1st Place: Phylosymbiosis in fungus-gardening ants Trachymyrmex

Fungus-gardening ants (tribe Attini) maintain a complex symbiotic relationship with their fungus gardens and associated bacteria (microbiomes). The bacteria found in the ant microbiome play roles ranging from nitrogen fixation to antibiotic compound production. The strong cophylogenetic relationship between the ants and their fungi has been well studied, but aside from a few bacterial taxa (e.g., Pseudonocardia), the coevolution between ants and their microbiomes has not been explored in great detail. In an attempt to better understand this ant-microbiome relationship, we checked for ant-microbiome phylosymbiosis by determining if the evolutionary history of ant microbiomes reflected the evolutionary history of their associated ant species. We included five species of fungus-gardening ants in our analysis (Trachymyrmex arizonensis, T. pomonae, T. smithi, T. septentrionalis, and Mycetomoellerius turrifex) as well as the ant microbiomes and the microbiomes of the associated fungal gardens. We conducted both a genetic matrix comparison and a topological phylogenetic comparison. We found that closely related ants have significantly more similar microbiomes, and the evolutionary history of the ants and their microbiomes exhibits significant topological congruence. A follow-up analysis incorporating geographic data was conducted to evaluate the potential effect of geography on this ant-microbiome evolutionary relationship. Overall, our results present strong evidence for phylosymbiosis occurring between fungus-gardening ants and the microbiomes associated with both ants and fungus.