Bronze Age coprolites unveil the buffering role of the gut microbiota in the dietary adaptation of dogs to domestication

Dog evolution has long been debated, particularly with regards to the origin of domestication and its effects on the genome, but little is known about the role of the gut microbiome during the recent canine evolutionary history. We sequenced the metagenome of 13 canine coprolites dated ca. 3,600-3,450 y ago from the Bronze Age archaeological site of Solarolo (Italy), which housed a complex farming community. The microbiome structure of Solarolo dogs revealed continuity with that of modern dogs, but it also shared some features with the wild wolf microbiome, as a kind of transitional state between them. The dietary niche, as inferred from the microbiome composition, was omnivorous, with evidence of consumption of starchy agricultural foods. Interestingly, the gut microbiome from Solarolo was particularly enriched in sequences encoding alpha-amylases and complemented a low copy number of the host amylase (AMY2B) gene. These findings suggest that Neolithic dogs could have responded to the transition to a starch-rich diet by expanding microbial functionalities devoted to starch catabolism. Such a microbiome adaptive mechanism would have compensated for delayed host response to the new primarily abundant plant food resources, available from companionship with Bronze Age agriculturalists.