New View on Origin of Attine Ant–Fungus Mutualism: Exploitation of a Preexisting Insect–Fungus Symbiosis (Hymenoptera: Formicidae)

Abstract

Abstract Current hypotheses on the origin of the fungus–attine ant (Hymenoptera: Formicidae) symbiosis propose, as an ancestral first step in the development of fungal cultivation, fortuitous feeding on fungi growing adventitiously on substrates such as rotting wood, insect parts, seeds stored by ants in nests, regurgitated infrabuccal pellets, free-living soil fungi, or mycorrhizae. However, feeding-deterrent fungi regularly colonize these substrates. De novo feeding on these fungi by the attine ancestor is unlikely because the almost universal presence of mycotoxins on adventitious fungi is a formidable barrier to mycophagy. In addition, there is no evolutionary history of mycophagy in the Hymenoptera. Instead, I propose that attine mycophagy began from opportunistic, selective feeding on wood-colonizing fungi previously “domesticated” by other insects: ambrosia beetles: (Coleoptera: Curculionidae: Scolytinae or Platypodinae); and less likely, woodwasps (Hymenoptera: Siricoidea). Attine ancestors forage...