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.