Collaborative Research: The Evolution of Leaf Form in Viburnum (Adoxaceae)

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"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." Terrestrial plants display remarkable variation in many aspects of leaf form. Leaves serve as main sites for photosynthesis, and are thus primary custodians of plant growth and ultimately, fitness. Previous work suggests that there are optimal values for particular leaf traits in a given environment that will maximize growth, and thus predicts that certain leaf forms will evolve under certain conditions. However, evolutionary response to external pressures such as climate may be constrained, because leaves are developmentally and functionally integrated parts of the whole plant. In spite of the long-standing interest in the role of leaves in plant ecological adaptation, few studies have successfully documented consistent evolutionary shifts in leaf traits in relation to environment. This collaborative project will develop the plant lineage Viburnum (Adoxaceae), a widespread group of approximately 168 species of woody shrubs and trees, as a model system for investigations into the ecology and evolution of leaf form. Viburnum is ideally suited for this problem as it exhibits a remarkable diversity of leaf shapes and sizes, and much is already known regarding evolutionary relationships within the group. The interdisciplinary PI team will collect physiological data from two common gardens, anatomical and environmental data from herbarium collections, and molecular sequence data for phylogenetic analyses to produce a unique, whole-lineage perspective on leaf evolution that is simultaneously detailed and broad. They will directly test several hypotheses regarding stem and leaf co-evolution, the decoupling of certain aspects of leaf water use from photosynthetic capacity, and the evolution of particular leaf traits in response to environmental conditions. One prediction is that considerable leaf shape diversity has evolved within a relatively narrow climate space, suggesting that other factors have historically been more important in shaping the evolutionary trajectory of leaf structure and function. Results from this work may be directly relevant to predicting plant response to rapid climate change. This work will also result in the development of new online community-wide teaching and research resources, such as a large leaf collection for anatomical study. In conjunction with the Peabody Museum of Natural History and public school teachers from the Providence, RI area, the PI's will also develop two 'leaf diversity' education modules targeted for elementary and high school levels in the New Haven and Providence school districts.