Collaborative Research: The impact of symbiont-larval interactions on species distributions across southwestern Pacific hydrothermal vents

与微生物的共生无处不在，对发育和营养等基本生物功能至关重要。因此，宿主动物的成功可能取决于其寻找微生物伴侣并与其结合的能力。为了保证这一点，一些宿主直接将它们的共生体从亲本传给后代，而从环境中获取微生物共生体对于许多义务共生动物的生存至关重要。了解自由生活的共生体种群以及寄主如何获得这些共生体是我们理解所有生态系统中生态过程的基础，但这两方面我们几乎一无所知。热液喷口生态系统为研究微生物共生体在宿主、群落和生态系统层面的生态学中的作用提供了重要的机会，因为这些生态系统由动物主导，其生存显然与一种或几种特定共生体的获取有关。该项目通过解决自由生活的共生种群影响宿主动物建立的潜力，开始填补我们对热液喷口驱动群落结构因素的理解空白，同时也扩大了我们对宿主相关微生物对适用于整个生态系统的基本生态过程的影响的一般知识。该项目的成果将通过教育视频和直播分享给史密森学会的国家自然历史博物馆和大学运营的博物馆。研究人员还将设计和实施一个适合初中和高中班级的关于共生和热液喷口生物学的教育计划。最后，研究人员将在科学教育项目的研究和发展方面培养一群不同的本科生和研究生。该项目将重点关注蜗牛的两个姐妹属，Alviniconcha和Ifremeria，它们在西南太平洋的火山口占主导地位。在劳盆地（汤加）的火山口，三种Alviniconcha和一种Ifremeria共存。这四个物种在成年后的鳃组织中都有不同的趋化自养变形菌，这些变形菌为它们提供了大量的营养。以往研究表明，该地区的蜗牛物种分布结构与共生体化学自养代谢的关键化学基质浓度相对应，表明蜗牛物种正在根据共生体生理学向地球化学栖息地分选。目前尚不清楚这种分类是否发生在已建立的蜗牛-细菌共生关系中，或者是否环境对特定共生体的可用性的影响正在影响寄主物种的招募，因为到达和发育的蜗牛幼虫必须从环境中获得它们的共生体。本研究旨在1)通过收集幼虫、幼体和成体蜗牛来评估共生通口蜗牛的幼虫供应和种群结构；2)通过显微镜和配子、幼虫和幼体的标记基因测序来研究共生体获取的发育时间；3)使用宏基因组测序来量化环境中自由生活的共生体对到达幼虫的可用性。总之，这一系列相互关联的努力将使人们更好地了解自由生活的细菌共生种群、共生获得的时间和寄主蜗牛的生活史，以及这些事情如何相互作用来形成通风口群落。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Symbiosis with microbes is ubiquitous and critical to fundamental biological functions such as development and nutrition. Thus, the success of a host animal may depend on its ability to find and associate with its microbial partner(s). While some hosts directly transmit their symbionts from parent to offspring in order to guarantee this, acquisition of microbial symbionts from the environment is vital for the survival of many obligately-symbiotic animals. An understanding of the free-living symbiont population and how the host acquires those symbionts is fundamental to our comprehension of ecological processes in all ecosystems, yet almost nothing is known about either. Hydrothermal vent ecosystems provide important opportunities to investigate the role of microbial symbionts in host-, community-, and ecosystem-level ecology, since these ecosystems are dominated by animals whose survival is clearly linked to the acquisition of one or a few specific symbionts. This project begins to fill a gap in our understanding of the factors driving community structure at hydrothermal vents by addressing the potential for free-living symbiont populations to affect host animal establishment, while also expanding our general knowledge regarding the impact of host-associated microbes on fundamental ecological processes that apply across ecosystems. The results of this project will be shared via educational videos and live-broadcasts to the Smithsonian Institution's National Museum of Natural History and University-run museums. The investigators will also design and implement an educational program about symbiosis and hydrothermal vent biology suitable for middle and high school classes. Finally, the investigators will train a diverse group of undergraduate and graduate students in both research and the development of science educational programs. This project will focus on two sister genera of snails, Alviniconcha and Ifremeria, which predominate at vents in the southwestern Pacific. At vents in the Lau Basin (Tonga), three species of Alviniconcha and one species of Ifremeria coexist. These four species all host distinct lineages of chemoautotrophic proteobacteria in their gill tissue as adults that provide the bulk of their nutrition. Previous work in this region showed a structured snail species distribution that corresponds to the concentrations of key chemical substrates for symbiont chemoautotrophic metabolism, suggesting that snail species are sorting into geochemical habitats based on symbiont physiology. It is not clear if this sorting is occurring among established snail-bacteria symbioses, or whether environmental effects on the availability of specific symbionts are influencing the recruitment of host species, since arriving and developing snail larvae must obtain their symbionts from the environment. This study aims to 1) assess the larval supply and population structure of symbiotic vent snails via collections of larval, juvenile, and adult snails, 2) investigate the developmental timing of symbiont acquisition through microscopy and marker gene sequencing of gametes, larvae, and juveniles, and 3) use metagenomic sequencing to quantify the availability of free-living symbionts in the environment to arriving larvae. Altogether, this series of interlinked efforts will allow for an improved understanding of free-living bacterial symbiont populations, the timing of symbiont acquisition, and host snail life history, as well as how these things interact to shape vent communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.