title: Finite-element modelling reveals force modulation of jaw adductors in stag beetles.
abstract: Male stag beetles carry large and heavy mandibles that arose through sexual selection over mating rights. Although the mandibles of Cyclommatus metallifer males are used in pugnacious fights, they are surprisingly slender. Our bite force measurements show a muscle force reduction of 18% for tip biting when compared with bites with the teeth located halfway along the mandibles. This suggests a behavioural adaptation to prevent failure. We confirmed this by constructing finite-element (FE) models that mimic both natural bite situations as well as the hypothetical situation of tip biting without muscle force modulation. These models, based on micro-CT images, investigate the material stresses in the mandibles for different combinations of bite location and muscle force. Young's modulus of the cuticle was experimentally determined to be 5.1 GPa with the double indentation method, and the model was validated by digital image correlation on living beetles. FE analysis proves to be a valuable tool in the investigation of the trade-offs of (animal) weapon morphology and usage. Furthermore, the demonstrated bite force modulation in male stag beetles suggests the presence of mechanosensors inside the armature.
authors.affiliation: Laboratory of Functional Morphology, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium Laboratory of BioMedical Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium jana.goyens@uantwerpen.be.
authors.forename: J
authors.initials: J
authors.lastname: Goyens
authors.affiliation: Laboratory of BioMedical Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Soons
authors.affiliation: Laboratory of Functional Morphology, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium Department of Movement and Sport Sciences, Ghent University, Watersportlaan 2, 9000 Ghent, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Aerts
authors.affiliation: Laboratory of BioMedical Physics, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Dirckx
mesh_terms: D000818:Animals; D001517:Coleoptera / Q000502:physiology*; D005260:Female; D020342:Finite Element Analysis; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging / Q000502:physiology*; D008954:Models, Biological; D055114:X-Ray Microtomography
keywords: Lucanidae; Poisson ratio; Young's modulus; bite force; digital image correlation; failure strength