Chemoreceptive responses of the polychaete Perinereis cultrifera in a Y maze to alternative bivalve host effluents

Abstract

The errant polychaete Perinereis cultrifera occurs in high densities as a non-obligatory symbiont within the mussel bed biocoenosis. It orients positively and significantly towards Mytilus galloprovincialis conditioned sea water in a Y maze. Sample groups freshly collected from mussels and immediately confronted with M. galloprovincialis effluents showed responses ranging from indifference to highly positive and significant attraction. Of a total of ca. 400 animals tested, positive responses had a statistically highly significant prevalence. Positively oriented individuals maintained on mussels for several weeks maintained their preference for the host. Positively oriented worms responded to M. galloprovincialis effluent faster than negatively oriented ones or those belonging to unoriented groups. Both the oriented and unoriented groups when tested with effluents of Crassostrea gigas - the other main component in the upper level of mussel beds showed no oriented response and generally a low level of activity. The chemotactic response to M. galloprovincialis was flexible. An initially positively oriented group transferred from mussels onto the oyster alternative host develops a significant preference for the new host over a two week period. This shift in orientation is interpreted as a non-associative response increment due to sensitization by chemical stimuli of the tactile elicited motor response upon the substrate. The ecological meaning and the adaptive value of chemical orientation and its flexibility are discussed.