Latch-Mediated Spring Actuation and the Diversity of Ultrafast Trap-Jaw Ant Impacts, Witch Hazel Fruit Sizes, and Spring-Launched Seed Aerodynamics
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2024
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Recently, a framework of latch-mediated spring actuation (LaMSA) outlined the general mechanism shared by organisms across the tree of life that use springs and latches to generate motion. Specifically, the framework describes how motion is possible through the integration of a motor, spring, latch, and projectile. First, a motor stores elastic potential energy into a spring by deforming it. A latch then mediates the transformation of elastic potential energy in the spring into kinetic energy of the projectile. Comparative analyses within and across diverse organisms that use LaMSA have revealed the remarkable integration between components. For example, differences in how the spring is tuned to the motor can explain variations in the amount of energy stored in a spring. While the characteristics of the spring, such as its stiffness, define the limits of energy storage, the amount of energy that is stored in the spring also depends on how far it is deformed by the motor. Therefore, the characteristics of biological motors, such as the pennation angle of muscle fibers or the permeability of tissues to generate internal turgor pressures, also affect energy storage. Likewise, integration of the latch and projectile cause variations in the amount of energy released by a LaMSA system. Differences in the shape and speed of the latch as well as the mass and shape of the projectile can lead to differences in energy release. I investigate the integration between the spring and projectile in LaMSA systems by comparing how springs change as projectiles increase in mass. Additionally, I examine how the projectile is integrated with its environment. Variations in the materials or masses of the targets impacted by LaMSA systems may lead to differences in interactions, quantified through energy exchange. Likewise, variations in the projectile may affect interactions with the environment. Specifically, projectiles launched by LaMSA systems may have varying aerodynamics depending on the size of the projectile and its motion through the air. I address scaling across springs and projectiles through investigations of three seed-launching species in the witch hazel family (Hamamelidaceae). I examine the integration between the projectile and the environment through investigations of the mandible strikes of a trap-jaw ant (Odontomachus brunneus) and comparing the trajectories of seeds launched by Hamamelis virginiana. In chapter 2, I measured the transfer of energy from the mandibles of a trap-jaw ant, Odontomachus brunneus, into targets of various masses and materials. Using a device that I created and validated, I demonstrated that when the roughly 50 µg mandibles of O. brunneus moving at accelerations of 105 m s-2 impacted a target made of a compliant material, the energy losses were lower than expected from traditional drop tests on the same material (using much larger masses and lower accelerations). Additionally, I found that strikes against targets that weighed 0.4 grams had similar amounts of energy transfer as targets that were fixed in place suggesting that strikes against masses above 0.4 grams would be inertially similar. In chapter 3, I compared the amount of elastic potential energy stored in the springs of three seed-launching species in the witch hazel family (Hamamelidaceae). These three species share a similar seed launching mechanism. I revealed that across an order of magnitude in seed masses, launch speeds remained constant due to differences in the capacity of the springs to store elastic potential energy. As seed mass increased, spring mass increased along with the spring’s capacity to store elastic potential energy. Finally, as fruits increased in size, less elastic potential energy was converted to kinetic energy of the seed, suggesting a trend of increased energetic losses as spring-launch systems increase in size. In chapter 4, I discovered that the range of H. virginiana seeds was affected by launch angle, seed kinetic energy, drag, and lift. Individually, launch angle, seed kinetic energy, drag and lift did not explain the variance in the seed’s range. Instead, combinations of these parameters, specifically, the combination of launch angle and kinetic energy and the combination of drag and lift, better explained variations in range. Between these combinations of parameters, the ballistic range of seeds was most sensitive to changes in drag and lift. Additionally, I found that the periodic oscillations in the orientation of the seed throughout its trajectory were associated with the magnitude of drag and the magnitude and direction of lift. Overall, this dissertation presents new insights about the impact dynamics of small, high acceleration impacts, the scaling of springs and projectiles, and unexpected aerodynamics of spinning projectiles. LaMSA systems that impact targets may vary in energy release depending on the material and mass of the target. Additionally, differences in the mass of the projectile may lead to changes in the energy storage capacity of springs. Finally, the range that LaMSA systems can launch their seeds may depend on how the seed is launched as well as the interactions between the seed and air. Through this dissertation, I present how, through large datasets and comprehensive analyses, we can understand the integration between the spring, projectile, and environment.
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Jorge, Justin Frederic (2024). Latch-Mediated Spring Actuation and the Diversity of Ultrafast Trap-Jaw Ant Impacts, Witch Hazel Fruit Sizes, and Spring-Launched Seed Aerodynamics. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/30947.
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