INDUCTION OF METAMORPHOSIS IN LARVAE OF A SPONGE

Elevated exogenous KCl and CsCl are effective artificial metamorphic t riggers for many, but not all, invertebrate larvae. Neither taxonomic nor functional patterns in their effectiveness, however, are apparent. In our experiments, elevated exogenous KCI promoted metamorphosis of larvae of the demosponge Aplysilla sp., but only when applied simultan eously with a biofilmed artificial substratum. Although the presence o f this artificial substratum alone significantly enhanced settlement o ver seawater controls, its effectiveness was further augmented signifi cantly in the presence of elevated KCl, indicating a synergistic inter action. Exposure of larvae to a 2-min pulse of 30 mM KCl promoted meta morphosis as effectively as continuous exposure to 30 mM KCl. Moreover , 30 mM CsCl proved an effective trigger of metamorphosis both in the absence and presence of a biofilmed substratum. As with KCl, the CsCl data indicate the presence of a synergistic interaction between CsCl a nd the biofilmed substratum. This report provides preliminary insights into the induction of settlement and metamorphosis of sponges, metazo ans which lack established sensory and neuronal elements, and it permi ts comparison with responses of eumetazoans.