Role of conspecific cues and sugars in the settlement of cyprids of the barnacle, Balanus amphitrite

Gregarious settlement in barnacle is attributed to the settlement‐inducing protein complex of cuticular glycoprotein, arthropodin. In this study, we characterized arthropodin protein complex (APC) from crude protein extracts of whole barnacle (AE), and also from soft body (SbE) and shell (ShE). The settlement of cyprids exposed to surfaces coated with different crude protein extracts and APC components was evaluated. In the natural environment, larvae are also exposed to different dissolved sugars. Therefore, the cyprids were tagged with different sugars and exposed to AE, SbE and ShE in order to elucidate their specific role in determining the way barnacle cyprids identify conspecifics. A previously undescribed 66‐kDa subunit was observed in shell and soft body APC, and a 98‐kDa subunit was observed in shell APC. Both the subunits were shown to inhibit settlement when alone but promoted settlement in combination (ShE), suggesting that these proteins interact in a coordinated manner. The crude adult extract (AE) facilitated higher settlement compared with shell or soft body extract. However, when cyprids were tagged with different sugars and exposed to the surfaces coated with different crude protein extracts, settlement response differed and was jointly determined by the type and concentration of sugars. Such interactions could play an important role in nature as larvae encounter surfaces covered with different glycoproteins and also experience different dissolved cues.