Sterol Limitation of Zooplankton Growth: Roles in Nutrition and Membrane Biology

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This study will provide a first look at cholesterol as a limiting nutrient and plasma membrane constituent for zooplankton. Physical and biotic conditions for which dietary sterols become limiting will be identified, and the coupling between dietary and membrane-specific requirements for sterol will be defined. The central hypotheses to be tested include: 1) Exogenous sterols are limiting factors for copepod growth. 2) Cholesterol supplementation of the diet affects growth rates but not cholesterol contents in plasma membranes (i.e., an optimal level of cholesterol is maintained despite variability in diet). 3) Cholesterol contents of membranes and dietary limitation of cholesterol are affected by growth temperature. The foci of the proposed research will encompass a range of levels of biological organization from organismal. to biochemical processes. Zooplankton (including eurythermal and other, ecologically important, species) will be raised on diets using different a) algal species and b) levels of supplemented cholesterol. Egg production rates, egg hatch rates, and/or growth rates will be determined under different biotic and physical conditions. Cholesterol will be delivered in gelatin-acacia microcapsules and ingestion rates monitored by particle counter. Plasma membranes will be prepared using density-gradient centrifugation and cholesterol contents analyzed. Much of the research proposed is especially well-suited for undergraduate student involvement. Students will gain conceptual and specific knowledge of zooplankton and temperature biology as well as fundamental mechanisms in physiology/biochemistry. In addition, students will learn valuable laboratory techniques from hands-on experience with a variety of methodologies. These experiences will be further enriched by interactions with researchers at a marine laboratory.