Ontogeny and 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，但令人惊讶的是，人们对共生关系的个体发生和宿主内虫黄藻种群的人口统计学知之甚少。本项目将研究产生虫黄藻藻幼虫的柳珊瑚的共生动力学，从最初的虫黄藻吸收到宿主成年群体和宿主种群。共生群落的遗传结构数据和实地研究将用于阐明虫黄藻种群在宿主内建立和维持的机制。将对柳珊瑚宿主内部和宿主之间虫黄藻的多样性进行研究，以确定是否存在特定于特定生境或特定宿主物种的分类群。这将确定共生体宿主特异性的水平。分子技术（DNA指纹图谱，微卫星多态性位点和小亚基核糖体基因的限制性片段长度多态性）将用于表征藻黄菌在planulae初始定植中的基因型。在单个寄主群体内以及寄主群体和物种内部和之间的虫黄菌种群变异也将以这种方式表征。在许多柳珊瑚种中，多个虫黄藻分类群启动共生，而在成虫共生中只有一个优势分类群存在。本文将对柳金花丛、假丛金花、假柳金花和灰柳金花的偶氮黄藻定殖进行原位和实验室控制，以阐明这些关联在寄主发育过程中发生变化的机制。成虫黄藻种群也将被表征，以确定定殖藻种群的多样性，是否可以诱导黄藻种群的变化，以及特定寄主内的黄藻是否反映寄主-藻的特异性，黄藻之间的环境选择或仅仅是随机的，建立效应。了解虫黄藻种群的动态变化对研究虫黄藻的共生关系以及了解虫黄藻对环境变化的响应具有重要意义。现在人们认识到虫黄藻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，那么功能和生理特征的变化可能反映了寄主藻类群落结构的变化。理解这些过程对于理解共生关系至关重要。例如，对温度和光线等条件的生理适应实际上可能是由藻类共生体的人口统计学调节的。在这种情况下，检查共生关系的每个组成部分，考虑珊瑚和藻类的种群动态和生态反应，以了解和保护珊瑚礁生态系统将是至关重要的。然而，第一步是量化这种多样性，并说明这种多样性是如何建立的。

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, but surprisingly little is known about the ontogeny of the symbiosis and the demographics of zooxanthellae populations within their hosts. This project will examine the dynamics of the symbiosis in gorgonian corals that produce azooxanthellate planula larvae, from initial uptake of zooxanthellae through to the host adult colony and host population. Data on genetic structure of symbiont communities and in situ field studies will be used to elucidate the mechanisms by which zooxanthella populations within a host are established and maintained. Diversity of zooxanthellae within and between gorgonian hosts will be examined to establish whether there are taxa specific to given habitats or given host species. This will identify the level of Symbiodinium-host specificity.Molecular techniques (DNA fingerprinting, microsatellite polymorphic loci and restriction fragment length polymorphism in small subunit ribosomal genes) will be used to characterize algal genotypes in the initial zooxanthella colonization of planulae. Variation in zooxanthella populations within single host colonies and within and among host populations and species will also be characterized in this manner. In many gorgonian species multiple zooxanthella taxa initiate the symbiosis while only one dominant taxon is present in the adult symbiosis. Both in situ and lab controlled colonizations of azooxanthellate planulae of the gorgonians Plexaura kuna, Pseudoplexauraporosa, Pseudopterogorgia efisabethae and Briareum asbestinum will be followed to elucidate the mechanism by which these associations change over the course of host development. The zooxanthella populations in adult gorgonians will also be characterized to determine the diversity of the colonizing algal populations, whether changes in zooxanthella populations can be induced and whether zooxanthellae within a given host reflect host-algal specificity, environmental selection among zooxanthellae or simply a stochastic, founder effect.Understanding the dynamics of zooxanthella populations has important ramifications for studying the symbiosis and understanding how the symbiosis responds to environmental changes. It is now recognized that zooxanthellae are a diverse group. If this diversity is widespread within single host colonies or if the association is in a state of continual flux, then changes in functional and physiologic traits may reflect changes in the within host algal community structure. An understanding of these processes is essential to understanding the symbiosis. For instance, physiologic adaptations to conditions such as temperature and light may in fact be mediated by the demographics of the algal symbionts. In this case it will be critical to examine each component of the symbiosis and consider the population dynamics and ecological responses of both the coral and the algae to understand and conserve reef ecosystems. The first step, however, is to quantify this diversity and address how this diversity is established.