Levels of specificity of Xylaria species associated with fungus-growing termites: a phylogenetic approach

Fungus-growing termites live in obligate mutualistic symbiosis with species of the basidiomycete genus Termitomyces, which are cultivated on a substrate of dead plant material. When the termite colony dies, or when nest material is incubated without termites in the laboratory, fruiting bodies of the ascomycete genus Xylariaappear and rapidly cover the fungus garden. This raises the question whether certain Xylariaspecies are specialised in occupying termite nests or whether they are just occasional visitors. We tested Xylariaspecificity at four levels: (1) fungus-growing termites, (2) termite genera, (3) termite species, and (4) colonies. In South Africa, 108 colonies of eight termite species from three termite genera were sampled for Xylaria. Xylariawas isolated from 69 of the sampled nests and from 57 of the incubated fungus comb samples, confirming high prevalence. Phylogenetic analysis of the ITS region revealed 16 operational taxonomic units of Xylaria, indicating high levels of Xylariaspecies richness. Not much of this variation was explained by termite genus, species, or colony; thus, at level 2-4 the specificity is low. Analysis of the large subunit rDNA region, showed that all termite-associated Xylariabelong to a single clade, together with only three of the 26 non-termite-associated strains. Termite-associated Xylariathus show specificity for fungus-growing termites (level 1). We did not find evidence for geographic or temporal structuring in these Xylariaphylogenies. Based on our results, we conclude that termite-associated Xylariaare specific for fungus-growing termites, without having specificity for lower taxonomic levels.