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.

Structure, mechanics and material properties of claw cuticle from mole cricket Gryllotalpaorientalis

“…The hollow structure has obvious advantages over solid structure in bearing loads when the total amount of the material is constant; moreover, the triangular cross-section makes the structure more bending resistant than it would have been with other cross-section (e.g. circular) [17,18]. The area ratio of the cavity on the cross section increases with the distance from the tip to end[5].…”

“…They speculated the metal elements played a role in enhancing localized hardness, abrasion resistance and fracture strength during evolutionary process[34,35]. Moreover, chemical gradients and cross-linking have been reported as another solution to enhance the mechanical properties of the organic models such as squid beak[18]. These gradients may cause variations in the optical properties of the tissues, as the dark colour in the tip of the claw.…”

Biocycle between Design and Additive Manufacturing

“…The formal layout of the bicycle is designed to go beyond the concept of a trapezoidal frame with diagonal and circular section tubulars, in order to satisfy the mechanical resistance requirements of the load‐bearing structure. Regarding the tubulars, these aspects have been pursued after the in‐depth study of the work conducted by Goyens et al., [ 5,6 ] where it emerges that the triangular section provides a higher strength than the elliptical one, due to particular loading conditions such as the “bite” of the “stag beetle.” The shapes identified in the jaw of the stag beetle ( Figure a) could help to avoid structural failure by providing a geometry that resists bending in the entire structure, with reinforcement at the end, to dissipate energy. The triangular geometry of the base (the area that receives the greatest load) increases the torsion resistance in the base even more.…”

“…www.advancedsciencenews.com www.ms-journal.de Figure 1. a) Sections (2-3) of the stag beetle jaw (1) [6] ; b) Rover Safety Bike 1885 ©Science Museum/Science and Society Picture Library.…”