Chemical Ecology of Resin Secretion in Dalechampia (Euphorbiacea): Radical Evolutionary Shifts in the Functions of Triterpenses?

植物次生化学物质介导了植物与其共生者和拮抗者之间的许多关系。这些动植物关系的数量和特殊性造就了热带地区的生物多样性。植物通常使用次生化合物来防御食草动物或作为共生动物的引诱剂。化学性质相似的化合物在相关植物中可能具有不同的功能。本研究将通过验证萜类树脂的假设来阐明植物-动物相互作用的模型系统，萜类树脂在原始物种的叶子、托叶和花苞片中起防御食草动物和/或病原体的作用，而在传粉中不起作用。萜类树脂在大多数Dalechampia物种中起赏花作用。根据这一假说，原始的花柱植物应该用树脂保护花朵和叶子不受食草动物的侵害，同时为传粉者提供一些其他的奖励，比如花粉或香味。为了验证这些想法，拟议的项目将i)通过在天然食草动物的饲养试验中使用树脂提取物来确定无腺体和有腺体物种的萜类树脂是否会阻止食草动物；Ii)通过在微生物生物分析中检测提取物，确定萜类树脂是否抑制微生物；Iii)通过调查和分析所产生的化合物来研究花树脂和营养树脂之间的化学关系；iv)观察原始无腺体的Dalechampia物种的传粉和食草性。这项研究的信息将使我们更深入地了解植物与动物相互作用的化学基础，这种相互作用是如何进化的，以及新的互惠关系是如何产生的。

Plant secondary chemicals mediate many relationships between plants and their mutualists and antagonists. The number and specificity of these plant-animal relationships generates much of the biodiversity of the tropics. Plants commonly use secondary compounds as defense against herbivores or as attractants for mutualists. Chemically similar compounds may serve different functions in related plants. The proposed research will elucidate a model system of plant-animal interactions by testing the hypothesis that terpenoid resins, which function as floral rewards for bees in most species of Dalechampia, function in the leaves, stipules, and floral bractlets of primitive species as a defense against herbivores and/or pathogens, and play no role in pollination. Primitive species of Rhopalostylis, according to the hypothesis, should defend flowers and leaves against herbivores with resin, while offering pollinators some other reward, such as pollen or fragrances. To test these ideas the proposed project will i) establish whether or not the terpenoid resins of glandless and gland-bearing species deter herbivores, by using resin extracts in feeding trials with natural herbivores; ii) establish whether or not the terpenoid resins inhibit microorganisms, by testing extracts in bioassays with microorganisms; iii) investigate the chemical relationships between the floral and vegetative resins by surveying and analyzing the compounds produced; and iv) make observations on the pollination of, and herbivory on, primitively glandless species of Dalechampia. Information from this study will give us greater insight into the chemical basis of plant-animal interactions, how such interactions evolve, and how novel mutualisms arise.