The ant-plant Hirtella physophora (Chrysobalanaceae), the ant Allomerus decemarticulatus (Myrmicinae) and an Ascomycete fungus, Trimmatostroma sp., form a tripartite association. The fungus improves nutrient uptake by the host plant, but hitherto it has been unclear whether it has an indirect or a direct role in transferring nutrients to the plant.

Hirtella physophora branch bearing mature leaves with ant domatia (leaf pouches located at the base of the lamina where the associated ants nest) and the gallery under the stem that the ants use as a trap to ambush prey.
(A) Hirtella physophora branch bearing mature leaves with ant domatia (leaf pouches located at the base of the lamina where the associated ants nest) and the gallery under the stem that the ants use as a trap to ambush prey. (B) Portion of a stem showing the trap built by Allomerus decemarticulatus ants using the plant’s trichomes, which they assemble into a frame on which the fungal mycelium of Trimmatrostoma sp., which reinforces the structure of the gallery, then grows. Source: Leroy et al. 2017

Identification of hyphae inside stem tissue and a stable nitrogen isotope tracer experiment combined with NanoSIMS imaging reveals that 15N-enriched cells are not diffuse. Leroy et al. show that in this ant-plant system a fungus actively transfers nitrogen from a 15N-labelling solution to the plant’s stem tissues, suggesting that the fungus may play a role in transporting nutrient-derived ant waste. The complex trophic structure of ant-plant interactions is shown to rely upon the presence of the fungus. The study provides insight into the potentially important nutritional aspects and tradeoffs involved in myrmecophyte–ant mutualisms.