Meeting Abstract

10.2  Jan. 4  The elementary (pre-)nervous system reconsidered: new evidence from poriferans NICKEL, M; Stuttgart University, Germany michael.nickel@bio.uni-stuttgart.de

In 1919 Parker presented basic ideas on the elementary nervous system. He assumed it became manifest due to the evolutionary pressure to coordinate independent effectors. The concepts behind his theory continued to hold with little changes over time. In 1956 Pantin stressed the evolutionary importance of coordinating cell networks. Passano (1963) postulated pacemaker cells to be the nucleous of nervous system evolution. Mackie (1990) reviewed the topic. All concluded that the cnidarian nervous system is the primary nervous system. However, Mackie pointed out that more work on sponges is needed. The recent (re-)postulation of the paraphyly of the Porifera consequently means that a sponge like animal would be within the ancestral line of all metazoans. The question arises, if the first modules of the rather complex elements of later nervous systems evolved in such a sponge like archimetazoon. Our work on the coordination systems in poriferans, which particularly focused on neurosecretory substances, is summarized. Monitoring contractile response of our model organism Tethya wilhelma, we recorded and analyzed a variety of specific responses to a variety of neuromodulating substances. Our results as well as recent sponge EST sequencing projects clearly show the presence of complex networks of regulatory circuits within a system of effectors, signal conductors and pacemakers. All criteria for the elementary nervous system given by former investigators are met. Even if no true neurons are present in poriferans, the physiological functionality and complexity can only be explained by a well-defined pre-neuronal system. Consequently, the evolutionary origin of the nervous system dates back to the basal Metazoa, most likely extinct archimetazoans.