Neurotransmitters, Benthic Diatoms and Metamorphosis in a Marine Snail

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Esther M. Leise, Professor (Creator)
The University of North Carolina at Greensboro (UNCG )
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Abstract: Many marine snails have a biphasic life cycle. They may live in diverse habitats on the ocean floor as adults, but are planktonic in the larval phase where they are subject to oceanic tides and currents. The link between these two disparate life history stages is metamorphosis, a dramatic and irreversible developmental event that transforms a larva physically, physiologically and behaviorally into a juvenile, a tiny, sexually immature adult. This conversion occurs only when animals are competent, physiologically able to respond to environmental cues that are indicative of a favorable juvenile habitat. Such cues can include biological odorants as well as physical features of the juvenile ecosystem. The idea that environmental stimuli, such as the presence of conspecific adults or useful food sources, could trigger metamorphosis in marine invertebrates was first promulgated about 90 years ago (Mo1tensen 1921). Since then, the sources of metamorphic stimuli have been identified for a variety of molluscs, including some of the caenogastropods, the more evolutionarily advanced snails. Our experiments on the induction of metamorphosis in the intertidal snail, Ilyanassa obsoleta, by benthic diatoms have demonstrated that like other marine larvae, our model organism can display positive, negative or neutral responses to various diatom species. Investigations into the regulation of metamorphosis have moved in the last 30 years from morphology and ecology to include the cells and signaling molecules that are active in the underlying neural pathways. Investigations with l. obsoleta have demonstrated that two important neurotransmitters, serotonin (5-HT) and nitric oxide (NO), play opposing roles in the neural network that controls metamorphosis. A third neurotransmitter, (gamma)-aminobutyric acid (GABA), can induce metamorphosis in abalone, primitive molluscan relatives of l. obsoleta, by binding to GABAergic receptors located on epidermal projections of chemosensory neurons. Experimental evidence indicates that GABA mimicks the action of a natural algal ligand in this situation. In contrast, results of our recent experiments suggest that in I. obsoleta, GABA functions along with NO to inhibit metamorphosis. Experimental confirmation of this idea is proceeding in our laboratory. Serotonergic neurons are retained in the anterior portion of the larval brain of most marine invertebrates, including the marine snails. Serotonin triggers or promotes metamorphosis in several other molluscs, but is not a universal metamorphic inducer. In contrast, NO preserves the larval state in l. obsoleta and although comparative work is limited, NO plays similar, although not necessarily identical roles in a few related species. Thus, metamorphic actions of NO and 5-HT generally appear to be conserved, especially within related molluscan taxa. However, we speculate that interactions between different gastropod larvae and diverse arrays of biological and physical features within their native ecosystems have led to the divergent evolutionary adaptations seen in the use of GABA and its receptors.

Additional Information

In Snails: Biology, Ecology and Conservation, 1-43
Language: English
Date: 2012
Marine Biology, Marine Snails, Ilyanassa obsoleta, Metamorphosis, Benthic Diatoms, Neurotransmitters, Metamorphic Stimuli, GABA

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