Interactions among Escovopsis, Antagonistic Microfungi Associated with the Fungus-Growing Ant Symbiosis

Fungi in the genus Escovopsis (Ascomycota: Hypocreales) are prevalent associates of the complex symbiosis between fungus-growing ants (Tribe Attini), the ants’ cultivated basidiomycete fungi and a consortium of both beneficial and harmful microbes found within the ants’ garden communities. Some Escovopsis spp. have been shown to attack the ants’ cultivated fungi, and co-infections by multiple Escovopsis spp. are common in gardens in nature. Yet, little is known about how Escovopsis strains impact each other. Since microbe–microbe interactions play a central role in microbial ecology and evolution, we conducted experiments to assay the types of interactions that govern Escovopsis–Escovopsis relationships. We isolated Escovopsis strains from the gardens of 10 attine ant genera representing basal (lower) and derived groups in the attine ant phylogeny. We conducted in vitro experiments to determine the outcome of both intraclonal and interclonal Escovopsis confrontations. When paired with self (intraclonal interactions), Escovopsis isolated from lower attine colonies exhibited antagonistic (inhibitory) responses, while strains isolated from derived attine colonies exhibited neutral or mutualistic interactions, leading to a clear phylogenetic pattern of interaction outcome. Interclonal interactions were more varied, exhibiting less phylogenetic signal. These results can serve as the basis for future studies on the costs and benefits of Escovopsis coinfection, and on the genetic and chemical mechanisms that regulate the compatibility and incompatibility observed here.