The use of clamping grips and friction pads by tree frogs for climbing curved surfaces

Endlein, T., Ji, A., Yuan, S., Hill, I., Wang, H., Barnes, W. J. P., Dai, Z. and Sitti, M. (2017) The use of clamping grips and friction pads by tree frogs for climbing curved surfaces. Proceedings of the Royal Society of London Series B: Biological Sciences, 284(1849), 20162867. (doi: 10.1098/rspb.2016.2867) (PMID:28228509)

Abstract

Most studies on the adhesive mechanisms of climbing animals have addressed attachment against flat surfaces, yet many animals can climb highly curved surfaces, like twigs and small branches. Here we investigated whether tree frogs use a clamping grip by recording the ground reaction forces on a cylindrical object with either a smooth or anti-adhesive, rough surface. Furthermore, we measured the contact area of fore and hindlimbs against differently sized transparent cylinders and the forces of individual pads and subarticular tubercles in restrained animals. Our study revealed that frogs use friction and normal forces of roughly a similar magnitude for holding on to cylindrical objects. When challenged with climbing a non-adhesive surface, the compressive forces between opposite legs nearly doubled, indicating a stronger clamping grip. In contrast to climbing flat surfaces, frogs increased the contact area on all limbs by engaging not just adhesive pads but also subarticular tubercles on curved surfaces. Our force measurements showed that tubercles can withstand larger shear stresses than pads. SEM images of tubercles revealed a similar structure to that of toe pads including the presence of nanopillars, though channels surrounding epithelial cells were less pronounced. The tubercles' smaller size, proximal location on the toes and shallow cells make them probably less prone to buckling and thus ideal for gripping curved surfaces.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Endlein, Dr Thomas and Hill, Mr Iain and Barnes, Dr William
• Authors: Endlein, T., Ji, A., Yuan, S., Hill, I., Wang, H., Barnes, W. J. P., Dai, Z., and Sitti, M.
• College/School: College of Medical Veterinary and Life Sciences > School of Molecular Biosciences; College of Medical Veterinary and Life Sciences > School of Biodiversity, One Health & Veterinary Medicine
• Journal Name: Proceedings of the Royal Society of London Series B: Biological Sciences
• Publisher: The Royal Society
• ISSN: 0962-8452
• ISSN (Online): 1471-2954
• Copyright Holders: Copyright © 2017 The Authors
• First Published: First published in Proceedings of the Royal Society of London Series B: Biological Sciences 284(1849):20162867
• Publisher Policy: Reproduced under a Creative Commons License