Are ants botanists? Ant associative learning of plant chemicals mediates foraging for carbohydrates

Abstract

Abstract 1. Although associative learning is widespread across animals, its ecological importance is difficult to assess because learning is rarely studied in the field, where informative cues are juxtaposed against complex backgrounds of uninformative noise. 2. Ants rely heavily on chemical cues for foraging and engage in many ecologically important interactions with plants. Nevertheless, little is known about the role of associative learning of plant chemicals in ant foraging for carbohydrates. 3. In a field setting, the present study investigated whether the distantly related ant species Formica podzolica (Formicinae subfamily) and Tapinoma sessile (Dolichoderinae subfamily) exhibited associative learning of the chemical cues from two co‐occurring plant species that are taxonomically and chemically distinct (Asteraceae: Helianthella quinquenervis and Apiaceae: Ligusticum porteri ). 4. For two consecutive summers, ants were trained to forage from artificial sugar‐rich baits associated with the leaf chemicals from either H. quinquenervis or L. porteri for 24 h, after which a two‐choice test was deployed to assess whether ants would be more likely to select baits associated with the same (versus different) plant chemicals on which they had been trained. 5. The present study demonstrates associative learning of chemicals from both plant species, and these effects were consistent between ant species and years; training increased bait occupancy from 42% on the untrained scent to 66% on the trained scent. These results indicate that associative odour‐learning may be widespread across ants and serve as an important mechanism mediating ant selection of resources.