Mycelial carton galleries of Azteca brevis (Formicidae) as a multi-species network

Apart from growing fungi for nutrition, as seen in the New World Attini, ants cultivate fungi for reinforcement of the walls of their nests or tunnel-shaped runway galleries. These fungi are grown on organic material such as bark, epiphylls or trichomes, and form stable 'carton structures'. In this study, the carton of the runway galleries built by Azteca brevis (Formicidae, Dolichoderinae) on branches of Tetrathylacium macrophyllum (Flacourtiaceae) is investigated. For the first time, molecular tools are used to address the biodiversity and phylogenetic affinities of fungi involved in tropical ant carton architecture, a previously neglected ant-fungus mutualism. The A. brevis carton involves a complex association of several fungi. All the isolated fungi were unequivocally placed within the Chaetothyriales by DNA sequence data. Whereas five types of fungal hyphae were morphologically distinguishable, our DNA data showed that more species are involved, applying a phylogenetic species concept based on DNA phylogenies and hyphal morphology. In contrast to the New World Attini with their many-to-one (different ant species-one fungal cultivar) pattern, and temperate Lasius with a one-to-two (one ant species-two mutualists) or many-to-one (different ant species share the same mutualist) system, the A. brevis-fungi association is a one-to-many multi-species network. Vertical fungus transmission has not yet been found, indicating that the A. brevis-fungi interaction is rather generalized.