Combining behavior and mechanics approaches reveals the dynamics of animal impacts in mantis shrimp (Stomatopoda)

Abstract

Animals deliver and withstand physical impacts in diverse behavioral contexts, from competing rams clashing their antlers together to archerfish impacting prey with jets of water. Though the ability of animals to withstand impact has generally been studied by focusing on morphology, behaviors may also influence impact resistance. Mantis shrimp exchange high-force strikes on each others coiled, armored telsons (tailplates) during contests over territory. Prior work has shown that telson morphology has high impact resistance. I hypothesized that the behavior of coiling the telson also contributes to impact energy dissipation. By measuring impact dynamics from high-speed videos of strikes exchanged during contests between freely-moving animals, I found that over 20% more impact energy was dissipated as compared to a prior study that focused solely on morphology. This increase is likely due to behavior: because the telson is lifted off the substrate, the entire body flexes after contact, dissipating more energy than exoskeletal morphology does on its own. While variation in the degree of telson coil did not affect energy dissipation, higher velocity strikes resulted in greater energy dissipation, suggesting striking individuals may vary their behavior to affect impacts. Overall, these findings show that analysis of both behavior and morphology is crucial to understanding impact resistance, and suggest future research on the evolution of structure and function under the selective pressure of biological impacts. Summary statementFreely competing mantis shrimp dissipated over 90% of the energy of high-force strikes by raising their impact-resistant tailplates off the substrate; faster strikes led to greater energy dissipation.