Chemosymbiotic specificity and plasticity in thyasirid bivalves

在有机物质高度富集的海洋沉积物中（例如，靠近纸浆和造纸厂或污水排放口、水产养殖场、农业场所以及油气田），微生物降解有机物，产生有毒的还原硫；有机富集被认为是全球沿海环境面临的最大问题之一。一种特殊的小型，鲜为人知的蛤蜊（双壳类蛤科）通常是丰富环境中最早和最丰富的殖民者之一，包括在加拿大海岸线的几个地点。在共生的硫氧化细菌的帮助下，这些袋狸蛤能够在丰富的环境中茁壮成长；共生细菌是蛤蜊的另一种食物来源。与其他从深海热液喷口、冷渗漏或鲸鱼瀑布中获得类似共生体的动物不同，袋虫并不将细菌共生体保存在鳃细胞内，而是保存在鳃细胞外（细胞外）。我的研究使用尖端的观察技术来研究胸腺蛤胞外共生的特殊性，以及它如何影响它们从关联中获得的营养输入。此外，我关注不同地点之间共生体丰度的变化，并使用对宿主和共生体的营养输入进行操纵的实验，以确定对蛤蜊的影响。最后，我用分子方法研究了不同研究地点蛤蜊和共生体的身份。通过探索一种潜在的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，希望在丰富的环境中，thyasirid蛤的作用和最终的环境影响将变得清晰。这项工作对海洋生物学家、政府决策者和参与有机富集沉积物监测的科学家来说应该是重要的；因此，通过更好地了解那些适应在受干扰的海洋沉积物中生活的独特物种的作用，这项研究有望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.