Is there convergence of gut microbes in blood-feeding vertebrates?

Animal microbiomes play an important role in dietary adaptation, yet the extent to which microbiome changes exhibit parallel evolution is unclear. Of particular interest is adaptation to extreme diets, such as blood, which poses special challenges in its content of proteins and lack of essential nutrients. In this study, we assessed taxonomic signatures (by 16S rRNA amplicon profiling) and potential functional signatures (inferred by PICRUSt) of hematophagy in three classes of vertebrates: birds, bats, and fish. We also compare the results to microbiome data from hematophagous arthropods. Our goal was to test three alternative hypotheses: no convergence of microbiomes, convergence in taxonomy, and convergence in function. We find a statistically significant effect of hematophagy in terms of microbial taxonomic convergence, although this effect is small compared to the differences found between hematophagous and non-hematophagous species within the different host clades. We also found a small effect of convergence at the predicted functional level, although it is possible that the lack of metagenomic data and the poor representation of microbial lineages adapted to hematophagy in genome databases limited the power of this approach. The results provide a paradigm for exploring convergent microbiome evolution replicated with independent contrasts in multiple host lineages.