Dynamics of cnidarian-algal symbioses

共生体属刺胞动物和鞭毛动物之间的共生在海洋环境中广泛存在。它们对造礁珊瑚和珊瑚礁营养循环的重要性有很好的记录，这些共生体的丧失（称为珊瑚白化）可能导致珊瑚礁退化和珊瑚死亡。越来越多的研究表明，这些共生体具有遗传多样性，对环境扰动的反应也各不相同。比较多个寄主分类群的共生多样性，确定共生对环境扰动的反应弹性，对于理解寄主和共生分布模式以及确定维持共生的关键过程至关重要。本项目的目的是研究共生菌的多样性是如何建立的，以及控制共生菌不同分类群分布的过程。这项工作将识别和比较以宿主-共生体特异性为特征的共生体与随环境条件变化的共生体。分子技术（微卫星多态位点、叶绿体23S rDNA长度变异和核糖体内部转录间隔区序列分析）将用于表征初始共生体定殖planulae中的共生多样性，以及单个寄主菌落内、寄主种群和物种内部和之间的共生补体多样性。具体地说，共生菌的“基线”多样性将通过在一系列栖息地上对每个寄主物种进行种群规模调查，以及评估寄主之间和不同环境下共生群落变化的方式来确定。来自近亲宿主的共生体的系统发育比较将测试共种形成，种群遗传分析将检查共生体种群之间的连通性。然后，将进行一系列操作实验，检查维持基线多样性调查中观察到的变化（或缺乏变化）的过程，以测试宿主基因型与环境（GxE）在确定成年宿主中共生体补体方面的重要性，并表征共生体-宿主伙伴关系的保真度（即共生体的特异性与灵活性）。定量实时PCR将用于量化不同共生体类群在宿主体内随时间的丰度。这些数据将有助于确定共生体种群的变化是否可以被诱导，以及特定宿主内的共生体是否反映了宿主-共生体的特异性、共生体之间的环境选择或随机的奠基者效应。了解共生生物的动态对于了解共生生物如何响应环境变化以及珊瑚礁分类群对气候变化的短期和长期响应具有重要意义。共生菌是一个多样化的群体，如果这种多样性在单个寄主群体中广泛存在，或者如果这种关联处于持续的流动状态，那么寄主藻类群落结构的变化就会引起寄主-共生系统功能和生理特性的变化。另外，具有固定的共生体补体的寄主类群对不断变化的环境条件的适应能力较差。更广泛的影响：这项工作将培养至少2-3名研究生和至少8名本科生。通过这个项目，这些学生将有机会在实验室和实地环境中参与研究，学习一系列分子和藻类培养技术。基于该提案的项目也将在实地课程中介绍，使学生小组能够根据该项目设计和开展实地研究。布法罗大学广泛的文化收藏是全世界研究人员可用的重要资源。这笔资金将使这些藏品得以维护和加强。

Symbioses between cnidarians and dinoflagellates in the genus Symbiodinium are widespread in the marine environment. Their importance to reef-building corals and reef nutrient cycles is well documented and loss of these symbionts (termed coral bleaching) can lead to reef degradation and coral death. A growing body of research shows that these symbionts are genetically diverse and vary in their response to environmental perturbations. A comparison of symbiont diversity across multiple host taxa and a determination of how flexible symbioses are in response to environmental perturbation are essential to understanding host and symbiont distribution patterns and to identifying the processes critical to maintaining a viable symbiosis. The objective of this project is to examine how Symbiodinium diversity is established and the processes that control the distribution of different taxa of Symbiodinium. This work will identify and compare symbioses characterized by host-symbiont specificity with symbioses that change with environmental conditions. Molecular techniques (microsatellite polymorphic loci, length variation in chloroplast 23S rDNA and sequence analysis of nuclear ribosomal internal transcribed spacer regions) will be used to characterize Symbiodinium diversity in the initial symbionts colonizing planulae as well as diversity of the symbiont complement within single host colonies and within and among host populations and species. Specifically, the "baseline" diversity of Symbiodinium will be determined through population scale surveys of each host species over a range of habitats and the manner in which the symbiont community varies among hosts and across environments assessed. Phylogenetic comparisons of symbionts from closely related hosts will test for co-speciation and population genetic analyses will examine connectivity between Symbiodinium populations. A series of manipulative experiments examining the processes maintaining the variation (or lack there of) observed in the baseline diversity surveys will then be conducted to test the importance of host genotype vs. environment (GxE) in determining the complement of symbiont in the adult host and to characterize the fidelity of symbiont-host partnerships (i.e., specificity vs. flexibility of the symbiosis). Quantitative real-time PCR will be used to quantify the abundance of different symbiont taxa within hosts over time. These data will help to determine if changes in symbiont populations can be induced and if symbionts within a given host reflect host-symbiont specificity, environmental selection among symbionts or stochastic, founder effects. Understanding the dynamics of Symbiodinium has important ramifications for understanding how the symbiosis responds to environmental changes and thus the short and long term responses of reef taxa to climate change. Symbiodinium is a diverse group and if this diversity is widespread within single host colonies or if the association is in a state of continual flux, then changes in host algal community structure can generate changes in functional and physiologic traits of the host-symbiont system. Alternatively host taxa with fixed complements of symbionts would be less able to acclimatize to changing environmental conditions. Broader Impacts: This work will result in the training of at least 2-3 graduate students and at least 8 undergraduates. Through this project these students will have the opportunity to participate in research in both a lab and field setting, learning a range of molecular and algal culturing techniques. Projects based on this proposal will also be introduced in a field course enabling groups of students to design and carry out field studies based on this project. The extensive culture collection housed at the University at Buffalo is an important resource that is available to researchers worldwide. The funding will enable the collection to be maintained and enhanced.