The interplay of symbiotic beings in the Pampa: the encounter between an alien grass and leaf‐cutting ants

Abstract

Symbiotic relationships across trophic levels influence invasions. Although Epichlo€e endophytesare often linked to forage grasses spread through alkaloid-mediated herbivore resistance,this link oversimplifies a complex, multifactorial process. We investigate whether thisfungal endophyte interacts with the fungus garden of the native leaf-cutting ant Acromyrmexambiguus by inducing the release of a widespread green leaf volatile, thereby altering its foragingbehavior. We conducted 5-d choice experiments to assess ant preferences for leaves and seeds ofLolium multiflorum plants, either infected (E+) or uninfected (E) with Epichlo€e occultans,along with a Petri dish assay to evaluate the effects of (Z)-3-hexenyl acetate (Z3-HAC) on thegrowth of Leucoagaricus gongylophorus, ants’ mutualistic fungi. Ants exhibited delayed rejection for E+ plants while showing no preference for seeds. Invitro, Z3-HAC promoted fungal growth away from volatile sources. These findings suggest that mutualistic fungi of a grass (alien) and its herbivore (native)shape their defense strategies in Pampean grasslands. Z3-HAC’s effects extend beyond directplant-herbivore interactions, signaling antagonistic fungi within the fungal garden withoutacting as a novel weapon. This study highlights the importance of integrating microbial networksinto invasion ecology frameworks to understand the consequences of co-introducedplants and symbionts.