File:Gigantometra gigas (Gerridae) JUMP IN THE TANK 4.webm

English: This clip shows a close-up on legs seen approximately from the side to illustrate that during fast leg downward movements the air sheath (air bubble) around the legs is extended along the direction of leg movements (also seen in the two other clips: JUMP IN THE TANK 2 and DEAD LEG DOWNWARD MOVE. Therefore we could imagine that a crossection of leg including the air bubble may resemble an irregular ellipse rather than a circle. The drag force is proportional to the effective leg diameter, which is a function of the diameter of the leg plus the thickness of the air measured during downward movement in the plane perpendicular to the leg downward movement (see Supplementary Materials PART 7 for more details on how this aspect was simplified in the theoretical model). The movements are slowed down (0.015625 normal speed). The movie (C0046) was captured with Sony RX10-III at 959.04 fps and saved in the format of 59.94 fps, which was additionally slowed down to 25%.

SUPPLEMENTARY VIDEO TO: Allometry of jumping on water by water striders by Woojoo Kim1&, Juliette Amauger2&, Jungmoon Ha1, Thai Pham Hong3,4, Duc Anh Tran5, Jae Hong Lee6, Jinseok Park1, Piotr G. Jablonski1,7*, Ho-Young Kim 6*, Sang-im Lee8*

EXTRA SUPPLEMENTARY VIDEOS

Affiliations: 1 Laboratory of Behavioral Ecology and Evolution, School of Biological Sciences, Seoul National University, Seoul 08826, Korea 2 LadHyX, UMR 7646 du CNRS, École polytechnique, 91128 Palaiseau, France 3 Mientrung Institute for Scientific Research (MISR), Vietnam Academy of Science and Technology (VAST), 321 Huynh Thuc Khang St, Hue, Vietnam 4 Graduate University of Science and Technology, VAST, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam 5 Department of Applied Zoology, Faculty of Biology, University of Science, Vietnam National University, Hanoi, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam 6 Department of Mechanical Engineering, Seoul National University, Seoul 08826, Korea 7 Museum and Institute of Zoology, Polish Academy of Sciences, Wilcza 64, 00-679 Warsaw, Poland 8 Laboratory of Integrative Animal Ecology, Department of New Biology, DGIST, Korea

Abstract Current theory for surface-tension dominated jumps, created for small and medium size water strider species and used in bio-inspired engineering, predicts that jumping individuals are able to match their downward leg movement speed to their size and morphology such that they maximize the takeoff speed and minimize the latency to takeoff without breaking the surface. Here, we use empirical observations and theoretical hydrodynamic modeling to show that large species do not conform to this theory and switch (“switching” body size range: ~50 to ~80 mg) to using the surface-breaking rather than surface-tension-based jumps in order to achieve jumping performance sufficient for protecting them from attacking underwater predators. This illustrates that natural selection for a performance that minimizes mortality may break the theoretical scaling relationship predicted from a specific biomechanics leading to a switch/shift to a new biomechanical mechanism that results in an outcome favored by natural selection.

Keywords: water strider, surface tension, jumps, antipredatory, water surface, Gerridae, drag, biomechanics, hydrodynamics, allometry