Data - raw_data_atta_vollenweider 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: Atta vollenweideri 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’.

昆虫依靠大颚（mandibles）完成诸多任务，包括食物加工、物料转运、筑巢、育幼与争斗。尽管其功能具有多样性，过往学界普遍认为，大颚的运动仅局限于绕单一固定轴的旋转。本研究针对这一“铰链关节假说（hinge joint hypothesis）”展开直接定量检验，实验对象为一类利用大颚完成广泛任务的物种：沃氏切叶蚁（Atta vollenweideri leaf-cutter ants）。研究人员借助多相机成像系统，对被约束的活体蚂蚁的大颚运动进行三维重构。刚体运动学分析（rigid body kinematic analyses）结果显示，大颚运动占据的运动学空间需要不止一个旋转自由度：当大颚张开角度较大时，其运动以偏航（yaw）为主；而当张开角度较小时，大颚同时发生偏航与俯仰（pitch）运动。偏航与俯仰的组合可使大颚实现“交叉运动”：闭合时两侧大颚可互为上下。研究人员在自由切割的蚂蚁中观察到了这种交叉运动，提示其具备重要功能意义。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，昆虫大颚的运动学特征较以往假设更为多样，因此值得开展进一步的细致研究。本文属于“动物的食物加工与营养同化（Food processing and nutrition assimilation in animals）”专题议题。