SGER: Development of Radioisotope Methods to Detect Costs ofInducible Defenses and Associated Translocation Shifts

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Biotic interactions of sessile colonial invertebrates are often mediated by inducible structures that are locally deployed on the colony. In no other group of animals is there likely to be such a tight relationship between the function of ecological interaction and underlying physiological constraints. Colonies of the marine bryozoan, Membranipora membranacea, specifically change morphology with changes in the biotic environment: spines are induced by predators, and stolons by some conspecifics. Previous work has shown that the spines exact a fitness cost and this project will test the hypothesis that the mechanism underlying the cost is disruption of colony-wide translocation and metabolic patterns. Although inducible defenses are common in marine, terrestrial, and freshwater organisms, and costs have been frequently demonstrated, no studies have elucidated mechanisms underlying costs of defense. The current hypothesis of this project is based on the concept of a simple source-sink model controlling the basic process of translocation in bryozoan colonies and linking physiological function with ecological performance. This project will attempt to develop radioisotope methods using 14Carbon and 35Sulfur to test the hypothesis.