Symbiotic associations between animals and microorganisms are widespread and have a profound impact on the ecology, behaviour, physiology, and evolution of the host. Research on deep-sea mussels of the genus Bathymodiolus has revealed how chemosynthetic symbionts sustain their host with energy, allowing them to survive in the nutrient-poor environment of the deep ocean. However, to date, we know little about the initial symbiont colonization and how this is integrated into the early development of these mussels. Here we analysed the early developmental life stages of B. azoricus, “B”. childressi and B. puteoserpentis and the changes that occur once the mussels are colonized by symbionts. We combined synchrotron-radiation based µCT, correlative light and electron microscopy and fluorescence in situ hybridization to show that the symbiont colonization started when the animal settled on the sea floor and began its metamorphosis into an adult animal. Furthermore, we observed aposymbiotic life stages with a fully developed digestive system which was streamlined after symbiont acquisition. This suggests that bathymodiolin mussels change their nutritional strategy from initial filter-feeding to relying on the energy provided by their symbionts. After ∼35 years of research on bathymodiolin mussels, we are beginning to answer fundamental ecological questions concerning their life cycle and the establishment of symbiosis.

中文翻译：

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走到一起——共生体收购和Bathymodiolus贻贝的早期发展

动物和微生物之间的共生关系广泛存在，并对宿主的生态、行为、生理和进化产生深远的影响。研究属深海贻贝Bathymodiolus揭示了化学合成的共生体如何维持其主机与能量，让他们在深海的营养贫乏的环境中生存。然而，迄今为止，我们对最初的共生体定植以及如何将其融入这些贻贝的早期发育知之甚少。在这里，我们分析了B. azoricus，“B”的早期发育生命阶段。childressi和B. puteoserpentis以及贻贝被共生体定殖后发生的变化。我们结合基于同步辐射的 μCT、相关光和电子显微镜以及荧光原位杂交，表明当动物在海底定居并开始变态成成年动物时，共生体定植就开始了。此外，我们观察到具有完全发育的消化系统的非共生生命阶段，该消化系统在共生体获得后进行了精简。这表明深海藻素贻贝改变了它们的营养策略，从最初的滤食改为依赖共生体提供的能量。经过大约 35 年对深海藻类贻贝的研究，我们开始回答有关它们的生命周期和建立共生关系的基本生态问题。