Mammal species and functions diversified and evolved in space in response to climate and dispersal routes but they were not alone; they carry onand in their body extremely diverse communities of microorganisms. Intriguingly, these microbial communities, and especially the gut microbiome, play a key role in the fitness of the host animal, so that it is tempting to suggest that they actually co-evolved in a mutualistic way with their host. However, whether this seemingly intimate mammal–microbiota relationship is persistent and specific over evolutionary time iscontroversial and rigorous tests of co-evolution are lacking.
An important goal of my research is to quantify the importance of co-evolution in driving the relationship between host and their microbes.
To do so I use phylogenetic comparative methods to trace the evolutionary origins of gut microbial ecosystems and to measure the prevalence of co-evolution. As an example, we recently demonstrated for that co-speciations have a significant role in the evolution of mammalian gut microbiomes (Grousin*, Mazel* et al., Nat Com, 2017; *co-first authors). While co-speciation can be the result of an intimate co-evolution, it might also arise neutrally if microbes are transmitted vertically (from mother to infant) and if host speciation creates barriers to dispersion for gut microbes. In contrast to a co-evolutionary scenario, the neutral scenario does not imply a fitness interdependence between gut microbes and their host. The two scenarios predict very different outcomes in term of contribution of microbes to host health. Consistent with the co-evolutionary scenario, we found that highly co-speciating bacterial genera are systematically lost in human immune diseases. This suggest that highly co-speciating bacteria disproportionally contribute to host health and might thus have co-evolved with their host. Put together, our results suggest, for the first time, that mammals and some of their gut microbes have co-evolved for millions of years in a mutualistic way. I hope that my work will improve our understanding of the macro-evolution of host-microbe relationships, and that this will have broad medical implications.
An important goal of my research is to quantify the importance of co-evolution in driving the relationship between host and their microbes.
To do so I use phylogenetic comparative methods to trace the evolutionary origins of gut microbial ecosystems and to measure the prevalence of co-evolution. As an example, we recently demonstrated for that co-speciations have a significant role in the evolution of mammalian gut microbiomes (Grousin*, Mazel* et al., Nat Com, 2017; *co-first authors). While co-speciation can be the result of an intimate co-evolution, it might also arise neutrally if microbes are transmitted vertically (from mother to infant) and if host speciation creates barriers to dispersion for gut microbes. In contrast to a co-evolutionary scenario, the neutral scenario does not imply a fitness interdependence between gut microbes and their host. The two scenarios predict very different outcomes in term of contribution of microbes to host health. Consistent with the co-evolutionary scenario, we found that highly co-speciating bacterial genera are systematically lost in human immune diseases. This suggest that highly co-speciating bacteria disproportionally contribute to host health and might thus have co-evolved with their host. Put together, our results suggest, for the first time, that mammals and some of their gut microbes have co-evolved for millions of years in a mutualistic way. I hope that my work will improve our understanding of the macro-evolution of host-microbe relationships, and that this will have broad medical implications.