Calibration processes in desert ant navigation: vector courses and systematic search

This study investigates the ability of desert ants to adapt their path integration system to an "open-jaw" training paradigm, in which the point of arrival (from the nest) does not coincide with the point of departure (to the nest). Upon departure the ants first run off their home vector and then start a systematic search for the nest. Even if they are subjected to this training-around-a-circuit procedure for more than 50 times in succession, they never adopt straight homeward courses towards the nest. Their path integration vector gets slightly recalibrated (pointing a bit closer to the nest), and their search pattern gets asymmetric (with its search density peak shifted towards the nest), but the bipartite structure of the inbound trajectory invariably remains. These results suggest (1). that the ants cannot learn separate inbound and outbound vectors (i.e. vectors that are not 180 degrees reversals of each other), (2). that the recalibrated vector is dominated by the ant's outbound course, (3). that the recalibration of the vector and the modification of the search geometry are fast and flexible processes occurring whenever the ant experiences a mismatch between the stored and actual states of its path integrator.

Lateral optic flow does not influence distance estimation in the desert ant Cataglyphis fortis

The present account answers the question of whether desert ants (Cataglyphis fortis) gauge the distance they have travelled by using self-induced lateral optic-flow parameters, as has been described for bees. The ants were trained to run to a distant food source within a channel whose walls were covered with black-and-white gratings. From the food source, they were transferred to test channels of double or half the training width, and the distance they travelled before searching for home and their walking speeds were recorded. Since the animals experience different motion parallax cues when walking in the broader or narrower channels, the optic-flow hypothesis predicted that the ants would walk faster and further in the broader channels, but more slowly and less far in the narrower channels. In contrast to this expectation, neither the walking speeds nor the searching distances depended on the width or height of the channels or on the pattern wavelengths. Even when ventral-field visual cues were excluded by covering the eyes with light-tight paint, the ants were not influenced by lateral optic flow-field cues. Hence, walking desert ants do not depend on self-induced visual flow-field cues in gauging the distance they have travelled, as do flying honeybees, but can measure locomotor distance exclusively by idiothetic means.