The evolution of life histories in geminate echinoderms: a comparative approach to unscrambling the relationships among environment, egg size, and the energetics of development.

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Egg size is one of the most important and often-studied aspects of the life history of marine organisms, and is correlated with many traits including larval developmental mode, length of larval development, starvation resistance, larval form and function, size at metamorphosis, and juvenile growth and survival. Much attention has focused on the ecological factors that drive evolutionary changes in egg size, but the relationships between ecological, evolutionary, and physiological aspects of larval development have yet to be characterized. Likewise, while assumptions about the relationships between egg size and the utilization of egg energy by developing larvae are built into all major models of life history evolution in marine organisms, no study has explicitly tested the underlying assumptions of these models in a rigorous comparative framework with a well-described ecological and evolutionary context. To examine these assumptions, the principle investigator will use geminate species pairs of echinoderms separated by the closure of the Central American Seaway as a model system for understanding the evolution of egg size and its implications for a wide range of other life history correlates among marine invertebrates. Specific questions to address by the research include: (1) What are the changes in biochemical composition that are associated with evolutionary changes in egg size? (2) How do evolved differences in egg size, egg composition, and total egg energy affect the growth rates and developmental trajectories of larvae? (3) In planktotrophic species, do larger eggs contribute a higher proportion of energy to the total cost of development than smaller eggs? (4) How does egg size affect subsequent larval performance under different food regimes that mimic the contrasting natural food environments in the two oceans? The broader impacts include funding one postdoctoral researcher, two graduate students, and at least 3 undergraduates. Students will be directly involved working with samples collected in Panama, and will learn the principles of comparative biology, data acquisition and organization, and data analysis by working directly (under faculty supervision) with datasets they collect themselves. This research will be communicated to the public via a web page hosted at Clemson University and maintained by the principle investigator and will serve as the foundation for the development of a "Larval Wiki," a public web resource that can be contributed to and edited by anyone. The principle investigator hopes this Wiki will become a self-sustaining resource that will be of considerable use to the global community of larval biologists as a forum for discussing major issues, disseminating information, and sharing photographs for teaching and public presentations.