CAA: Analyses of Chemical Defenses in Young Leaves of Tropical Species

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9407835 Coley In tropical rainforest, most predation on plants by herbivores occurs on young leaves. Rates of damage are 20 times higher than on mature leaves, and 70% of the lifetime damage takes place during the short period of leaf expansion. Damage is high because young leaves are tender and rich in protein. Toughness, the most effective defense, is not possible during leaf expansion. This suggests that other defenses, including secondary chemical metabolites, may be particularly important in young leaves. Theoretical considerations of sequestration, reclamation and turnover rates of compounds also suggest that young leaves should contain a diversity of chemical defenses. However, previous studies that quantified total phenolic or tannin concentrations were unable to explain variation among species in rates of herbivory. Thus a more detailed perspective of chemical defense in young leaves is needed in order fully to understand plant-herbivore interactions in the tropics. The PI proposes to examine the secondary metabolites in young leaves by isolating and identifying as many compounds as possible from each of a few species. The deterrent or toxic activity of isolated compounds will be tested using a suite of natural enemies ranging from viruses, bacteria and fungi to insects. These sophisticated chemical analyses will allow the PI to address a variety of ecological and evolutionary questions about plant-herbivore interactions, including: 1) are current theories correct in predicting a great diversity of secondary metabolites in young leaves? 2) Why does a single species have a variety of secondary metabolites? Is it an adaptive response to the occurrence of a diversity of natural enemies? 3) It has been argued that synthesis of secondary metabolites may be physiologically incompatible with another major defense of young leaves, namely rapid expansion to shorten the period of vulnerability. The data gathered in this study will shed much light on all these intriguing ecologi cal problems.