The Apterostigma auriculatum fungus-farming ant species group: Phylogenomic species delimitation and ant-fungus symbiotic coevolution

The fungus-farming ant genus Apterostigma, occurring in the Neotropics and the Caribbean, is divided into three species groups based on morphological and molecular data: the auriculatum group (13 spp), the pilosum group (30 spp), and the megacephala group (1 sp). Associations between Apterostigma species and their fungal cultivars are strongly correlated with phylogeny. Species in the auriculatum group cultivate leucocoprineaceous fungi, the ancestral fungal cultivar of all fungus-farming ants. Species in the pilosum group cultivate pterulaceous fungi, presumably as a result of a transition from a leucocoprineaceous to a pterulaceous cultivar in their most recent common ancestor. Finally, the single species in the megacephala group is the only lower fungus-farming ant known to cultivate the highly modified and most recently evolved higher cultivar, cultivated by most leaf-cutter ants. To study the associations between the ants and their fungi, Apterostigma species need to be properly delimited. Our dataset includes 142 OTUs (58 belonging to the auriculatum group), including eleven paratypes (5 belonging to auriculatum group), and ~2300 UCE loci. Preliminary results suggest that the auriculatum group contains at least nine new species and that major clades within the group originated very rapidly around 10–12 Ma, coinciding with the demise of the Pebas Lake system.