Investigations of the temporary adhesive of acorn barnacle Cypris Larvae

Abstract

During its life cycle, an acorn barnacle spans multiple niches, from a free-swimming larva to a sessile adult. Settlement is permanent and therefore the individual must locate an optimal site for access to food and reproductive partners. To this end, the final larval stage, the cyprid, is well adapted for the purpose of surface exploration and selection. In order to adhere while exploring in dynamic environments, the cyprid secretes a proteinaceous temporary adhesive from the third antennular segment. This adhesive material is uncharacterised, and the descriptions of its secretory system almost half a century old. However, there is evidence that this temporary adhesive has some homology with the pheromone responsible for gregariousness in barnacles, the settlement-inducing protein complex, as both induce gregarious settlement, and they share an immunoreactive epitope(s). This work aimed to re-examine the location of the temporary adhesive glands, and associated secretion pathways, in acorn barnacles. Additionally, it aimed to characterise the temporary adhesive protein(s) using a multi-omics approach validated by expression studies, and assess the involvement of the settlement-inducing protein complex in the temporary adhesive system. Evidence is presented that the temporary adhesive gland is located in the proximal first antennular segment, and that the system is structured differently to that of stalked barnacles. The identity of the temporary adhesive protein(s) remained elusive, but a pathway to identification was developed and candidates presented. Finally, the settlement-inducing protein complex, as it exists in adult barnacles, may not be involved in temporary adhesion. Instead, a substantially different analogue is present.