title: Role of stag beetle jaw bending and torsion in grip on rivals.
abstract: In aggressive battles, the extremely large male stag beetle jaws have to withstand strongly elevated bite forces. We found several adaptations of the male Cyclommatus metallifer jaw morphology for enhanced robustness that conspecific females lack. As a result, males improve their grip on opponents and they maintain their safety factor (5.2-7.2) at the same level as that of females (6.8), despite their strongly elevated bite muscle force (3.9 times stronger). Males have a higher second moment of area and torsion constant than females, owing to an enhanced cross-sectional area and shape. These parameters also increase faster with increasing bending moment towards the jaw base in males than in females. Male jaws are more bending resistant against the bite reaction force than against perpendicular forces (which remain lower in battles). Because of the triangular cross section of the male jaw base, it twists more easily than it bends. This torsional flexibility creates a safety system against overload that, at the same time, secures a firm grip on rivals. We found no structural mechanical function of the large teeth halfway along the male jaws. Therefore, it appears that the main purpose of these teeth is a further improvement of grip on rivals.
authors.affiliation: Laboratory of Functional Morphology, University of Antwerp, Universiteitsplein 1, Antwerp 2610, Belgium Laboratory of Biophysics and Biomedical Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium jana.goyens@uantwerpen.be.
authors.forename: Jana
authors.initials: J
authors.lastname: Goyens
authors.affiliation: Laboratory of Biophysics and Biomedical Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
authors.forename: Joris
authors.initials: J
authors.lastname: Dirckx
authors.affiliation: Laboratory of Biophysics and Biomedical Physics, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.
authors.forename: Maxim
authors.initials: M
authors.lastname: Piessen
authors.affiliation: Laboratory of Functional Morphology, University of Antwerp, Universiteitsplein 1, Antwerp 2610, Belgium Department of Movement and Sport Sciences, Ghent University, Watersportlaan 2, Ghent 9000, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Aerts
mesh_terms: D000818:Animals; D001732:Bite Force; D001517:Coleoptera / Q000033:anatomy & histology / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D007568:Jaw / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male
keywords: Cyclommatus metallifer; Lucanidae; bite force; local buckling; safety factor