Experimental Studies and Dynamics Modeling Analysis of the Swimming and Diving of Whirligig Beetles (Coleoptera: Gyrinidae)

Whirligig beetles (Coleoptera, Gyrinidae) can fly through the air, swiftly swim on the surface of water, and quickly dive across the air-water interface. The propulsive efficiency of the species is believed to be one of the highest measured for a thrust generating apparatus within the animal kingdom. The goals of this research were to understand the distinctive biological mechanisms that allow the beetles to swim and dive, while searching for potential bio-inspired robotics applications. Through static and dynamic measurements obtained using a combination of microscopy and high-speed imaging, parameters associated with the morphology and beating kinematics of the whirligig beetle\u27s legs in swimming and diving were obtained. Using data obtained from these experiments, dynamics models of both swimming and diving were developed. Through analysis of simulations conducted using these models it was possible to determine several key principles associated with the swimming and diving processes. First, we determined that curved swimming trajectories were more energy efficient than linear trajectories, which explains why they are more often observed in nature. Second, we concluded that the hind legs were able to propel the beetle farther than the middle legs, and also that the hind legs were able to generate a larger angular velocity than the middle legs. However, analysis of circular swimming trajectories showed that the middle legs were important in maintaining stable trajectories, and thus were necessary for steering. Finally, we discovered that in order for the beetle to transition from swimming to diving, the legs must change the plane in which they beat, which provides the force required to alter the tilt angle of the body necessary to break the surface tension of water. We have further examined how the principles learned from this study may be applied to the design of bio-inspired swimming/diving robots. DOI: 10.1371/journal.pcbi.100279

Mini-/Micro-Scale Free Surface Propulsion

This work reports theoretical studies and experimental proofs of the propulsion of mini-/micro-scale floating objects that propel on air-liquid interface by using two different principles. The devices are extremely simple and do not include any moving parts. The first principle takes advantage of three-phase contact line oscillation that is activated by AC electrowetting on dielectric (EWOD) to propel the floating object. The capillary wave that is generated by the free surface oscillation is visualized by using the Free-Surface Synthetic Schlieren (FS-SS) method. A 3-D flow field sketch is constructed based on the flow visualizations and PIV measurements. The flow field and trajectories of seeded particles suggest that Stokes drift is the responsible mechanism for the propulsion. The propulsion speed of the floating object highly depends on the amplitude, frequency, and shape of the EWOD signal. These phenomena are also explained by the measured oscillation amplitudes and Stokes drift relations. Additionally, it is shown that a wider EWOD electrode generates a faster propelling speed. Finally, with stacked planar receiver coils and an amplitude modulated signal, a wirelessly powered AC EWOD propulsion is realized. The second principle of floating object propulsion is the Cheerios effect, which is also generally known as lateral capillary force. Four common physical configurations (interactions between two infinite vertical walls, two vertical circular cylinders, two spheres, and a sphere and a vertical wall) are reviewed. Through theoretical analysis, it has been revealed that not the wettability of the surface but the slope angle of the object is the most important parameter for the Cheerios effect. A general rule for this effect is that the lateral capillary force is attractive if the slope angles of the interacting objects have the same sign, otherwise the force is repulsive. In addition to the surface wettability, the size and the density of floating spheres are also important for the slope angle. Active control of the Cheerios effect is achieved by implementing EWOD and dielectrowetting methods to adjust the surface wettability. By sequentially activating micro-fabricated EWOD/dielectrowetting electrodes, linear translations of floating objects in the small scale channel are accomplished. A continuous rotational motion of the floating rod is achieved in a circular container by the EWOD method

