Snap-jaw morphology is specialized for high-speed power amplification in the Dracula ant, Mystrium camillae

What is the limit of animal speed and what mechanisms produce the fastest movements? More than natural history trivia, the answer provides key insight into the form-function relationship of musculoskeletal movement and can determine the outcome of predator-prey interactions. The fastest known animal movements belong to arthropods, including trap-jaw ants, mantis shrimp, and froghoppers, that have incorporated latches and springs into their appendage systems to overcome the limits of muscle power. In contrast to these examples of power amplification, where separate structures act as latch and spring to accelerate an appendage, some animals use a “snap-jaw” mechanism that incorporates the latch and spring on the accelerating appendage itself. We examined the kinematics and functional morphology of the Dracula ant, Mystrium camillae, who use a snap-jaw mechanism to quickly slide their mandibles across each other similar to a finger snap. Kinematic analysis of high-speed video revealed that snap-jaw ant mandibles complete their strike in as little as 23 μsec and reaching peak velocities of 90 m s-1, making them the fastest known animal appendage. Finite element analysis demonstrated that snap-jaw mandibles were less stiff than biting non-power-amplified mandibles, consistent with their use as a flexible spring. These results extend our understanding of animal speed and demonstrate how small changes in morphology can result in dramatic differences in performance.

动物运动速度的极限究竟为何？又是何种机制催生了最快的动物运动？该问题的答案绝非单纯的自然史趣闻，其可为肌肉骨骼运动的形态-功能关系提供关键洞见，亦能阐释捕食者与猎物间相互作用的最终结果。目前已知最快的动物运动行为均属于节肢动物，包括陷阱颚蚁（trap-jaw ants）、螳螂虾（mantis shrimp）与沫蝉（froghoppers），这类类群通过在附肢系统中整合锁扣与弹簧结构，突破了肌肉功率的极限。与这类通过独立结构分别充当锁扣与弹簧来实现附肢加速的功率放大机制不同，部分动物采用了‘弹颚’（snap-jaw）机制，将锁扣与弹簧整合于加速附肢自身之上。本研究针对德古拉蚁（Dracula ant，*Mystrium camillae*）开展运动学与功能形态学分析，该类群借助弹颚机制，使其下颚快速相互滑动，类似人类打响指的动作。高速录像的运动学分析结果显示，弹颚蚁的下颚完成攻击仅需短短23微秒，峰值速度可达90米每秒，使其成为目前已知运动速度最快的动物附肢。有限元分析（finite element analysis）结果表明，弹颚蚁的下颚刚度低于未采用功率放大机制的啃食用下颚，这与其作为柔性弹簧的功能属性相符。本研究结果拓展了学界对动物运动速度的认知，并阐明了形态学上的微小改变如何能带来运动性能的巨大差异。