Social microbiome transmission predicts microbial specialization and host lifespan in a wild primate

Social interactions are proposed to provide reliable routes for microbial transmission between animals, facilitating animal-microbiome co-evolution. However, microbiome transmission remains challenging to measure in wild populations. Here we combine behavioral observations of wild baboons with repeated strain-resolved metagenomic profiling to identify individual gut microbial species that follow a dominant mode of social transmission. In an 18-year metagenomic time series from the same population, baboons with higher levels of socially transmitted species lived longer than those with lower levels of socially transmitted species. Socially transmitted species were also more stable and persistent within baboons, yet had narrower host ranges outside of baboons. Thus, social transmission is not only detectable in free-living primates, but may play a special role in both host and microbial fitness.