Chemical Defenses in a Toxic Dinoflagellate: Mechanisms and Constraints

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Intellectual merit: Species of the dinoflagellate genus Alexandrium occur around the globe, and some species, because of their toxin production, have been hypothesized to be keystone species. Alexandrium produces chemical compounds that appear to target different consumers. Neurotoxins such as PST target metazoan grazers. In preliminary experiments in their laboratory, the investigators also verified the presence of reactive oxygen species that target, at a minimum, protistan grazers. Such compounds reduce grazer fitness, and, at least in the case of PST, have been shown to have profound evolutionary effects on grazers. Grazer adaptation, in turn, can affect Alexandrium population dynamics. A common assumption is that production of toxic compounds in phytoplankton represents an adaptive defense. However, unequivocal experimental evidence in support of this hypothesis is scarce. This project will be a rigorous experimental test of the chemical defense hypothesis. The project's investigators will invwestigate a series of experimentally falsifiable hypotheses with both metazoan and protistan grazers challenged with Alexandrium. This project will provide novel understanding of, and insight into, the factors that determine grazer-induced toxin production, the relationship between degree of chemical defense and susceptibility to grazing, and the costs and tradeoffs of the purported mechanisms of chemical defense in Alexandrium. Verification or refutation of the chemical defense hypothesis is essential to conceptual models of the formation, control and persistence of toxic algal blooms, and chemically-mediated predator-prey interactions. Broader impact: There is an immediate and urgent need to improve the public's awareness of publicly funded science and the world's oceans. To help fill this need, the investigators will work with professional educators to translate results from this study into prepared curricular materials that meet national science standards. They will make the results of this and related studies available to secondary educators through their website "Predators and toxic prey," where educators will find materials that can be incorporated into high school curricula. The investigators also will present the website contents at workshops specifically targeted at secondary school educators, and at meetings of professional educators. The lead investigator and his team will continue to extend the results of research to lay audiences, as well, through the website, lay articles and the "Aquakids" TV series. This project will train one Ph.D. student and one or two undergraduates. In addition, the proposed work will engage graduate and undergraduate students in several areas of research from physiology to ecological and evolutionary processes. In the process, these students will effectively be studying the emergent properties that lead to adaptability and apply such perspectives to oceanography.