Data - raw_data_physical_model from Three-dimensional kinematics of leaf-cutter ant mandibles: not all dicondylic joints are simple hinges

Insects use their mandibles for a variety of tasks, including cutting and material transport, defence, building nests, caring for brood and competing for mates. Despite this functional diversity, mandible motion is thought to be constrained to rotation about a single fixed axis in the majority of extant species. Here, we conduct a direct quantitative test of this ‘hinge joint hypothesis’ in a species that uses its mandibles for a wide range of tasks: Atta vollenweideri leaf-cutter ants. Mandible movements from live restrained ants were reconstructed in three-dimensional using a multi-camera rig. Rigid body kinematic analyses revealed strong evidence that mandible movement occupies a kinematic space which requires more than one rotational degree of freedom: at large opening angles, mandible motion is dominated by yaw. But at small opening angles, mandibles yaw and pitch. The combination of yaw and pitch allows mandibles to ‘criss-cross’: either mandible can be on top when mandibles are closed. We observed criss-crossing in freely cutting ants, suggesting that it is functionally important. Combined with recent reports on diversity of joint articulations in other insects, our results show that insect mandible kinematics are more diverse than traditionally assumed, and thus worthy of further detailed investigation.This article is part of the theme issue ‘Food processing and nutrition assimilation in animals’.

昆虫上颚(mandibles)承担着多种功能，涵盖切割、物料搬运、防御、筑巢、抚育子代以及求偶竞争。尽管功能多样，学界普遍认为，绝大多数现存昆虫的上颚运动仅被限制在绕单一固定轴的旋转范围内。本研究针对这一"铰链关节假说(hinge joint hypothesis)"，选取上颚功能多样的沃氏切叶蚁（Atta vollenweideri）开展了直接的定量验证。研究团队通过多相机成像装置，对被固定的活体切叶蚁的上颚运动进行了三维重建。刚体运动学(rigid body kinematic)分析结果显示，强有力的证据表明，上颚运动所处的运动学空间需要不止一个旋转自由度(rotational degree of freedom)：当开口角度较大时，上颚运动以偏航(yaw)为主；而当开口角度较小时，上颚会同时发生偏航与俯仰(pitch)运动。偏航与俯仰的组合运动可使上颚实现"交叉闭合"：当上颚闭合时，任意一侧的上颚均可处于上方。研究团队在自由切割状态的切叶蚁中观察到了这种交叉闭合行为，表明其具有重要的功能意义。结合近期关于其他昆虫关节连接结构多样性的研究报道，本研究结果表明，昆虫上颚的运动学特征比学界以往认为的更为多样，因此值得开展进一步的深入研究。本文属于"动物的食物加工与营养吸收"专题栏目的一部分。