More fungi than legs: the first fungal microbiome for a fungus-eating millipede (Colobognatha)

Fungi are widely consumed across the animal kingdom for nutritional and defensive benefits. Millipedes, among the first air-breathing land animals, were also among the first terrestrial fungivores. As detritus-eating omnivores, most millipedes regularly consume fungi. Millipede diets diverged [~]200 million years ago, when obligate fungivorous millipedes (subterclass Colobognatha) diverged from their detritivorous counterparts. Despite their global distribution and uncommon diet, little is known about the association between Colobognaths and the fungi they consume. In 2019, surveys of fungal communities associated with the Colobognath Brachycybe lecontii revealed associations with at least 176 genera of culturable fungi. Given the known biases of culture-based approaches, a more comprehensive survey of B. lecontiis fungal microbiome using amplicon sequencing was undertaken. In this study, we generated amplicon sequence data to look for associations between fungi and B. lecontii, and to determine if patterns of fungal diversity are millipede- or habitat-driven. Altogether, the fungal microbiome of B. lecontii encompassed 620 fungal genera and 100 orders. Despite much greater observed fungal diversity in the amplicon-based study, sampling was likely not sufficient to capture the full diversity of fungi associated with B. lecontii. Taxonomic and functional diversity were significantly influenced by site and colony, indicating that community structure is shaped by geography and habitat. It remains unknown whether these findings are representative of the larger patterns of fungal diversity for the entire millipede subterclass. Nevertheless, the obligate fungivorous lifestyle employed by these long-extant animals may provide important clues regarding fungal diversity and function.