TY - JOUR T1 - Becoming symbiotic – the symbiont acquisition and the early development of bathymodiolin mussels JF - bioRxiv DO - 10.1101/2020.10.09.333211 SP - 2020.10.09.333211 AU - Maximilian Franke AU - Benedikt Geier AU - Jörg U. Hammel AU - Nicole Dubilier AU - Nikolaus Leisch Y1 - 2020/01/01 UR - http://biorxiv.org/content/early/2020/10/09/2020.10.09.333211.abstract N2 - 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.Competing Interest StatementThe authors have declared no competing interest. ER -