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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

View larger version (9K): [in this window] [in a new window]   Fig. 1. Schematic side view of the setup used in experiment 1. Three different training channels: (Ai) open ramp training with open view of the sky; (Aii) closed ramp training with ramp covered with orange Perspex and cardboard shield, no sky compass cues available on the ramp; (Aiii) flat training with open view of the sky, except for a short segment that was covered with orange Perspex and cardboard shield (see pictograms). (B) Schematic drawing of the test channel system with four options for a descent. N, nest: F, feeder; R, release point; POL, polarization. Dimensions in meters. The angle of the ascent was 70 deg.

View larger version (11K): [in this window] [in a new window]   Fig. 2. (A) Schematic drawing of the training channels used for experiment 2 (`hill' training). (B) Side view of the test channels. (i) Unimpeded view of the sky (except for the restrictions imposed by the channel's side walls); (ii) blocking of the sky's POL pattern (via orange Perspex) with view of the sun still possible; (iii) access to the POL pattern but blocking of the sun by means of a cardboard shield; (iv) complete blocking of sky compass information (via orange Perspex and exclusion of direct view of the sun); and (v) as a control, a fifth group of ants underwent a flat training with open view of the sky, except for a 1.37 m segment covered with orange Perspex. N, nest: F, feeder; R, release point; POL, polarization. Dimensions in meters. The angle of the ascent was 70 deg.

View larger version (9K): [in this window] [in a new window]   Fig. 3. (A) Training channels used in experiment 3: (i) flat training and (ii) ramp training. Broken line over the channel indicates cover with POL filter transparency. The test channel had the same dimensions as shown in ii and was laid in parallel to the training channel at a distance of 10 cm. Ants could be guided individually into the test channel via a switch. (B) Transmission of the POL filter in the UV range of the spectrum. Note the near zero curve for crossed filters, demonstrating high filter quality. N, nest: F, feeder; R, release point; POL, polarization. Dimensions in meters. The angle of the ascent was 70 deg.

View larger version (6K): [in this window] [in a new window]   Fig. 4. Proportion of complete and incomplete descents (i.e. rejections of the ramp) after ramp training. Ants that had no sky compass cues while on the ramp (ii) behaved like ants after flat training (iii). The drawing on the right gives a simplified sketch of the training conditions (for details, see Fig. 1). Proportions of incomplete versus complete descents in ii and iii were not significantly different; however, both were different from i (P0.001). Pol, polarization.

View larger version (25K): [in this window] [in a new window]   Fig. 5. Results of ascent and descent tests after hill training. (A) Proportions of complete versus incomplete ascents; (C) proportions of complete versus incomplete descents; (B,D) ascent and descent heights, respectively. Different training conditions are indicated in the sketches between A and C, for details of the training see Fig. 2. The proportions of complete versus incomplete ascents in A were not significantly different between training i,ii,iii (P>0.2; 2 test) and were not significantly different between training iv and v (P=0.18; Fisher's exact test). However, i–iii versus iv and v differed highly significantly (P<0.001). (B) A similar picture was found for the ascent heights using the Games–Howell post-hoc test: i–iii, P>0.7; iv compared with v, P=0.03; however, P=0.14 if the complete ascents were not considered. i–iii versus iv and v, P=0.003. (C) Proportions of complete and incomplete descents. i–iii, P=0.38; iv versus v, P>0.7; i–iii versus iv and v, P<0.0001. (D) Descent heights. i–iii, P>0.7; iv versus v, P>0.8; i–iii versus iv and v, P<0.0001. Closed circles, outliers.

View larger version (8K): [in this window] [in a new window]   Fig. 6. Results of training under a linear POL (polarization) filter, i.e. with a single e-vector direction, and under the exclusion of the direct view of the sun. After flat training (i) the ants refused to climb on the ramp, contrary to the expectation of the POL hypothesis whereas they readily accepted the ramp after ramp training (ii); i versus ii, P<0.0001.

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