Fig. 4

Model for the hierarchical differentiation of Bathymodiolus symbionts. The differently colored symbiotic bacteria represent different strains of the conspecific bacteria in both free-living and endosymbiotic phases. The large arrows represent environmental acquisition of free-living symbionts by the mussel hosts. An intervening physical barrier, in this case the Easter Microplate region, isolates EPR + GAR and PAR populations of the symbiotic bacteria