Phylogenetic analysis of termite-associated Xylaria from Africa reveals hidden diversity

Fungus-farming termite colonies host members of the genus Xylaria as stow-away fungi that emerge from deteriorating fungal gardens (combs) or dying termite nests. Fungus-farming termites originated in Africa, where the highest host diversity - eleven termite genera - exists, and later colonised parts of Asia, where five extant termite genera are known. Theory predicts that symbiont diversity should correlate with host diversity, but while 17 termite-associated Xylaria species have been described from Asia, a mere three African species have been formally described. This suggests that the diversity of termite-associated Xylaria in Africa is underestimated due to under-sampling. To test this, we obtained 34 Xylaria isolates from 20 termite colonies in Côte d'Ivoire and placed them in a multi-locus phylogenetic analysis alongside 278 Xylaria and outgroup specimens. This revealed 18 putatively novel Xylaria species, confirming our hypothesis. In addition, our findings revealed the capacity for termite-associated Xylaria species to colonize fungus gardens associated with diverse termite host genera, and that individual termite colonies can host multiple Xylaria species. Given the relatively limited scope of our sampling, including Xylaria strains derived from only four of 11 farming termite genera, it is imperative that substantial diversity likely remains to be discovered, particularly in Africa.