Natural and Artificial Induction of Metamorphosis of Phragmatopoma Lapidosa Californica (Polychaeta: Sabellariidae), with a Critical Look at the Effects of Bioactive Compounds on Marine Invertebrate Larvae
Abstract:Recent studies of the effects of bioactive compounds on the settlement and metamorphosis of marine invertebrate larvae prompted the present study of the larval responses of the tube building polychaete Phragmatopoma lapidosa californica to these compounds. Choline, succinylcholine and serotonin induced variable levels of abnormal metamorphosis of P. I. californica. Larvae did not respond to γ-aminobutyric acid (GABA). Both D- and L-3,4-dihydroxyphenylalanine (DOPA) induced 10-30% normal metamorphosis, but larvae did not respond to dopamine, norepinephrine or epinephrine. L-DOPA underwent rapid oxidation in seawater, and solutions left standing for longer than 2 h lost the capacity to induce metamorphosis. Whereas metamorphosis in response to palmitoleic acid (a naturally occurring inducer) was rapid, larval response to L-DOPA was delayed for several hours, suggesting that L-DOPA does not act on an external epithelial chemoreceptor. Four compounds that alter the transport of ions across membranes were tested and three of these, tetraethylammonium (TEA), sulfonyl isothiocyanostilbene (SITS) and picrotoxin, had no apparent effect on larvae. Ouabain at 10–5 M induced abnormal metamorphosis in a high percentage of larvae exposed to sand coated with palmitoleic acid, but had no effect on larvae exposed to control sand. Ouabain also had no effect at lower concentrations, and was toxic at higher concentrations. Three compounds that alter intracellular concentrations of cyclic AMP (cAMP) in some cell systems were tested and two of these, dibutyryl cAMP (db-cAMP) and cholera toxin, had no effect on larvae of P. I. californica. Isobutylmethylxanthine (IBMX) induced a high percentage of normal metamorphosis at 10–5–10–4 M.
Available evidence does not support the hypotheses that (1) natural inducers of marine invertebrate larval settlement and metamorphosis are structurally related to neurotransmitters, and (2) metamorphic activation among different invertebrate larvae occurs by one general pathway. The compounds used in this and previous studies frequently have multiple or variable effects on different cell lines or tissues. Assays of the effects of bioactive compounds on whole invertebrate larvae are not specific, neither in terms of the cells that are affected nor the responses that are observed. Therefore, it is presently untenable to propose detailed molecular pathways controlling the activation of invertebrate larval settlement and metamorphosis based on the responses of whole larvae to these compounds.
Document Type: Research Article
Publication date: March 1, 1990
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