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 food processing, material transport nest building brood care, and fighting. Despite this functional diversity, mandible motion is typically thought to be constrained to rotation about a single fixed axis. 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: <i>Atta vollenweideri</i> leaf-cutter ants. Mandible movements from live restrained ants were reconstructed in three dimensions using a multi-camera rig. Rigid body kinematic analyses revealed strong evidence that mandible movement occupies a kinematic space that requires more than one rotational degree of freedom: at large opening angles, mandible motion is dominated by yaw. But at small opening angles, mandibles both 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 the 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’.

昆虫下颚（mandibles）可执行多种功能任务，涵盖食物加工、物料转运、巢穴构筑、育幼抚育与争斗行为。尽管下颚具备如此丰富的功能多样性，学界此前普遍认为其运动仅被限制为绕单一固定轴的旋转。本研究针对一类下颚功能需求广泛的切叶蚁物种——沃氏切叶蚁（Atta vollenweideri），对这一‘铰链关节假说（hinge joint hypothesis）’开展了直接定量检验。研究团队借助多相机成像系统，对被固定的活体蚂蚁的下颚运动进行了三维重构。刚体运动学分析结果提供了强有力的证据，表明下颚运动的运动学空间需要不止一个旋转自由度：当下颚张开角度较大时，其运动以偏航（yaw）为主；而当张开角度较小时，下颚会同时发生偏航与俯仰（pitch）运动。偏航与俯仰的组合可使下颚实现‘交叉错位’：当下颚闭合时，任意一侧下颚均可处于上方。研究人员在自由切割食物的蚂蚁中观察到了此类交叉错位行为，提示其具备重要的功能意义。结合近期关于其他昆虫关节连接多样性的研究报道，本研究结果表明，昆虫下颚的运动学特征远比传统认知更为多样，因此值得开展进一步的深入细致研究。本文隶属于‘动物的食物加工与营养同化’专题专栏。