欺骗传粉系统中传粉者适合度损失的实证研究

A central problem in studying the ecology and evolution of plant-pollinator mutualisms is understanding the stable persistence of plant and pollinator in deceptive and antagonistic pollination system. Currently, nearly all knowledge of benefit and cost in pollination mutualisms comes from highly specialized pollinating seed-consumer mutualisms. Particulary, the cost for this reaction is based on the cost to the plant because it is relatively easy to quantify. However, the costs to pollinators would theorectically and empirically occur if sexual deception causes pollinator to ejaculate and waste their sperm on the flower, to mate or prefer mating with flower, and if brood-site deception makes pollinator to lay the eggs on the flower and waste their offsprings. Thus, we refer the plant-pollinator deceptive relationship with pollinator fitness suffering as pollinator offspring parasite deceptive pollination system. Comparing with complex methods to identify the sperms on the flower, the eggs laid by female pollinators on the flower of brood-site deception plant can be easily and clearly identified. Moreover, it is nearly no posible to quantify the sperms wasted in the flower and to quantify the lose of mating opportunity of male pollinators in sexual deceptive pollination system. However, the eggs laid by female pollinators on the flower of brood-site deception plant could be clearly counted, and the cost of the pollinators could be estimated directly. In this project, three species of Paphiopedilum (Orchidaceae) with brood-site deceptive pollination system are selected. Our previous studies showed that female aphidophaour hoverflies could lay one or more eggs on the flower of those slipper orchids. Consequently, the cost to pollinators will be different in the brood-site deceptive pollination system. If only one egg was laid on the flower, the young larva will starve to death. Then the cost to pollinator is 100%. If two or more eggs were laid on the flower, young larvae may survive by cannibalizing conspecific eggs on the same flower. If two or more eggs on the flower were laid by two or more visitation, then the male and female fitness of slipper orchids could be increased. The study of this relationship will delive new insights into the ecological maintenance of such plant-animal interaction. The aims of this project are: 1) to quantify the relationship between the male and female fitness of slipper orchids and the number of pollinators visits to a flower or the number of eggs on the flower; 2) to quantify the relationship between the cost of the polliantor (the surviving rate of eggs on the flower) and the number of eggs on the flower; 3) to quantitatively measure the changes of floral odour and colour after pollinator visitation for exploying the mechanisms prevention instability from pollinator losing due to overexploitation of pollinators by plants.

欺骗和对抗传粉关系的进化及维持机制是研究植物与传粉者之间合作进化的核心问题。从收益的角度看，欺骗和对抗传粉关系意味着植物与传粉者合作方都有可能获得收益、没有收益、甚至损失（负收益）。植物的损失因易于确定并能定量估测而受到广泛关注，有关对抗传粉关系的进化和维持机制都是基于植物的负收益而提出。显然，针对传粉者损失的研究将有利于全面和深入认识对抗传粉关系的进化和维持。我们将传粉者损失的欺骗传粉系统称为"传粉者子代寄生的欺骗传粉系统"。本项目拟以兰科杓兰亚科兜兰属植物与食蚜蝇（传粉者）典型产卵地欺骗传粉系统为研究对象，综合野外观察和人工控制性试验确定兜兰繁殖适合度收益、食蚜蝇适合度损失以及食蚜蝇访花次数三者之间的关系；通过测定兜兰花部视觉和嗅觉信号在授粉前后的变化，并开展传粉者行为生物活性评估试验，揭示兜兰属植物控制传粉者访花频率的反馈机制；阐明兜兰属植物产卵地欺骗传粉系统生态稳定的维持策略。

欺骗和对抗传粉关系的进化及维持机制是研究植物与传粉者之间合作进化的核心问题之一。通过野外实验和分子遗传学手段量化食蚜蝇付出的代价（卵的数量和遗传质量）和紫纹兜兰的雌雄适合度收益（花粉块转移率、结籽率和果实重）之间的关系。结果发现，在单花和斑块水平，食蚜蝇付出的代价在数量和质量上均随着兰花的雌雄适合度的增加而增长，其平均代价随兰花种群的增大而减少。通过卵的母系推断估测出单个食蚜蝇传粉者的代价远远小于其终生繁殖力。这些结果共同说明，从传粉者角度来看，产卵地欺骗是一个相对稳定的系统，不支持该特化剥削关系走入进化死胡同的假说。同时，该结论也表明被子植物特化的花欺骗系统具有相当程度的进化稳定性和耐受性。.在种群水平，以传粉食蚜蝇代价和紫纹兜兰繁值适合度的数据为基础构建一个紫纹兜兰、食蚜蝇和紫纹兜兰的模拟对象蚜虫等三者在群落水平的模型。对模型进一步优化，同时将3个参与者进行各自最优适合度的分析，将已有相关参数，包括如植株密度、花的吸引力、三者死亡率和出生率等在模型上进行运算。结果显示，传粉者代价在一定程度上可以促进植物的繁殖成功和维持三者关系的稳定性，但高的传粉者代价可能会通过降低植株密度和提高吸引力的方式来维持这种欺骗性传粉关系的稳定性。.系统发育研究表明兜兰属中蝇类传粉类群的物种形成速率大于蜂类传粉系统的类群。以欧洲地熊蜂和长尾管蚜蝇分别代表兜兰属的蜂类和蝇类传粉昆虫，对兜兰属代表性种类和人工杂交后代进行视觉和嗅觉行为学实验。结果显示，不同兜兰属种类对蜂类和蝇类几乎都产生吸引，但吸引力强弱有差异。杂交产生的新性状对蜂类和蝇类的吸引力与父母亲本相比会产生变化。“传粉通道”与传粉者体积大小的匹配程度成为兜兰属植物传粉成功的一个关键制约因素。在蝇类传粉/产卵地欺骗的兜兰属物种中柱头到传粉通道内壁的距离和花粉块到传粉通道内壁的距离值均小于蜂类传粉/食源性欺骗的兜兰属植物。

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