File:Gigantometra gigas (Gerridae) DEAD LEG DOWNWARD MOVE.webm

English: This clip shows how midleg’s hairs capture air during fast downward movements in the water. The movements are slowed down (0.03125 normal speed). The movie (C0143) was captured in the field at 959.04 fps and saved in the format of 59.94 fps, which was additionally slowed down to 50%.

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