The Development of Spring-Actuated Mechanisms in Mantis Shrimp (Stomatopoda) and Snapping Shrimp (Alpheidae)

Latch-mediated spring actuation (LaMSA) mechanisms allow a broad diversity of organisms to achieve ultrafast motion. Most research into biological LaMSA mechanisms focuses on a narrow size or age range of the organism when the LaMSA mechanism is fully developed. However, the emergence of LaMSA morphology and behavior during early life history offers novel insights into the scaling and ecology of ultrafast movement. In this thesis, I establish the emergence and kinematics of LaMSA morphology in two systems, the mantis shrimp Gonodactylaceus falcatus (Stomatopoda) and the snapping shrimp Alpheus heterochaelis (Alpheidae). I also examine the plasticity of LaMSA development in the snapping shrimp Alpheus heterochaelis. The mantis shrimp’s spring-actuated strike is one of the best-studied LaMSA mechanisms; however, we do not know when the LaMSA morphology or behavior emerges during development. In Chapter 2, I found that the mantis shrimp G. falcatus develop their LaMSA morphology in their fourth larval stage when they transition into the pelagic zone and begin feeding on plankton. Mathematical and physical models of LaMSA kinematics suggest that smaller mechanisms generate greater accelerations. Therefore, I hypothesized that larval mantis shrimp would accelerate their strikes faster than adult mantis shrimp. Larval kinematics showed that larvae achieve accelerations on par or lower than adult mantis shrimp species. However, the larval strikes are much faster than the swimming speeds of other small pelagic organisms. Snapping shrimp generate cavitation bubbles using a LaMSA mechanism in their major claw. However, we do not know when the snapping shrimp LaMSA morphology or behavior emerges during development, nor whether they can generate cavitation bubbles at that size. In Chapter 3, I establish that the snapping shrimp Alpheus heterochaelis develop LaMSA morphology and behavior between one- and two months after hatching, when their carapace is roughly four to five millimeters long. I again hypothesized that the juvenile snapping shrimp would generate accelerations much faster than adults. My data show that juvenile snapping shrimp can generate accelerations two orders of magnitude faster than adults when the juvenile is more than two orders of magnitude smaller in claw mass. Juvenile snapping shrimp struck so quickly that they generated and directed cavitation bubbles at the millimeter scale. Developmental stressors can affect how morphological traits grow across ontogeny. In some cases, resource allocation to specific body parts during development can mitigate the negative effects of stress. To our knowledge, the developmental plasticity of LaMSA morphology and kinematics has not been explored. In Chapter 4, I test whether the development of the snapping shrimp LaMSA morphology and kinematics is affected by changes in feeding frequency. Juvenile snapping shrimp fed less frequently during development grew more slowly than better-fed individuals. However, the snapping shrimp raised in the least frequently fed group developed slightly larger snapping claws relative to their body size than individuals in other food treatments. Feeding treatments did not appear to affect the scaling of LaMSA kinematics. This thesis shows that the emergence of LaMSA morphology and behavior inform ecological transitions across ontogeny. The findings from this work can provide novel insights into how size may constrain ultrafast motion. The methods and systems I developed offer new systems and approaches for learning about the scaling and plasticity of spring-actuated movement.