Chemosymbiotic specificity and plasticity in thyasirid bivalves

在高度富含有机质的海洋沉积物中(例如纸浆和造纸厂或排污口附近、水产养殖场、农业场地以及气田和油田)，微生物降解有机物，产生有毒的还原硫；有机富集化被认为是全世界沿海环境面临的最大问题之一。一种特殊的鲜为人知的小型蛤类(双壳科)往往是丰富环境的第一批也是最丰富的殖民者之一，包括加拿大海岸线的几个地点。在鳃中共生的硫氧化细菌的帮助下，这些百里香文蛤能够在丰富的环境中茁壮成长；细菌共生体是文蛤的额外食物来源。与深海热液喷口、冷泉或鲸鱼瀑布中具有类似共生环境的其他动物不同，海鞘动物不会将它们的细菌共生体保留在鳃细胞内，而是保持在它们的外部(细胞外)。我的研究使用了尖端的观察技术来研究在百里香中胞外共生的特殊性，以及它如何影响它们从这种关联中获得的营养输入。此外，我还重点研究了不同地点之间共生体丰度的差异，并通过实验对寄主和共生体的营养输入进行了操纵，以确定对文蛤的影响。最后，用分子生物学的方法对不同研究地点的文蛤和共生体进行了鉴定。通过探索可能不那么僵硬的共生关系如何有利于在不断变化的环境中生存，人们希望能够清楚地认识到，百里香在丰富的环境中的作用和最终的环境影响。这项工作对于海洋生物学家、政府政策制定者和参与监测有机富集物的科学家来说应该是重要的；因此，这项研究预计将通过更好地了解适应在受干扰的海洋沉积物中生活的独特物种的作用，使所有加拿大人受益。

In marine sediments highly enriched with organic matter (e.g. near pulp and paper mill or sewage outfalls, aquaculture pens, agricultural sites, and gas and oil fields), microbes degrade organic matter, producing toxic reduced sulphur; organic enrichment is recognized as being one of the greatest problems facing coastal environments worldwide. A particular group of small, poorly-known clams (bivalve family Thyasiridae) is often among the first and most abundant colonists of enriched environments, including in several sites along the Canadian coastline. Those thyasirid clams are able to thrive in enriched environments with the help of symbiotic, sulphur-oxidizing bacteria living in their gills; bacterial symbionts are an additional food source for the clams. As opposed to other animals with similar symbioses from deep-sea hydrothermal vents, cold seeps or whale falls, thyasirids do not keep their bacterial symbionts within gill cells, but outside them (extracellularly). My research uses cutting-edge observational techniques to study the particularities of extracellular symbiosis in thyasirid clams, and how it affects the nutritional input they gain from the association. Also, I focus on the variability in symbiont abundance between different sites, and I use experiments in which nutritional inputs to the host and symbiont are manipulated, to determine the impacts on the clams. Finally, I study the identity of the clams and symbionts in different study sites, using molecular approaches. By exploring how a potentially less rigid symbiosis might be beneficial for surviving in changing environments, it is hoped that the role and eventual environmental impacts of thyasirid clams in enriched environments will become clear. This work should be important for marine biologists, government policy decision-makers, and scientists involved in the monitoring of organically enriched sediments; as such, this research is expected to benefit all Canadians through a better understanding of the role of those unique species that are adapted for living in disturbed marine sediments.