Slippery Surfaces and the Biomechanics of Climbing in Macaranga-Ant Mutualisms

This thesis has three data-driven chapters, an introduction, a general methods section and a discussion. The first of the data chapters shows that claws are the essential attachment device used by wax runner ants to climb their host Macaranga trees. When wax runners had their claw tips ablated, they could no longer climb on the slippery epicuticular wax crystals of Macaranga, but they could still climb on artificial smooth surfaces. When wax runners had their arolia ablated, they could still climb the slippery epicuticular wax crystals of Macaranga, but they could not climb artificial smooth surfaces. This showed that claws are essential for wax running and arolia are essential for climbing smooth artificial surfaces. The second data chapter measures the thickness of the epicuticular wax crystal layer as it regenerates, synchronised with climbing tests on the Macaranga stem surface. These combined measurements showed that when the wax crystals are removed, there are open sections of epidermis that ant arolia can attach to allowing them to climb. On the day that the epicuticular wax crystals are removed, generalist ants can climb trees that were previously too slippery for them to ascend. As the wax regenerates it covers the surface, interrupting the adhesion of the arolia on the epidermis. At four days of wax regeneration, the surface is at its slipperiest. The surface is completely covered by epicuticular wax crystals preventing the adhesion of arolia, but the crystal mat is still very thin and fragile. So, while ant claws can penetrate the wax crystal layer, it is not thick or sturdy enough to support the ants’ weight until it has had longer to regenerate. The third data chapter measures the forces produced by a single wax runner ant foot dragged across a waxy Macaranga stem surface. The experiment was done with three different quantities of epicuticular wax crystals on the stem: wax wiped off, four days of wax regeneration, and the untouched state. The data show that the quantity of epicuticular wax crystal on the surface has a significant influence on the forces produced by the ant foot as it was dragged over the stem surface. However, further experiments would be needed to determine the precise nature of the influence of the wax on forces produced. The discussion summarises these findings and their implications for our understanding of the phenomena of wax running. It also introduces a metaphor with human climbing that could lead to interesting new research directions.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Brechka, Patrick

Advisor dc:contributor.advisor

• Federle, Walter

• Ants
• Biomechanics
• Climbing
• Crematogaster
• Macaranga
• Trees

Licence

• https://www.repository.cam.ac.uk/bitstreams/059dfa3a-11f5-4e05-b2d6-13dfd3a52fb1/download
• https://creativecommons.org/licenses/by-sa/4.0/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.113838

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/376724