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First published online September 14, 2007
Journal of Experimental Biology 210, 3337-3343 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004473

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Orientation towards prey in antlions: efficient use of wave propagation in sand

Arnold Fertin^* and Jérôme Casas

Université de Tours, IRBI UMR CNRS 6035, Parc Grandmont, 37200 Tours, France

View larger version (32K): [in this window] [in a new window]   Fig. 1. (A) Schema of the setup to record wave propagation through sand caused by a walking ant. (B) Schema of the setup to simulate a walking ant with a electromagnetic shaker. s, sand; a, ant; mb, microphone membrane; pb, PerspexTM box; m, microphone; p, microphone preamplifier; ar, aluminium rod mounted on electromagnetic shaker; n, needle.

View larger version (89K): [in this window] [in a new window]   Fig. 2. Example of the detection algorithm of interlaced areas. See Materials and methods for further details. (A) Original frame with a close-up of an area with interlacing (boxed) in the upper left corner (contrast is enhanced for illustrative purposes). (B,C) First processing of red and green images. (D) Result of the Boolean `AND' operation between red and green images. (E) Application of the despeckle filter after detection of interlaced area. (F) Final identification of moving areas during sand tossing relative to the source of stimuli. h, antlion head, t, tip of the electromagnetic shaker, hm, interlaced area due to head movement, st, interlaced areas due to flying sand. The yellow point is the centroid of sand tossing areas.

View larger version (6K): [in this window] [in a new window]   Fig. 3. Reference frame and angle definition. 1, angle to the tip of the electromagnetic shaker; 2, angle to sand tossing area; 3, angle between tip location and sand tossing area, reflecting the precision of sand tossing.

View larger version (29K): [in this window] [in a new window]   Fig. 4. Biotest design. (A) Example of a signal recorded when an ant walks on the sand surface above the membrane of the microphone. The arrow points to the signal reproduced in B; red lines represent leg strokes. (B) A close-up of the signal identified in the recording. (C) The mean signal used for pattern recognition. This signal was derived from the mean of 20 signals randomly extracted in 15 recordings. The green envelope indicates the standard deviation. (D) Example of pattern (i.e. mean signal) recognition in the recording shown in B. The blue curve is the smoothed envelope of the normalized cross-correlation function (CCF). The signals recognized using the maximum of the normalized cross-correlation function are indicated in B and D by vertical red lines.

View larger version (7K): [in this window] [in a new window]   Fig. 5. Power spectral density comparison between the ant signal (black curve) and the electromagnetic shaker signal (pink curve).

View larger version (7K): [in this window] [in a new window]   Fig. 6. Mean proportions of bites (light grey bars) and sand tossings (dark grey bars) during attacks by non-moving (left) and moving (right) antlions. Attacks by moving antlions were divided into two parts: before and after they started to move. Values are means ± 95% CI (paired Wilcoxon signed-rank test; non-moving: N=13, V=34, P=0.4548; before movement: N=13, V=29, P=0.4961; after movement: N=13, V=9, **P<0.01). NS, non-significant.

View larger version (15K): [in this window] [in a new window]   Fig. 7. (A) Circular distribution of the precision angle of sand tossings (3). The area of each sector is proportional to its frequency. The scale is indicated on the left half of the circle. (B) Angle of sand tossings (2) as function of the angle of the tip (1). This response is linear (solid line), and close to the perfect response (dotted line) (see text for details).