Life history adaptations of larvacean tunicates to environmental variability

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My long term goal is to determine whole-organism adaptations of cold ocean zooplankton to environmental conditions. This is important because adaptations determine key life history traits, such as age and size-at-maturity, fecundity (i.e. egg production rate), and mortality, which together determine seasonal and interannual cycles of recruitment and abundance. Life history traits are subject to intense selection pressure and rapid evolutionary change. My guiding conceptual model is the classical life history optimization model from evolutionary theory, in which key traits are subject to physiological trade-offs, many related to body size. For example, life history theory predicts that increased body size results in increased fecundity and thus increased lifetime fitness. However, increased fecundity may be prevented by trade-offs if increased body size requires increased development time resulting in increased probability of being eaten. In this proposal I outline two objectives for the next five years; (1) to determine the reproductive allocation and fecundity of cold ocean larvacean tunicates, and (2) to determine their optimal age and size-at-maturity. Reproductive allocation will be determined in various ways, including the quantity of lipids and fatty acids invested in eggs. One hypothesis is that larvaceans are highly adept clutch size manipulators, due to a novel mechanism of selection of eggs for maturation very late in the life cycle in response to food quality. How this occurs is not known. In the second objective, I will determine the optimal age and size-at-maturity of larvaceans, and test predictions from classical optimization theory and a new, temperature-based mechanistic model. In essence, I will answer the question of whether larvaceans reproduce at a fixed size, or at a fixed age. This research will contribute to moving research on marine zooplankton beyond the biogeochemical approach of the past and into a life history theoretical context. It will be of benefit to marine scientists in both the academic and government sectors, government regulators and fisheries and aquaculture.