Delayed avoidance of endophyte-infected Lolium multiflorum plants by leaf-cutting ants after two fungal symbioses collision

FIORENZA, J; FERNANDEZ, P; OMACINI, M

Salamanca

Simposio; 10th International Symposium on Fungal endophytes of grasses; 2018

10th International Symposium on Fungal endophytes of grasses

Leaf‐cutting ants are polyphagous herbivores that show distinct preferences in the substrate choice tofeed the fungus they cultivate in subterranean gardens. These ants are known to reject previously accepted plantsif they are unsuitable for their symbiotic fungus: a phenomenon that involves avoidance learning[1,2]. The purposeof this study was to analyze the foraging preference of leaf‐cutting ants in response to a grass‐endophyte symbiosisthat is non‐toxic for cattle but reduces grass colonization by different fungal species[3,4]. Here, we describe how thepresence of the endophyte Epichloё occultans, living inside Lolium multiflorum plants, reduces plant damage byAcromyrmex ambiguus along five foraging days. We work under the hypothesis that ant foraging preferencechanges over time after tissues of endophyte‐infected plants interact negatively with the symbiotic fungus of theants. We conducted a binary choice experiment with 5 laboratory ant colonies. Each day, two different pots sownwith sixteen Lolium multiflorum seeds, coming from the same population, with contrasting levels of endophyteinfection (E+: 93% and E−: 5%) were offered to one of the ant colonies that has never been exposed to Loliummultiflorum plants before. The ants were allowed to forage freely during 9 h, after which, we removed the pots. Atthe end of each day, we counted how many tillers were damaged and estimated preference as the naturallogarithm of the reason between number of cut tillers in E− and E+ pots. We didn?t find significant differences inthe damage caused by ants between pots on the first day (α=0.05). But, on the fifth day of ant?s exposure to thegrass‐endophyte symbiosis the ants damaged more tillers in E‐ pots than E+ pots suggesting that they preferred theplants without infection (α=0.05). Our results show that the response of leaf‐cutting ants to anti‐herbivore effectsof the endophyte fungus in the host grass can be delayed in time, and probably related to the ant?s response to afungus warning. We are exploring the volatile organic compounds produced by infected Lolium multiflorum plantsas a potential cue that ants can use to detect endophyte presence. These findings shed considerable new light onthe consequences of the collision of different fungal symbioses. We propose that, to understand the complexity ofthis multi‐symbionts and multi‐trophic levels interaction, it is necessary to expand the temporal scale of ourstudies