Invasive ants suppress a native fungus but restructure fungal communities and increase richness

Organisms deploy chemical defenses against pathogens and competitors,
often resulting in coevolutionary arms races. When introduced into new
environments, non-native species may possess ‘novel weapons’ against which
native species have not evolved resistance. Ants use antifungal secretions
and microbial symbionts to defend against pathogens, but their broader
effects on soil fungi are less understood. We tested whether the invasive
ant Myrmica rubra suppressed native fungi more strongly than the native
ant Aphaenogaster picea using laboratory assays in which colonies of each
species were exposed to agar plates inoculated with a native saprotroph,
Absidia sp. Across high- and low-resource replicates, A. picea had no
effect on Absidia growth relative to controls, whereas M. rubra reduced
fungal cover, supporting the prediction that non-native ants exert
stronger antifungal effects. Moreover, M. rubra facilitated non-target
fungi colonization, including Aspergillus, Clonostachys, and Simplicillium
species. Finally, phylogenetic analysis confirmed that M. rubra
restructured fungal communities into distinct fungal assemblages. These
results suggest that invasive ants may suppress native fungi while
facilitating tolerant or self-benefiting, potentially reinforcing their
ecological success. These findings underscore the role of microbial
interactions in ant invasions and soil community dynamics.