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.

在攻击性打斗中，体型硕大的雄性锹形虫大颚必须承受大幅提升的咬合力。我们发现雄性金属圆锹（Cyclommatus metallifer）的大颚形态存在多项针对结构强度优化的适应性特征，而同种雌性并不具备此类特征。尽管雄性的咬肌力量提升了3.9倍，但其对对手的夹持能力得到增强，且安全系数（5.2~7.2）维持在了与雌性（6.8）相当的水平。由于横截面面积更大、截面形状更优化，雄性大颚的截面二次矩与扭转常数均高于雌性。随着向大颚基部靠近的弯矩不断增大，雄性的上述参数增长速率也快于雌性。相较于垂直作用力（打斗中该力始终处于较低水平），雄性大颚对抗咬反作用力的抗弯曲性能更强。由于雄性大颚基部呈三角形截面，其相较于弯曲而言更容易发生扭转。这种扭转柔性构建了一套过载防护机制，同时能够确保对对手形成稳固夹持。我们未发现雄性大颚中部的大型齿突具备结构力学功能，因此推测这类齿突的主要作用是进一步提升对对手的夹持能力。