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Dynamics of prey prehension by chameleons through viscous adhesion

Abstract

Among predators using an adhesive tongue to feed, chameleons are able to capture large prey by projecting the tongue at high acceleration. Once in contact with a prey, the tongue retracts with a comparable acceleration to bring it to the mouth. A strong adhesion between the tongue tip and the prey is therefore required during the retraction phase to ensure a successful capture. To investigate the mechanism responsible for this strong bond, the viscosity of the mucus produced at the chameleon’s tongue pad is measured, using the viscous drag exerted on rolling beads by a thin layer of mucus. Here we show that the viscosity of this secretion is about 400 times larger than that of human saliva. We incorporate this viscosity into a dynamical model for viscous adhesion, which describes the motion of the compliant tongue and the prey during the retraction phase. The variation of the maximum prey size with respect to the chameleon body length is derived, and compared with in vivo observations for various chameleon species. Our study shows that the size of the captured prey is not limited by viscous adhesion, owing to the high mucus viscosity and large contact area between the prey and the tongue.

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Figure 1: Position as a function of time of a spherical steel bead rolling down an inclined plane covered by a mucus layer of thickness hs for three specimens of Chamaeleo calyptratus.
Figure 2: Kinematics profiles for one representative capture of a cricket (mp 0.5 g) by a Chamaeleo calyptratus specimen (LSVL = 150 mm) recorded with a high-speed camera at 1,000 fps.
Figure 3: Schematic of the system and results of the dynamical model.
Figure 4: Maximum prey size versus snout vent length for various chameleons.

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Acknowledgements

The lizard specimens were provided by C. Remy (Musée d’Histoire Naturelle de Tournai). The authors acknowledge C. Gay and D. Nonclercq for fruitful discussions. A. Maillard is acknowledged for the prey capture experiments. This work was partially supported by the MECAFOOD ARC research project from UMONS. F.B. acknowledges financial support from the Government of the Region of Wallonia (REMANOS Research Programme).

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P.D. and V.B. conceived the study; P.D. designed the experiments; F.B., D.L., L.-N.Z. and V.B. carried out the experiments; F.B., D.L. and P.D. analysed the data; F.B. and P.D. developed the theoretical model; F.B. and P.D. wrote the manuscript.

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Correspondence to Pascal Damman.

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The authors declare no competing financial interests.

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Brau, F., Lanterbecq, D., Zghikh, LN. et al. Dynamics of prey prehension by chameleons through viscous adhesion. Nature Phys 12, 931–935 (2016). https://doi.org/10.1038/nphys3795

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