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, 276 (1673), 3705-9

A New Angle on Clinging in Geckos: Incline, Not Substrate, Triggers the Deployment of the Adhesive System

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A New Angle on Clinging in Geckos: Incline, Not Substrate, Triggers the Deployment of the Adhesive System

Anthony P Russell et al. Proc Biol Sci.

Abstract

Lizards commonly climb in complex three-dimensional habitats, and gekkotans are particularly adept at doing this by using an intricate adhesive system involving setae on the ventral surface of their digits. However, it is not clear whether geckos always deploy their adhesive system, given that doing so may result in decreased (i.e. reduction in speed) locomotor performance. Here, we investigate circumstances under which the adhesive apparatus of clinging geckos becomes operative, and examine the potential trade-offs between speed and clinging. We quantify locomotor kinematics of a gecko with adhesive capabilities (Tarentola mauritanica) and one without (Eublepharis macularius). Whereas, somewhat unusually, E. macularius did not suffer a decrease in locomotor performance with an increase in incline, T. mauritanica exhibited a significant decrease in speed between the level and a 10 degrees incline. We demonstrate that this results from the combined influence of slope and the deployment of the adhesive system. All individuals kept their digits hyperextended on the level, but three of the six individuals deployed their adhesive system on the 10 degrees incline, and they exhibited the greatest decrease in velocity. The deployment of the adhesive system was dependent on incline, not surface texture (600 grit sandpaper and Plexiglas), despite slippage occurring on the level Plexiglas substrate. Our results highlight the type of sensory feedback (gravity) necessary for deployment of the adhesive system, and the trade-offs associated with adhesion.

Figures

Figure 1.
Figure 1.
The effects of incline and surface structure on gecko locomotion. (a,d) Mean velocity of E. macularius (black bars) and T. mauritanica (grey bars) running on a level, 10 and 30° surface covered with (a) 600 grit sandpaper and (d) Plexiglas. Note that for (a) and (d), dark grey bars represent the mean velocities for individuals of Tarentola that used their adhesive apparatus on the 10° incline, and cross-hatched bars represent the same for those that did not. Forty-six and 81 per cent refer to the velocities attained by those individuals of Tarentola that, respectively, employed and did not employ their adhesive apparatus on the 10° high-friction slope, expressed as a proportion of their velocities on the horizontal high-friction surface. (b,e) Mean duty factor for E. macularius (black bars) and T. mauritanica (grey bars) running on a level, 10 and 30° surface covered with (b) 600 grit sandpaper and (e) Plexiglas. (c,f) Mean stance duration for E. macularius (black bars) and T. mauritanica (grey bars) running on a level, 10 and 30° surface covered with (c) 600 grit sandpaper and (f) Plexiglas. All values are mean ± s.e. Note that E. macularius was unable to move on the inclined surfaces covered with Plexiglas.
Figure 2.
Figure 2.
Effects of incline on duration of adhesion. Mean adhesion time (% of stance) for individuals running on a 10 and 30° incline lined with 600 grit sandpaper. Surface structure did not influence these values. Values are mean ± s.e. Note that only three of the six individuals deployed their adhesive system on the 10° incline.

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