OXIDATIVE BREAKDOWN PRODUCTS OF CATECHOLAMINES AND HYDROGEN-PEROXIDE INDUCE PARTIAL METAMORPHOSIS IN THE NUDIBRANCH PHESTILLA-SIBOGAE BERGH (GASTROPODA, OPISTHOBRANCHIA)

Veliger larvae of the aeolid nudibranch Phestilla sibogae metamorphose in response to a soluble factor from their prey coral, Porites compressa. Metamorphosis begins with destruction of the velum, a ciliated structure used for swimming and feeding. Previous investigation had shown that P. sibogae larvae exposed to certain catecholamines lost the velum, but then failed to complete any subsequent steps characteristic of natural coral-induced metamorphosis. Because catecholamines oxidize rapidly in seawater, we have re-examined morphogenic effects of catecholamines using superfusion chambers that allow periodic replacement of test solutions. We report that fresh, unoxidized catecholamines do not induce velar loss, but that this morphogenic activity develops in aged, oxidized solutions of a variety of catecholamines and other catechol compounds. Evidence is presented that this activity is attributable to hydrogen peroxide, a byproduct of catechol autoxidation. Hydrogen peroxide induces velar loss at 10(-4) M. The possible relationship of peroxide-induced velar loss to natural coral-induced metamorphosis is discussed.