BISHOP, C.D.*; PECHENIK, J; HADFIELD, M.G.; Kewalo Marine Laboratories, University of Hawaii; Tufts University, Boston; Kewalo Marine Laboratories, University of Hawaii: Metamorphosis: under stimulatory or inhibitory control?

Environmentally dependent metamorphosis of marine invertebrate larvae is a dynamic process that integrates ontogeny with habitat selection. The capacity of many marine invertebrate larvae to survive and maintain metamorphic competence in the absence of environmental cues has been proposed as an adaptative convergence (Hadfield et al., 2000). Juvenile ecology is assumed to shape how selection acts on the capacity of larvae to maintain the larval state, but knowledge of this relationship is not understood in any detail. Comparative studies of metamorphosis in marine invertebrates reveal both similarities and differences in metamorphic sensory and control pathways. For the species studied to date, nitric oxide/cyclic guanosine monophosphate (NO/cGMP) signaling serves as an inhibitory mechanism to control the timing of life-history transformations. In most cases, pharmacological reduction in concentrations of NO or cGMP is sufficient to induce metamorphosis in the absence of external cues. Recent studies with the nudibranch Phestilla sibogae, a specialist predator of the coral Porites compressa, indicate that NO/cGMP signaling also inhibits metamorphosis, but with an important difference: inhibition of NO/cGMP signaling only potentiates responses to external metamorphic cues. A reduction of internal concentrations of NO or cGMP does not induce metamorphosis. We will present data on NO/cGMP signaling in a sea urchin Lytechinus pictus, the gastropods Phestilla sibgoae and Crepidula fornicata and propose that this subtle but potentially important difference in the dynamics of NO/cGMP signaling relative to metamorphic induction reflects differences in juvenile/adult habitat specificity.