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Synopsis The air–water interface of the planet’s water bodies, such as ponds, lakes, and streams, presents an uncertain ecological niche with predatory threats from above and below. As Microvelia americana move across the water surface in small ponds, they face potential injury from attacks by birds, fish, and underwater invertebrates. Thus, our study investigates the effects of losing individual or pairs of tarsi on M. americana’s ability to walk on water. Removal of both hind tarsi causes M. americana to rock their bodies (yaw) while running across the water surface at $$\pm 19^{\circ }$$, compared to $$\pm 7^{\circ }$$ in nonablated specimens. This increase in yaw, resulting from the removal of hind tarsi, indicates that M. americana use their hind legs as “rudders” to regulate yaw, originating from the contralateral middle legs’ strokes on the water’s surface through an alternating tripod gait. Ablation of the ipsilateral middle and hind tarsi disrupts directionality, making M. americana turn in the direction of their intact limbs. This loss of directionality does not occur with the removal of contralateral middle and hind tarsi. However, M. americana lose their ability to use the alternating tripod gait to walk on water on the day of contralateral ablation. Remarkably, by the next day, M. americana adapt and regain the ability to walk on water using the alternating tripod gait. Our findings elucidate the specialized leg dynamics within the alternating tripod gait of M. americana, and their adaptability to tarsal loss. This research could guide the development and design strategies of small, adaptive, and resilient micro-robots that can adapt to controller malfunction or actuator damage for walking on water and terrestrial surfaces.
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Epineuston vortex recapture enhances thrust in tiny water skaters
Vortex recapture underpins the exceptional mobility of nature’s finest fliers and swimmers. Utilized by agile fruit flies and efficient jellyfish, this phenomenon is well-documented in bulk fluids. Despite extensive studies on the neuston—a vital fluidic interface where diverse life forms interact between air and water—neuston vortical hydrodynamics remain unexplored. We investigate epineuston (on water) vortical hydrodynamics inMicrovelia americana, one of the smallest and fastest water striders, skating at 50 BL/s (15 cm/s). Their middle legs shed counter-rotating vortices, re-energized by hind legs, demonstrating epineuston vortex recapture. High-speed imaging, particle imaging velocimetry, physical models, and CFD simulations show re-energization increases thrust by creating positive pressure at the hind tarsi, acting as a virtual wall. This vortex capture is facilitated by the tripod gait, leg morphology, and precise spatio-temporal placement of the hind tarsi during the power stroke. Our study extends vortex recapture principles from bulk fluids to the neuston, offering insights into efficient epineuston locomotion, where surface tension and capillary waves challenge movement. Understanding epineuston vortex hydrodynamics can guide the development of energy-efficient microrobots to explore the planet’s neuston niches, critical frontlines of climate change and pollution.
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- PAR ID:
- 10537386
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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Mate choice and male–male combat over successful mating often cause disproportionate exaggeration of male trait relative to body size. However, the exaggeration is often not the only trait involved with male–male combat and mate choice: suites of co-expressed traits may function together as a coordinated unit. When this occurs, dimorphism may be expected for these additional, non-exaggerated, structures. S. femorata males have disproportionately large hind-legs used in male–male combat over females. During the fights, fore- and mid-legs are used to keep males in positions where advantageous for leverage. Because use of the exaggerated hind-legs is coordinated with the other legs, they will coevolve as a functional unit. Here, we show that 1) S. femorata has sexual size differences in all three legs; 2) males show positive allometry in the relative sizes of all three legs; and 3) microstructures of tarsi on the fore- and mid-legs are also sexually dimorphic. Despite these differences in the tarsal microstructure, 4) adhesion forces of the tarsi had no sexual difference in flat surface. The microstructure would be specialized on attaching elytra surface. These results suggest that the three pairs of legs function together during fighting behavior, with hind-legs employed primarily for fighting, and the fore- and mid-legs functioning to grip females, keeping males positioned on the back of the female during combat.more » « less
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.1101/2024.06.17.599397
