Data from: Strike mechanics of an ambush predator: the spearing mantis shrimp

Ambush predation is characterized by an animal scanning the environment from a concealed position and then rapidly executing a surprise attack. Mantis shrimp (Stomatopoda) consist of both ambush predators (ʻspearersʼ) and foragers (ʻsmashersʼ). Spearers hide in sandy burrows and capture evasive prey, whereas smashers search for prey away from their burrows and typically hammer hard-shelled, sedentary prey. Here, we examined the kinematics, morphology and field behavior of spearing mantis shrimp and compared them with previously studied smashers. Using two species with dramatically different adult sizes, we found that strikes produced by the diminutive species, Alachosquilla vicina, were faster (mean peak speed 5.72±0.91 m s^−1; mean duration 3.26±0.41 ms) than the strikes produced by the large species, Lysiosquillina maculata (mean peak speed 2.30±0.85 m s^−1; mean duration 24.98±9.68 ms). Micro-computed tomography and dissections showed that both species have the spring and latch structures that are used in other species for producing a spring-loaded strike; however, kinematic analyses indicated that only A. vicina consistently engages the elastic mechanism. In the field, L. maculata ambushed evasive prey primarily at night while hidden in burrows, striking with both long and short durations compared with laboratory videos. We expected ambush predators to strike with very high speeds, yet instead we found that these spearing mantis shrimp struck more slowly and with longer durations than smashers. Nonetheless, the strikes of spearers occurred at similar speeds and durations to those of other aquatic predators of evasive prey. Although counterintuitive, these findings suggest that ambush predators do not actually need to produce extremely high speeds, and that the very fastest predators are using speed to achieve other mechanical feats, such as producing large impact forces.伏击捕食（ambush predation）的核心特征为动物从隐蔽位置探查环境，随后快速发起突袭。螳螂虾（Stomatopoda，mantis shrimp）包含两类生态类群：伏击捕食者（即‘矛击型’个体）与觅食者（即‘粉碎型’个体）。矛击型个体隐匿于沙质洞穴内，捕食机动性较强的猎物；而粉碎型个体则脱离洞穴搜寻猎物，通常以具坚硬外壳的固着性猎物为食。本研究针对矛击型螳螂虾的运动学、形态学与野外行为展开系统研究，并与此前已被深入探究的粉碎型螳螂虾进行对比分析。我们选取成体体型差异悬殊的两个物种开展实验，结果显示体型更小的阿拉科斯虾蛄（Alachosquilla vicina）的攻击峰值速度更快（平均峰值速度为5.72±0.91 m·s⁻¹；平均攻击时长为3.26±0.41 ms），显著高于体型较大的斑条虾蛄（Lysiosquillina maculata）（平均峰值速度为2.30±0.85 m·s⁻¹；平均攻击时长为24.98±9.68 ms）。微计算机断层扫描（micro-computed tomography）与解剖实验结果表明，两个物种均拥有与其他物种同源的弹簧-闩锁结构，该结构是部分物种实现蓄力式攻击的核心结构；但运动学分析显示，仅阿拉科斯虾蛄会稳定启用该弹性蓄力机制。野外观测发现，斑条虾蛄主要在夜间隐匿于洞穴中伏击机动性猎物，其攻击时长相较于实验室拍摄的视频呈现出长短两种模式。我们最初曾推测伏击捕食者的攻击速度应达到极高水平，但研究结果却与之相反：矛击型螳螂虾的攻击速度反而慢于粉碎型螳螂虾，且攻击时长更长。不过，矛击型螳螂虾的攻击速度与时长，与其他以机动性猎物为食的水生捕食者的表现相近。尽管这一发现与直觉相悖，但本研究结果表明，伏击捕食者实际上并不需要极致的高速度；而那些速度最快的捕食者，实则是借助速度来达成其他力学功效，例如产生巨大的冲击力。