Abstract
New associations have recently been discovered between arboreal ants that live on myrmecophytic plants, and different groups of fungi. Most of the – usually undescribed – fungi cultured by the ants belong to the order Chaetothyriales (Ascomycetes). Chaetothyriales occur in the nesting spaces provided by the host plant, and form a major part of the cardboard-like material produced by the ants for constructing nests and runway galleries. Until now, the fungi have been considered specific to each ant species. We focus on the three-way association between the plant Tetrathylacium macrophyllum (Salicaceae), the ant Azteca brevis (Formicidae: Dolichoderinae) and various chaetothyrialean fungi. Azteca brevis builds extensive runway galleries along branches of T. macrophyllum. The carton of the gallery walls consists of masticated plant material densely pervaded by chaetothyrialean hyphae. In order to characterise the specificity of the ant–fungus association, fungi from the runway galleries of 19 ant colonies were grown as pure cultures and analyzed using partial SSU, complete ITS, 5.8S and partial LSU rDNA sequences. This gave 128 different fungal genotypes, 78% of which were clustered into three monophyletic groups. The most common fungus (either genotype or approximate species-level OTU) was found in the runway galleries of 63% of the investigated ant colonies. This indicates that there can be a dominant fungus but, in general, a wider guild of chaetothyrialean fungi share the same ant mutualist in Azteca brevis.
Highlights
It is clear that microorganisms are major partners in obligate interactions between ants and plants
Other examples of ant–plant–fungus interactions have been found recently in different groups of non-attine ants, where ascomycete fungi are cultivated in domatia or on a cardboard-like construction material [4,5,6,7]
Cultures Pure cultures of carton fungi were obtained from carton material of host trees colonised by Azteca brevis
Summary
It is clear that microorganisms are major partners in obligate interactions between ants and plants. Other examples of ant–plant–fungus interactions have been found recently in different groups of non-attine ants, where ascomycete fungi are cultivated in domatia (nesting spaces provided by host plants) or on a cardboard-like construction material (named ‘‘carton’’ in ant-plant literature) [4,5,6,7]. Such ant–plant–fungus associations have been described from Africa, America and Asia and involve a wide range of plant lineages associated with an wide range of ant groups [7]. They have since been found in the walls of free-hanging canopy ant nests in the Palaeotropics [11,12] and in the Neotropics, where ants use fungus-infused, carton-like material to construct tunnel systems called ‘‘runway galleries’’ along branches of their host trees [6,13,14] (Figure 1A–D)
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