Fig. 5

Genetic heterogeneity and environment-driven adaptative evolution in the symbiotic bacteria of G. platifrons. a Schematic showing the core and clade-specific metabolic pathways involved in environmental adaptation, as indicated by metagenomic comparison. Gray arrows indicate pathways common to the genomes of both vent and seep mussel symbionts. Blue arrows indicate pathways only conserved across the seep mussel symbionts, while orange arrows indicate pathways only conserved across or detected in the vent mussel symbionts. Genes only expressed in the vent symbionts are shown in red text. b Model of the predicted mosaic pattern of adaptive environmental evolution in the symbionts of G. platifrons. The environment is the main extrinsic force maintaining genome plasticity and driving within-species differentiation, while MGEs are an intrinsic source of genetic innovation via TE rearrangement and plasmid infection. The MGE-mediated loss and gain of functional genes facilitate the adaptative evolution of symbiont functional genomes