Multiple evolutionary origins lead to diversity in the metabolic profiles of ambrosia fungi

Ambrosia fungi are an ecological assemblage cultivated by ambrosia beetles as required nutrient sources. This mutualism evolved in multiple beetle and fungus lineages. Whether convergence in ecology led to convergent metabolism in ambrosia fungi is unknown. We compared the assimilation of 190 carbon sources in five independent pairs of ambrosia fungi and closely related, non-ambrosial species. Ecological convergence versus phylogenetic divergence in carbon source use was tested using variation partitioning. We found no convergence in carbon utilization capacities. Instead, metabolic variation was mostly explained by phylogenetic relationships. In addition, carbon usage in ambrosia fungi was equally diverse as that in non-ambrosial species. Thus, carbon metabolism of each ambrosia fungus is determined by its inherited metabolism, not the transition towards symbiosis. In contrast to other fungus-farming systems of termites and attine ants, the fungal symbionts of ambrosia beetles are functionally diverse, reflecting their independent evolutionary origins.