Exploration and metamorphosis in Balanus amphitrite Darwin (Cirripedia; Thoracica) cyprids: significance of sugars and adult extract

Abstract

Earlier observations have shown that sugars in solution adsorb electrostatically through –OH groups to polar groups associated with the cypris larva temporary adhesive (CTA). Lens culinaris agglutinin (LCA)-binding sugar chains of the adult extract (AE) have been suggested to be involved in the settlement of Balanus amphitrite. In the present study experiments were carried out to assess how cypris larvae would explore and metamorphose when treated with LCA-specific sugars (i.e. d-glucose and d-mannose). The influence of d-galactose was also assessed similarly. Evaluation of sugar-treated as well as nontreated cyprids was carried out with AE-coated and non-coated multiwells containing filtered sea water (FSW). d-mannose-treated cyprids resulted in higher metamorphosis than the nontreated cyprids at 10−8 M, whereas cyprids treated with the other LCA-specific sugar (d-glucose) showed an inhibitory effect in the absence of AE. This result implies the involvement of d-mannose moieties of AE in the settlement promotion of B. amphitrite. The barnacle cyprid, while exploring some surfaces, leaves behind ‘footprints’ of temporary adhesive. In the absence of AE, sugar-treated cyprids did not deposit footprints. Concurrently, the sugar-treated cyprids deposited footprints when exposed to multiwells coated with AE. A comparison of observations between single cyprid and multiple cyprid assays showed a similar trend, thus indicating that larva–larva interaction may not play an important role, when such pretreated larvae are subjected to assays. The third antennular segment with its attachment disc is the most obvious point of contact between the cyprid and the substratum during exploration. The detection of AE, even after blockage of polar groups of CTA on the third antennular segment, suggests availability of alternate sites for pheromone reception.