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First published online May 1, 2009
Journal of Experimental Biology 212, 1528-1534 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.027961

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Desert ants do not rely on sky compass information for the perception of inclined path segments

Doreen Heß, Julja Koch and Bernhard Ronacher^*

Humboldt-Universität zu Berlin, Department of Biology, Invalidenstraße 43, D 10115 Berlin, Germany

^* Author for correspondence (e-mail: bernhard.ronacher{at}rz.hu-berlin.de)

Accepted 19 February 2009

On their foraging excursions, desert ants (Cataglyphis fortis) navigate by means of path integration, exhibiting high precision even in undulating terrain. To avoid errors in their home vector the ants must measure the slopes of ascents and descents in their itinerary. This information is necessary to convert the distances actually walked on the slopes into the ground distance, which is the crucial parameter for vector navigation. However, it is as yet unknown how Cataglyphis perceives the slopes of inclines. We asked whether the ants gauge slopes by means of the changes in the sky's polarization pattern or the sun's position imposed by the unusual head posture when walking on inclines. During training on a ramp, we manipulated the sky compass cues available for the ants. If both sky compass cues, polarization pattern and sun position, were excluded during ramp training, the ants behaved in subsequent tests as if they had never encountered a slope. However, the presence of either of the two compass cues was sufficient for the ants to memorize the sloped path segment. In a third experiment, the supposed polarization cue was excluded by covering the training and test channels with a linear polarization filter. In these tests the ants clearly showed that they had perceived and memorized an ascent also without a change in the polarization pattern. Hence, changes in polarization perception can be ruled out as the crucial cue for gauging slopes, and we conclude that slopes are monitored by a, still unknown, proprioceptive mechanism.

Key words: Cataglyphis, ants, path integration, vector navigation, 3-D orientation, Hymenoptera

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