Ritualized fighting and biological armor: the impact mechanics of the mantis shrimp's telson

Abstract

SUMMARY Resisting impact and avoiding injury are central to survival in situations ranging from the abiotic forces of crashing waves to biotic collisions with aggressive conspecifics. Although impacts and collisions in biology are ubiquitous, most studies focus on the material properties of biological structures under static loading. Here, we examine the mechanical impact properties of the mantis shrimp's telson, a piece of abdominal armor that withstands repeated, intense impacts from the potent hammer-like appendages used by conspecifics during ritualized fighting. We measured the coefficient of restitution, an index of elasticity, of the telson and compared it with that of an adjacent abdominal segment that is not impacted. We found that the telson behaves more like an inelastic punching bag than an elastic trampoline, dissipating 69% of the impact energy. Furthermore, although the abdominal segment provides no mechanical correlates with size, the telson's coefficient of restitution, displacement and impact duration all correlate with body size. The telson's mineralization patterns were determined through micro-CT (Computed Tomography) and correspond to the mechanical behavior of the telson during impact. The mineralized central region of the telson ‘punched’ inward during an impact whereas the surrounding areas provided elasticity owing to their reduced mineralization. Thus, the telson effectively dissipates impact energy while potentially providing the size-related information crucial to its role in conspecific assessment. This study reveals the mechanical infrastructure of impact resistance in biological armor and opens a new window to the biomechanical underpinnings of animal behavior and assessment.

From bouncy legs to poisoned arrows: elastic movements in invertebrates

“…They wield appendages that range from hammers that crush hard-shelled prey (Patek and Caldwell, 2005) to spear-shaped appendages that capture elusive prey (Caldwell and Dingle, 1976). Some species also use their raptorial appendages to settle disputes with conspecifics by hammering each other's telson (tail plate) (Caldwell, 1979), which functions like an inelastic punching bag to provide mechanical information about the size of each individual (Taylor and Patek, 2010).…”

A Sinusoidally Architected Helicoidal Biocomposite

“…[10][11][12][13][14] The dactyls of the "smashers", those that feed primarily on hard-shelled prey, (see Figure 1A) takes the form of a bulbous club ( Figure 1B), which is used to smash through mollusk shells, crab exoskeletons, and other tough mineralized structures with tremendous force and speed. [11][12][13][14][15][16] Achieving accelerations over 10,000g and reaching speeds of 23 m/s from rest, the dactyl strike is recognized as one of the fastest and most powerful impacting events observed in Nature. [11,12] The club is capable of delivering and subsequently enduring repetitive impact forces up to 1500 N and cavitation stresses without catastrophically failing, demonstrating its utility as an exceptionally damage-tolerant natural material.…”

Individual Recognition in Stomatopods

“…Both smashers and spearers use clicks. There is no evidence that clicks are used in individual recognition, but it is possible that clicks convey information about animal size in addition to serving as a general warning (Taylor and Patek 2010). Although not explicitly tested, it seems likely that molt stage might affect some of the properties of the strike signal as well.…”