Elsevier

Animal Behaviour

Volume 106, August 2015, Pages 99-105
Animal Behaviour

Desert ants use olfactory scenes for navigation

https://doi.org/10.1016/j.anbehav.2015.04.029Get rights and content

Highlights

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    The uncluttered desert provides odour features that might be used for navigation.

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    Ants take consistent paths that enable them to learn spatial odour information.

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    Desert ants can follow a route that is defined only by odour information.

Desert ants, Cataglyphis fortis, forage for dead arthropods in the Tunisian salt pans. Both the unpredictable food distribution and the high surface temperatures might account for the fact that the ants do not use any pheromone trails. However, Cataglyphis has been shown to still use olfactory cues for navigation. For instance, the ants locate sparsely distributed food or pinpoint their inconspicuous nest entrance by following odour plumes. In this study we found that, as well as using odours to pinpoint a target, the ants might use environmental odours as olfactory landmarks when following habitual routes. When analysing odours collected at 100 positions in the desert, we found spatially distinct gradients of a range of different environmental odorants. Furthermore we confirm that individual foragers followed forager-specific routes when leaving the nest. Therefore these ants could potentially learn such olfactory landscape features along their stable routes. We, hence, asked whether ants could learn and use olfactory cues for route guidance. We trained ants to visit a stable feeder and presented them with a sequence of four different odours along the way. Homing ants that had already passed the odour alley on their way back were displaced to a remote test field and released at the starting point of an identical alley. Control ants that experienced the alley only during the test situation focused their search on the release point. Ants that had experienced the odours during training, however, biased their nest search towards the odour alley and performed straight walking segments along the alley. Hence, we found that ants learnt the olfactory cues along their homeward route and used these cues in the absence of other navigational information. Hence, desert ants seem to be able to use odour information to follow routes.

Section snippets

Chemical Environment

To study the ants' chemical environment we collected odour samples in their natural foraging area in the Tunisian salt pan. The salt pan near the village of Menzel Chaker (34°96′N, 10°41′E) is mainly devoid of vegetation and is a rather homogeneous habitat, although the flat ground has some structure, i.e. the salt crust can be interrupted by clefts, sandy areas or small pieces of wood or halophytic plants. A 100 m × 100 m grid was established using strings fixed with nails (mesh width, 10 m) and

The Desert Environment Provides Odour Information

For the eight environmental odours that we selected from the 100 samples, we found place-specific concentration gradients (Fig. 1) within the ants' foraging area. We can thus say that the environment provides olfactory information that could potentially be used for route navigation.

Ants Take Consistent Paths Through the Uncluttered Terrain

To use place-specific odours for navigation requires that a navigating subject repeatedly passes a place such that it can form an association between place and place-specific odour. We therefore asked whether ants

Discussion

In ants the use of olfactory cues for guidance is well documented regarding the utilization of pheromone trails laid by conspecifics (see e.g. Czaczkes et al., 2015, Steck, 2012 and references therein). However, what is less clear is whether ants might be able to learn and use environmental odour cues for route navigation. Our investigation addressed three questions related to the use of environmental odours. (1) Does the desert environment provide stable odour features that might provide route

Acknowledgments

This study was supported financially by the Max Planck Society and the Swiss National Science Foundation (SNSF). We thank G. Lutze, T. Retzke, R. Huber, I. Liebetrau and B. De Villiers for help in the field, K. Weniger for assistance with the chemical measurements, M. Reichelt for an introduction to DataTrans, E. Eilers for introducing the PDMS odour collection method and D. Veit for technical assistance. We are also grateful to A. Wystrach for providing a Matlab script for visualization of the

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