Data from: Role of stag beetle jaw bending and torsion in grip on rivals

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.

在激烈的打斗场景中，巨型雄性锹形虫的大颚需要承受大幅升高的咬合力。我们发现，雄性金属锯锹形虫（Cyclommatus metallifer）的颚部形态存在多项适应性特征，以提升结构鲁棒性，而这些特征为同种雌性所不具备。尽管雄性的咬肌力量较雌性提升了3.9倍，但其对对手的咬合夹持能力得到增强，且安全系数（safety factor）维持在5.2–7.2的水平，与雌性的6.8基本相当。得益于更大的截面积与更优化的截面形状，雄性颚部的面积二次矩（second moment of area）与扭转常数（torsion constant）均高于雌性；且相较于雌性，雄性的上述参数随颚基部弯矩的提升增长速率更快。雄性颚部对抗咬反作用力的抗弯曲性能优于对抗垂直作用力（打斗中垂直作用力水平更低）。由于雄性颚基部呈三角形截面，其扭转刚度低于弯曲刚度，这种扭转柔性构建了一套过载防护系统，同时可确保对对手的稳固夹持。我们未发现雄性颚部中段的大型齿突具备结构力学功能，由此推测，这类齿突的核心作用是进一步提升对对手的夹持能力。