Abstract
Chemical cues from conspecifics are believed to induce settlement of cypris larvae in barnacles, and a settlement-inducing protein complex, SIPC, is thought to be one of the key substances for gregarious settlement in Balanus amphitrite. In the present study, we examined effects of adult extracts including SIPC and nature of substrata on larval settlement in B. amphitrite and Megabalanus rosa by multiwell plate assay and membrane filter assay. Especially in M. rosa, settlement rates of the cypris larvae after larval culture in the presence of antibiotics are higher than those in the absence of antibiotics. Larval settlement in both species was induced by conspecific adult extracts in both assays using multiwell plates and mixed cellulose ester type membrane filters (CE). However, no cypris larvae settled on cellulose acetate type membrane filters (CA), which are inactive for protein adsorption. The results of assays using five different types of membrane filter showed that capacity for protein adsorption in substrata seems to affect larval settlement. On the other hand, the settlement pattern of M. rosa cyprids in a choice assay using CE was different from that of B. amphitrite; B. amphitrite cyprids settled exclusively on the adult extract-adsorbed region, while M. rosa cyprids settled on the unadsorbed region as well as the adsorbed region. These results indicate that settlement-inducing proteins and nature of substrata are important factors in larval settlement of barnacles, and that settlement patterns are species-specific.
