How Escovopsis weberi attacks the garden fungus of leaf cutting ants
The specialized parasite E. weberi can overpower the symbiotic fungus Leucoagaricus gongylophorus of leaf cutting ants and thus threaten the survival of the whole nest. Previous experiments revealed that E. weberi can kill L. gongylophorus without direct contact, suggesting that it makes use of toxins. Therefore, we set out to identify the secondary metabolites from E. weberi.
E. weberi produces emodin (1), cycloarthropsone (2) and a variety of shearinines, including the novel shearinine L (3) and M (4).
Figure 1 A) Secondary metabolites from E. weberi and B) agar diffusion assays against L. gongylophorus (18 d, PDA medium), emodin (1) 0.66 mM, cycloarthropsone (2) 0.82 mM) and control.
Emodin (1) and cycloarthropsone (2) are toxic for L. gongylophorus. Emodin (1) also strongly inhibited Actinomyces symbionts from leaf cutting ants. Shearinine L (3) instead did not inhibit L. gongylophorus and also did not exhibit activity against leaf cutting ants. Instead the ants recognized shearinine L (3) and thus may use it as cue to initiate defense demonstrating the evolutionary arms race between the involved parties.
B. Dhodary, M. Schilg, R. Wirth, and D. Spiteller, 2018 Chemistry- A European Journal, epub ahead of print.