A bird's eye view of phylosymbiosis: weak but significant signatures of phylosymbiosis among all 15 species of cranes

In numerous animal clades, the evolutionary history of host species drives patterns of gut microbial community structure, resulting in more divergent microbiota with increased phylogenetic distance between hosts. This phenomenon, termed phylosymbiosis, has been observed in diverse evolutionary lineages, but never in birds. Previous tests of phylosymbiosis among birds have been conducted using wild individuals, and thus interspecific differences in diet and environment may have masked a phylogenetic signal. Therefore, we tested for phylosymbiosis among all 15 species of cranes (Gruidae) housed in the same captive environment and maintained on identical diets. Using 16S rRNA sequencing, we demonstrated that crane species harbor distinct gut microbiota that were congruent with interspecific phylogenetic relationships. The strength of these findings were increased by the inclusion of absolute abundance of microbial taxa (rather than only relative abundance) derived from sequencing-based inventories and microbial densities determined by flow cytometry. These results provide the first evidence of phylosymbiosis in birds. However, the signal is much weaker compared to other animal groups, especially mammals. We discuss the potential differences between birds and mammals, such as transmission routes and host filtering, that may underlie the differences in the strength of phylosymbiosis.