Fig. 1

The Leucoagaricus gongylophorus fungal cultivar produces gongylidia as specialized nutritional reward structures to feed leafcutter ants. A–C Gongylidium cells are typically depicted as a bulb at the end of a filament in the apical hyphal compartment separated by a septum (arrowheads). D Gongylidia frequently exhibit more complex branching patterns, with bulbs between filaments or in lateral branches of single hyphal cells delimited by septa. E Each gongylidium cell contains a single large vacuole (arrowheads). F Individual gongylidium cells are polykaryotic (Kooij et al. 2015), meaning that they have many haploid nuclei (white dots visualized using DAPI staining). Here, we show that in mature non-branching gongylidium cells, these nuclei occur at the base of the bulb (below a single large vacuole) and in the filament. G Staphylae grow in discrete patches at the surface of the fungus garden matrix in the middle garden stratum (arrowheads). H Gongylidium cells have thin cell walls ranging from 120 to 220 nm (cw). Images produced by light microscopy (panels A, D, F), fluorescence microscopy stained with DAPI (panel E), SEM (panels B, C, G) and TEM (panel H). Scale bars: A-F = 20 μm, G = 100 μm, H = 200 nm