In this white house, we investigate the orientation of animals when we locally reverse the polarity of the Earth's magnetic field with a weak electromagnet custom built for biological investigations. The white tarp serves to obstruct the use of landmarks as orientation cues.
We investigate compasses in homing leaf-cutter ants
and migrating butterflies!
Please see our publications on this subject:
Banks, A. N. and R. B. Srygley (2003) Orientation by magnetic field in leaf-cutter ants, Atta colombica (Hymenoptera: Formicidae). Ethology 109: 835-846.
Abstract. Leaf-cutter ants (Atta colombica) use trail following to travel between foraging sites and the home nest. However, this combination of pheromone and visual cues is likely to be complemented by a directional reference system such as a compass, used not only when foraging but also during colony formation, where foraging trails degrade or where ants become displaced. One candidate system is the magnetic polarity compass. We tested the orientation of leaf-cutter ants under a magnetic field of reversed polarity, with the prediction that the ants would show 180 degrees deflection compared with control ants in an unchanged geomagnetic field. When the sunıs disc was unobstructed by clouds, orientation was the same as that of control ants, implying that magnetic cues were not used to orient. However, when the sky was overcast, ants in the experimental treatment significantly shifted their mean orientation both in comparison to controls and reversed polarity ants under sun. Although a total reversal in orientation was not induced, the results nonetheless demonstrate that Atta respond to magnetic reversal in the absence of sunlight cues, and suggest a role for magnetic cues in determining direction during orientation.
You may download this manuscript as an Adobe Acrobat PDF file.
Riveros, A. J. and R. B. Srygley (2008) Do leaf-cutter ants Atta colombica orient their path-integrated home vector with a magnetic compass? Animal Behaviour 75: 1273-1281.
Abstract. Leaf-cutter ants, Atta colombica, forage over 250 m in structurally-complex, Neotropical rainforests that occlude sun or polarized light cues. Night foraging makes the use of celestial cues and landmarks all the more difficult. We investigated the directional cues used by leaf-cutter ants to orient homeward by experimentally reversing the polarity of the local magnetic field and by experimentally subjecting the ants to a strong magnetic pulse to disrupt a magnetic compass. In both experiments, we transferred homeward-bound ants from a foraging trail to a table in a chamber that occluded landmark and celestial cues. In both experiments, control ants showed path integration and walked directly towards the nest. In the reversed field, one-half of the experimental ants oriented according to the reversed field (geographically 180° opposite to the nestıs direction), indicating that they used a magnetic compass to update their positional reference derived from path integration. The other half walked towards the nest, suggesting that they may have used an egocentric reference to measure their rotation when displaced, although other explanations have not been entirely excluded. With application of a very brief, but strong, magnetic pulse, experimental ants oriented randomly. We conclude that the leafcutter ants use the earthıs magnetic field as a reference by which to orient when path-integrating towards home.
You may download this manuscript as an Adobe Acrobat PDF file.
Department of Zoology University of Oxford South Parks Road
Oxford OX1 3PS England
Email -- bob.srygley@ zoo.ox.ac.uk
Web -- http://users.ox.ac.uk/~zool0206/
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Abstract. Leaf-cutter ants (Atta colombica) use trail following to travel between foraging sites and the home nest. However, this combination of pheromone and visual cues is likely to be complemented by a directional reference system such as a compass, used not only when foraging but also during colony formation, where foraging trails degrade or where ants become displaced. One candidate system is the magnetic polarity compass. We tested the orientation of leaf-cutter ants under a magnetic field of reversed polarity, with the prediction that the ants would show 180 degrees deflection compared with control ants in an unchanged geomagnetic field. When the sunıs disc was unobstructed by clouds, orientation was the same as that of control ants, implying that magnetic cues were not used to orient. However, when the sky was overcast, ants in the experimental treatment significantly shifted their mean orientation both in comparison to controls and reversed polarity ants under sun. Although a total reversal in orientation was not induced, the results nonetheless demonstrate that Atta respond to magnetic reversal in the absence of sunlight cues, and suggest a role for magnetic cues in determining direction during orientation.
Abstract. Leaf-cutter ants, Atta colombica, forage over 250 m in structurally-complex, Neotropical rainforests that occlude sun or polarized light cues. Night foraging makes the use of celestial cues and landmarks all the more difficult. We investigated the directional cues used by leaf-cutter ants to orient homeward by experimentally reversing the polarity of the local magnetic field and by experimentally subjecting the ants to a strong magnetic pulse to disrupt a magnetic compass. In both experiments, we transferred homeward-bound ants from a foraging trail to a table in a chamber that occluded landmark and celestial cues. In both experiments, control ants showed path integration and walked directly towards the nest. In the reversed field, one-half of the experimental ants oriented according to the reversed field (geographically 180° opposite to the nestıs direction), indicating that they used a magnetic compass to update their positional reference derived from path integration. The other half walked towards the nest, suggesting that they may have used an egocentric reference to measure their rotation when displaced, although other explanations have not been entirely excluded. With application of a very brief, but strong, magnetic pulse, experimental ants oriented randomly. We conclude that the leafcutter ants use the earthıs magnetic field as a reference by which to orient when path-integrating towards home.
Sponsored by the National Geographic Society
Robert B. SrygleyDepartment of Zoology University of Oxford South Parks Road
Oxford OX1 3PS England
Email -- bob.srygley@ zoo.ox.ac.uk
Web -- http://users.ox.ac.uk/~zool0206/
Return to home page