title: Jaw morphology and fighting forces in stag beetles.
abstract: The jaws of different species of stag beetles show a large variety of shapes and sizes. The male jaws are used as weapons in fights, and they may exert a very forceful bite in some species. We investigated in 16 species whether and how the forcefulness of their bite is reflected in their jaw morphology. We found a large range of maximal muscle forces (1.8-33 N; factor of 18). Species investing in large bite muscles also have disproportionately large jaw volumes. They use this additional jaw volume to elongate their jaws, increasing their chances of winning in battles. The fact that this also decreases the mechanical advantage is largely compensated for by elongated in-levers. As a result, high muscle forces are correlated with elevated bite forces (0.27-7.6 N; factor of 28). Despite the large difference in the forcefulness of their bite, all investigated species experience similar Von Mises stresses in their jaws while biting (29-114 MPa; factor of 4.0; calculated with finite element simulations). Hence, stag beetles have successfully adapted their jaw anatomy according to their bite force in fights.
authors.affiliation: University of Antwerp, Laboratory of Functional Morphology, Universiteitsplein 1, Antwerp 2610, Belgium University of Antwerp, Laboratory of Biophysics and BioMedical Physics, Groenenborgerlaan 171, Antwerp 2020, Belgium jana.goyens@uantwerpen.be.
authors.forename: Jana
authors.identifier: http://orcid.org/0000-0003-0176-884X
authors.initials: J
authors.lastname: Goyens
authors.affiliation: University of Antwerp, Laboratory of Biophysics and BioMedical Physics, Groenenborgerlaan 171, Antwerp 2020, Belgium.
authors.forename: Joris
authors.initials: J
authors.lastname: Dirckx
authors.affiliation: University of Antwerp, Laboratory of Functional Morphology, Universiteitsplein 1, Antwerp 2610, Belgium Ghent University, Department of Movement and Sport Sciences, Watersportlaan 2, Ghent 2000, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Aerts
keywords: Animal weaponry; Bite force; Finite element analysis; Jaw length; Lucanidae; Mechanical advantage