MORPHOGEN-BASED CHEMICAL FLYPAPER FOR AGARICIA-HUMILIS CORAL LARVAE

Larvae of the scleractinian coral Agaricia humilis settle and metamorp hose in response to chemosensory recognition of a morphogen on the sur faces of Hydrolithon boergesenii and certain other crustose coralline red algae. The requirement of the larva for this inducer apparently he lps to determine the spatial pattern of recruitment in the natural env ironment. Previous research showed that the inducer is associated with the insoluble cell wall fraction of the recruiting algae or their mic robial epibionts, and that a soluble but unstable fragment of the indu cing molecule can be liberated by limited hydrolysis, either with alka li or with enzymes specific for cell wall polysaccharides. We now show that the parent morphogen can be solubilized by gentle decalcificatio n of the algal cell walls with the chelators EGTA or EDTA, suggesting that the morphogen may be a component of the calcified recruiting alga itself, rather than a product of any noncalcified microbial epibionts . The solubilized inducer is subsequently purified by hydrophobic-inte raction and DEAE chromatography. The purified, amphipathic morphogen r etains activity when tightly bound to beads of a hydrophobic-interacti on chromatography resin, and this activity (tested with laboratory-rea red larvae) is identical in the ocean and the laboratory. We have atta ched the purified, resin-bound inducer to surfaces coated with a silic one adhesive and thus produced a potent artificial recruiting substrat um-i.e., a morphogen-based chemical ''flypaper'' for A. humilis larvae . This material should prove useful in resolving the role of chemosens ory recognition of morphogens in the control of substratum-specific se ttlement, metamorphosis, and recruitment and in the maintenance of spe cies isolation mechanisms in the natural environment.