Role of stag beetle jaw bending and torsion in grip on rivals
Faculty of Sciences. Biology
Faculty of Sciences. Physics
Journal of the Royal Society interface: physical and life sciences. - London
, p. 1-15
University of Antwerp
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 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, due 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 the rivals.