one another with re-setting linkages similar to those described in earlier works. We conducted a similar study on the cubomedusa Carybdea marsupialis, but our initial results are not consistent with a model in which pacemakers interact via simple resetting linkages, thus challenging the decades-old notion of how pacemakers interact in cubozoan and scyphozoan jellyfish. In our study, real electrophysiological data were compared to resetting and independent computer model networks of pacemakers. The real data fell between that of the two models suggesting that pacemakers show a degree of independence. Our models also suggest that this type of semi-independent network may allow a greater sensitivity to asymmetrical stimuli, and thus allow significant directional reponses to these stimuli.