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 herbivoresthat show distinct preferences in the substrate choice to feed the fungus theycultivate in subterranean gardens. These ants are known to reject previouslyaccepted plants if they are unsuitable for their symbiotic fungus: a phenomenonthat involves avoidance learning [1, 2]. The purpose of this study was toanalyze the foraging preference of leaf-cutting ants in response to agrass-endophyte symbiosis that is non-toxic for cattle but reduces grasscolonization by different fungal species [3, 4]. Here,we describe how the presence of the endophyte Epichloё occultans, living inside Lolium multiflorum plants, reduces plant damage by Acromyrmex ambiguus along five foraging days.We work under the hypothesis that ant foraging preference changes over time aftertissues of endophyte-infected plants interact negatively with the symbiotic fungusof the ants. We conducted a binary choice experiment with 5 laboratory antcolonies. Each day, two different pots sown with sixteen Lolium multiflorum seeds, coming from the same population, withcontrasting levels of endophyte infection (E+: 93% and E-: 5%) were offered to oneof the ant colonies that has never been exposed to Lolium multiflorum plants before. The ants were allowed to foragefreely during 9 hours, after which, we removed the pots. At the end of each day,we counted how many tillers were damaged and estimated preference as thenatural logarithm of the reason between number of cut tillers in E- and E+ pots.We didn?t find significant differences in the damage caused by ants between potson the first day (α=0.05).But, on the fifth day of ant?s exposure to the grass-endophyte symbiosis theants damaged more tillers in E- pots than E+ pots suggesting that theypreferred the plants without infection (α=0.05). Our results show that the response ofleaf-cutting ants to anti-herbivore effects of the endophyte fungus in the hostgrass 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 infectedLolium multiflorum plants as a potentialcue that ants can use to detect endophyte presence. These findings shed considerablenew light on the consequences of the collision of different fungal symbioses. Wepropose that, to understand the complexity of this multi-symbionts andmulti-trophic levels interaction, it is necessary to expand the temporal scaleof our studies