Edited by Bert Hölldobler, Arizona State University, Tempe, AZ, and approved August 17, 2018 (received for review June 1, 2018)
Desert ants have been shown to use olfaction to pinpoint food and find their nest after far-reaching foraging runs. Here we show that the ants can learn new food and nest odors and that they posses two distinct memories for both contexts. While ants need several training trials to learn a nest odor, and forget about this odor shortly after training has stopped, they learn food odors after one trial, remember them over a lifetime, and can remember at least 14 different food odors. These different memory characteristics make sense, as food is unpredictable and ants might experience many different food items in consecutive foraging runs, while the nest odor will not dramatically change during an ant’s lifetime.
The desert ant Cataglyphis fortis inhabits the North African saltpans where it individually forages for dead arthropods. Homing ants rely mainly on path integration, i.e., the processing of directional information from a skylight compass and distance information from an odometer. Due to the far-reaching foraging runs, path integration is error-prone and guides the ants only to the vicinity of the nest, where the ants then use learned visual and olfactory cues to locate the inconspicuous nest entrance. The learning of odors associated with the nest entrance is well established. We furthermore know that foraging Cataglyphis use the food-derived necromone linoleic acid to pinpoint dead insects. Here we show that Cataglyphis in addition can learn the association of a given odor with food. After experiencing food crumbs that were spiked with an innately neutral odor, ants were strongly attracted by the same odor during their next foraging journey. We therefore explored the characteristics of the ants’ food-odor memory and identified pronounced differences from their memory for nest-associated odors. Nest odors are learned only after repeated learning trials and become ignored as soon as the ants do not experience them at the nest anymore. In contrast, ants learn food odors after a single experience, remember at least 14 consecutively learned food odors, and do so for the rest of their lives. As an ant experiences many food items during its lifetime, but only a single nest, differentially organized memories for both contexts might be adaptive.
Author contributions: R.H. and M.K. designed research, performed research, analyzed data, and wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Published under the PNAS license.
