Arêdes, A., Rodríguez, J., Bailez, O., dos Santos Lima, J.C., Canela, M.C. & Viana-Bailez, A.M.

Aversive learning as a behavioural mechanism of plant selection in the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae)

The survival of leaf-cutting ants depends on their ability to select suitable resources for their fungal symbiont. Plant selection may be influenced by innate or acquired preferences. We investigated the learning processes involved in resource selection in Atta sexdens (Linnaeus, 1758) and the role of symbiotic fungi. Subcolonies regularly fed leaves of one plant species (conditioning plant) were later tested for their preference between leaves of the conditioning plant and leaves of other plant species. In a second experiment, subcolonies fed with a plant species impregnated with fungicide (aversive conditioning) were subjected to a preference test between the conditioning plant (treatment) and another species (control), both without fungicide. In a third experiment, subcolonies subjected to aversive conditioning were allowed to choose between leaves treated or untreated with fungicide. In a fourth experiment, aversively conditioned subcolonies were allowed to choose between paper fragments treated with odours of aversive or nonaversive plants. In a fifth experiment, conditioned subcolonies were allowed to choose between leaves from a different plant impregnated or not with odours from aversive plants. In all five experiments, the number of transported fragments was statistically compared between treatment and control subcolonies. In a sixth experiment, fungus garden extracts of subcolonies treated or untreated with fungicide were analysed by gas chromatography coupled to mass spectrometry. Ants did not exhibit appetitive conditioning to suitable plants, but harmful resources induced delayed rejection and decreased preference, confirming the occurrence of aversive conditioning. Safe resources impregnated with odours from harmful resources were rejected by the ants, indicating that olfactory learning participates in the plant selection process. Harmful resources induced changes in the chemical profile of symbiotic fungi and caused a delayed rejection behaviour in worker ants. Odours of harmful plants are linked to food rejection behaviour through associative learning and inhibit future collection of these plants. Plant selection in A. sexdens seems to be based on recognition of resources that are harmful to symbiotic fungi rather than on recognition of adequate resources.

Open access, licensed under CC BY 4.0. © 2022 The Author(s).

Arêdes, A., Rodríguez, J., Bailez, O., dos Santos Lima, J.C., Canela, M.C. & Viana-Bailez, A.M.

Aversive learning as a behavioural mechanism of plant selection in the leaf-cutting ant Atta sexdens (Hymenoptera: Formicidae)

The survival of leaf-cutting ants depends on their ability to select suitable resources for their fungal symbiont. Plant selection may be influenced by innate or acquired preferences. We investigated the learning processes involved in resource selection in Atta sexdens (Linnaeus, 1758) and the role of symbiotic fungi. Subcolonies regularly fed leaves of one plant species (conditioning plant) were later tested for their preference between leaves of the conditioning plant and leaves of other plant species. In a second experiment, subcolonies fed with a plant species impregnated with fungicide (aversive conditioning) were subjected to a preference test between the conditioning plant (treatment) and another species (control), both without fungicide. In a third experiment, subcolonies subjected to aversive conditioning were allowed to choose between leaves treated or untreated with fungicide. In a fourth experiment, aversively conditioned subcolonies were allowed to choose between paper fragments treated with odours of aversive or nonaversive plants. In a fifth experiment, conditioned subcolonies were allowed to choose between leaves from a different plant impregnated or not with odours from aversive plants. In all five experiments, the number of transported fragments was statistically compared between treatment and control subcolonies. In a sixth experiment, fungus garden extracts of subcolonies treated or untreated with fungicide were analysed by gas chromatography coupled to mass spectrometry. Ants did not exhibit appetitive conditioning to suitable plants, but harmful resources induced delayed rejection and decreased preference, confirming the occurrence of aversive conditioning. Safe resources impregnated with odours from harmful resources were rejected by the ants, indicating that olfactory learning participates in the plant selection process. Harmful resources induced changes in the chemical profile of symbiotic fungi and caused a delayed rejection behaviour in worker ants. Odours of harmful plants are linked to food rejection behaviour through associative learning and inhibit future collection of these plants. Plant selection in A. sexdens seems to be based on recognition of resources that are harmful to symbiotic fungi rather than on recognition of adequate resources.

Open access, licensed under CC BY 4.0. © 2022 The Author(s).