Larabee Fredrick J, Gronenberg Wulfila, Suarez Andrew V
Department of Entomology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA
Department of Entomology, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA.
J Exp Biol. 2017 Sep 1;220(Pt 17):3062-3071. doi: 10.1242/jeb.156513.
Trap-jaw ants are characterized by high-speed mandibles used for prey capture and defense. Power-amplified mandibles have independently evolved at least four times among ants, with each lineage using different structures as a latch, spring and trigger. We examined two species from the genus (subfamily Formicinae), whose morphology is unique among trap-jaw ant lineages, and describe the performance characteristics, spring-loading mechanism and neuronal control of strikes. Like other trap-jaw ants, latch their jaws open while the large closer muscle loads potential energy in a spring. The latch differs from other lineages and is likely formed by the co-contraction of the mandible opener and closer muscles. The cuticle of the posterior margin of the head serves as a spring, and is deformed by approximately 6% prior to a strike. The mandibles are likely unlatched by a subgroup of closer muscle fibers with particularly short sarcomeres. These fast fibers are controlled by two large motor neurons whose dendrites overlap with terminals of large sensory neurons originating from labral trigger hairs. Upon stimulation of the trigger hairs, the mandibles shut in as little as 0.5 ms and at peak velocities that are comparable with other trap-jaw ants, but with much slower acceleration. The estimated power output of the mandible strike (21 kW kg) confirms that jaws are indeed power amplified. However, the power output of mandibles is significantly lower than distantly related trap-jaw ants using different spring-loading mechanisms, indicating a relationship between power-amplification mechanism and performance.
诱捕颚蚁的特点是拥有用于捕食和防御的高速颚部。在蚂蚁中，动力放大颚部至少独立进化了四次，每个谱系使用不同的结构作为闩锁、弹簧和触发器。我们研究了蚁属（蚁亚科）的两个物种，它们的形态在诱捕颚蚁谱系中是独特的，并描述了其攻击的性能特征、弹簧加载机制和神经控制。与其他诱捕颚蚁一样，它们在大的闭合肌将势能加载到弹簧中时，会将颚部张开并保持张开状态。其闩锁与其他谱系不同，可能是由颚部张开肌和闭合肌的共同收缩形成的。头部后缘的角质层充当弹簧，在攻击前会变形约6%。颚部可能是由一组具有特别短肌节的闭合肌纤维解开闩锁的。这些快速纤维由两个大运动神经元控制，它们的树突与源自唇触须的大感觉神经元的终末重叠。当触须受到刺激时，颚部在短短0.5毫秒内关闭，峰值速度与其他诱捕颚蚁相当，但加速度要慢得多。估计的颚部攻击功率输出（21千瓦·千克）证实了其颚部确实是动力放大的。然而，该物种颚部的功率输出明显低于使用不同弹簧加载机制的远亲诱捕颚蚁，这表明动力放大机制与性能之间存在关联。
