A blog post highlighting the article by C. A. Freas & K. Cheng in Insectes Sociaux
By Cody A Freas and Ken Cheng
Imagine that you travel from your house to your favourite restaurant by walking 10 blocks due west and then need to return home. Under normal circumstances you would simply walk back 10 blocks due east. Ant foragers travelling from home to find food, can easily return to the nest in this situation through a process called path integration. During path integration, ants count their steps to estimate distance and use the sky to keep track of their current direction, combining these two measurements to travel back home. Now let’s imagine a less conventional trip. After travelling 10 blocks to the west, you leave the restaurant and are suddenly transported 10 blocks south of home. The first time this occurs you may have some difficulty, yet if this happens every time you make this trip, you would most likely become rather talented at managing this new homeward route. Humans and other animals can deal with unusual navigational problems such as teleportation by using familiar visual cues like landmarks in their environment (Warren et al. 2017).
Ants can also learn to adjust their homeward trip when the outgoing and incoming journeys do not match, by shifting the direction of their path integration system. Ant foragers will keep track of their direction and distance on both the outbound and inbound portions of their foraging trips. On succeeding trips, an ant can learn to shift its homeward direction based on experience during previous trips, which is called calibration. Earlier work involving these shifts in ants has focused on Cataglyphis fortis, a north African species living in environments with no landmarks where these foragers are able to partially shift their homeward heading after being displaced every time they collect food from a feeder (Collett et al. 1999; Wehner et al. 2002). Yet these foragers are unable to fully shift their homeward direction to the correct nest direction even after many trips, instead taking a compromise direction. In the current study, we explored this navigational process in the Australian desert ant Melophorus bagoti, a species living in areas with many landmarks (buildings, trees and bushes) which could help guide these ants after being moved off their normal route. Each time a forager reached a feeder and picked up some food, we moved them to another location 45º, 90º, 135º, or 180º away from the nest-feeder path and then allowed them to return home. Before releasing each forager, we tested their homeward heading in a uniform arena designed to block the surrounding landmarks and only allow ants to rely on path integration to navigate. The purpose of this test was to see how quickly and the degree to which their path integration system changed or calibrated in response to having different outgoing and incoming trip directions.
We found that foragers learn to acclimate to teleportation quickly. After being teleported on three consecutive trips, these foragers began to choose a compromise direction between their original position and their teleported position. Furthermore, we found that these foragers continued to improve over the first ten trips ultimately reaching a plateau. The directional difference (45º, 90º, 135º, or 180º) of the outbound and inbound trips appears to affect the degree to which ants can shift to the inbound path. When the difference is small (at 45º), ants are able to shift completely to the homeward direction and many return directly home. Yet as the difference between routes increases, ants shift less, choosing compromise directions at 90º and 135º locations. When we transported the foragers 180º from the feeder route, the ants did not shift their homeward path at all. These ants will travel in the wrong direction every time they are moved 180º off outbound route even after 25 trips.
The underlying cause of the differences we find in M. bagoti when compared to C. fortis remain unknown, but it is possible that the presence of landmark cues plays a large role. M. bagoti inhabits a cluttered habitat with many landmark cues to guide them when they are moved off the outbound route, while C. fortis lives in a barren desert and must search to find the nest after being moved. The presence of landmarks during training in our study may help M. bagoti foragers find the correct homeward direction easily, resulting in larger shifts just as recognisable landmarks would help a teleported human return home from a similar trip. To further explore this question, we hope to replicate this experiment on a third desert ant species endemic to southern Spain (Cataglyphis velox) which is closely related to C. fortis yet lives in cluttered environments similar to M. bagoti.
Collett M, Collett TS, Wehner R (1999) Calibration of vector navigation in desert ants. Curr Biol 9:1031–1034
Warren WH, Rothman DB, Schnapp BH, Ericson JD (2017) Wormholes in virtual space: From cognitive maps to cognitive graphs. Cognition, 166:152-163.
Wehner R, Gallizzi K, Frei C, Vesely M (2002) Calibration processes in desert ant navigation: vector courses and systematic search. J Comp Physiol A 188:683–693.