Dissertation Research: Toxic algae as a model system for intransitive eco-evolutionary feedbacks promoting cooperation.

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This project will investigate how interactions among different genetic strains of the single-celled algae Prymnesium parvum control the formation of toxic algal blooms. Toxic algal blooms occur when certain algal species become highly abundant and release toxins into the water that harm wildlife or humans. Although toxic blooms have been increasing in frequency and severity, our understanding of the factors that cause such species to either become highly abundant or to die back is still very limited. Most research has focused on how environmental factors, such as water pollution, affect bloom formation, but this explanation is inadequate in many cases. In the focal species certain genetic strains do not produce toxins; this study will test the unique hypothesis that large changes in Prymnesium population abundance result from the cooperation and competition among toxic and non-toxic genetic strains. In nature, many species exhibit cooperative behavior, even when it is not in the best interest of the cooperating individuals. Results from this work are expected to yield important insights into the evolution of cooperation and identify management strategies that can be used to control harmful algal blooms. In addition, the project will involve mentoring both undergraduate and high school students, including individuals from groups that are underrepresented in the sciences. Public lectures and a weekly radio science show are also planned.Algal species that form harmful blooms produce toxins that often function allelopathically, by killing heterospecifics, decreasing interspecific competition and releasing nutrients into the water. In this way, these toxins appear to function as a 'public good' by benefiting the entire population. In Prymnesium parvum, a low-toxic 'cheater' strain has recently been isolated that has a significantly higher growth rate than toxic 'cooperator' strains both in monoculture and in mixed culture. This system offers a unique opportunity to investigate how ecological interactions may maintain cooperative allelopathy in unstructured populations. How can toxicity be maintained, if low-toxicity strains reap the benefits of toxicity while not contributing to toxin production? This question will be explored using a combination of laboratory microcosm experiments, strain culturing, and microscope observation. Specifically, mutual invasibility experiments will be used to look for intransitivity cycles between TOX+, TOX-, and a heterospecific strain in order to determine whether eco-evolutionary feedbacks lead to maintenance of toxic variation in this algal species.