Mechanical and elemental characterization of ant mandible cuticle and their consequences for bite mechanics

• Applicant: Dr. Cristian Luan Klunk
• Subject Area: Systematics and Morphology (Zoology)
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541551257

Mandibles are the predominant tools employed by ant workers to perform colony non-reproductive tasks, from subtle activities like moving the brood through processing food to powerful defensive bites. This multitask characteristic should have had relevant consequences for the mandible morphological evolution. Besides the effects of mandible morphology, it is known for a few leaf-cutting ants that the accumulation of transition metals like Zn along the masticatory margin cuticle increases its hardness and resistance to wear. However, other mandibular regions are also heavily demanded during a bite, like the mandibular articulations with the head, whose specific material properties have rarely been measured in ants before. A relevant aspect of bite mechanics is bite force. There is evidence that ant workers can vary inter- and intraspecifically in bite forces, but how this variation reflects the mechanical responses of mandibles to bite loading is still poorly explored for ants. Within this proposal, I aim to measure the elemental composition and characterize the mechanical properties of the worker mandible cuticle of two ant species, namely Formica cunicularia and Acromyrmex sp., as well as measure their worker’s bite forces. Finally, I aim to investigate the consequences of mechanical properties and bite force variation in those mandibles under bite loading, employing biting simulations. I hypothesize that the masticatory margin has the highest values of Young’s modulus (E) and hardness (H), followed by the mandibular articulations with the head (i.e., dorsal and ventral) and the mandibular blade. Also, I expect that the variation in mechanical properties correlates with variation in element composition along the mandibular regions, especially regarding the distribution of transition metals. I will measure the cuticular H and E through nanoindentation and the element composition of the distinct mandibular region with disperse X-ray spectroscopy. Also, I will employ Confocal Laser Scanning Microscopy to evaluate the variation in cuticle sclerotization levels along the mandible. Finally, I will use a custom-built device to measure ant worker bite forces. To investigate the effects of mandibular mechanical properties variation on bite performance, I will employ Finite Element Analysis (FEA) to simulate biting conditions comparing mandibles with a homogeneous versus heterogeneous distribution of E in the defined mandibular regions. For FEA, mandibles will be rendered as 3D meshes generated with Synchrotron microcomputer tomography data. This project will significantly contribute to the realm of ant functional morphology.

• DFG Programme: Research Grants