소금쟁이과 거대 소금쟁이의 수면 위 거동에 대한 행동 및 형태학적 적응

학위논문(박사) -- 서울대학교대학원 : 자연과학대학 생명과학부, 2023. 8. Piotr G. Jablonski.Allometry is a study of the relationships between body size and other morphological and behavioral characteristics of an organism that result from the physics of the habitat and the biology of the organism living in its typical habitat. Water striders, Gerridae, is a good model taxon to study the locomotion and morphological adaptations to the laws of physics of their semiaquatic habitat: the water surface. The hydrodynamics and biomechanics of jumping and striding by water striders are well-understood in certain genera such as Gerris and Aquarius. Also, the hydrodynamic functions of micro hair structures on insect bodies have been studied in a relatively narrow range of water strider species. I studied two large-sized subtropical SE Asian species: Gigantometra gigas and Ptilomera tigrina. The body sizes of these species are approximately 2-10 times heavier than those of the typically studied species. The existing theory of jump of water striders predicts water striders use surface tension-dominant jump without surface breaking, which improves take-off velocity and reduces take-off delay. However, I observed that two large-sized species jump with surface-breaking and do not follow the existing theory of jump. I corrected the previous model without concerning drag to a model that includes drag calculation. The model shows that heavy species should break the water surface and utilize drag for thrust to achieve enough jump performance to escape from underwater predators. I developed another model that simulates floating conditions and sliding resistance of striding water striders. The model reveals that in order to float on the water surface, heavy species should have developed long forelegs to support the anterior part of the body with symmetric striding (two forelegs support the anterior body and two midlegs thrust simultaneously), or use asymmetric striding (one stretched forward midleg support the anterior body and another midleg and a contralateral hindleg thrust). The data on behavior observations and morphological measurements were consistent with the results of the model simulations. I explored the detailed micro-morphology of hair structures of the two species and observed how these structures are used by insects, by using scanning electron microscopy, optical microscopy, x-ray microscopy, and high-speed videography. The feasible match between the locomotive behavior of using legs and morphological characteristics of hairs implied hypothetical adaptive functions of these distinct hair structures of the two large species in comparison to the typical medium-sized water strider, A. paludum, that lives on stagnant water. Special hair brushes on the thrusting legs of P. tigrina were linked with their extremely fast striding behavior and fast-flowing habitat preference proven in this thesis. The theoretical modeling, observations, and experiments show how Gerridae illustrate adaptative links between the behavior, morphology, and habitat characteristics of organisms.Allometry는 서식지의 물리법칙과 유기체의 생물학적 특성으로 결정된 형태학 및 행동학적 특성이 몸 크기와 주고 받는 상호관계에 대한 연구이다. 소금쟁이과에 속하는 반수생 곤충들은 수표면이라는 특정한 환경에 살기 때문에 수면에서 활동하는 생명체의 운동을 관찰하고 수면의 물리법칙에 적응하여 습득한 형태학적 특징을 연구하기 위한 적합한 분류군이다. 소금쟁이의 수직도약과 수평이동에 대한 기존 연구들은 Gerris 및 Aquarius 와 같은 특정 분류군에 속하는 종을 대상으로 유체 역학 및 생체 역학적 원리에 초점을 맞춰왔다. 또한 몸체에 있는 미세모 구조의 유체 역학적 기능도 비교적 좁은 범위의 소금쟁이 종에서 연구되었다. 본 연구는 동남아에서 서식하는 Gigantometra gigas와 Ptilomera tigrina를 관찰, 실험 및 이론적 모델링을 진행함으로서 소금쟁이과(Gerridae)의 적응을 행동, 형태 및 서식지 특성으로 설명하고자 하였다. 이 종들의 몸무게는 기존 연구에서 널리 다뤘던 종들보다 2배에서 10배 가량 무겁기 때문에 지금껏 보고되었던 연구 모델의 가용성은 베일에 쌓여 있었다. 소금쟁이의 수직도약을 예측하는 기존 연구 모델은 수면의 표면 장력이 도약의 주요 추진력을 제공하기 때문에 소금쟁이가 수면을 깨지 않고 도약하여 도약 속도를 향상시키고 수표면 탈출 지연시간을 줄이는 것으로 예측했다. 하지만 본 연구에서 다루는 두 대형 종은 기존의 예측과 달리 수면을 깨뜨리면서 도약하기 때문에 기존 모델에 항력과 표면장력을 모두 포함하도록 수정하였다. 이를 토대로 두 종의 수직도약을 예측해본 결과, 표면장력 외에도 항력을 추진력으로 활용해야만 수중 포식자로부터 탈출하기에 충분한 도약 성능을 낼 수 있었다. 이밖에도 소금쟁이가 수면 위에 떠있기 위한 조건과 수면 위에서 미끄러질 때의 저항을 예측하는 모델도 개발하였다. 그 결과로 무거운 소금쟁이 종은 좌우 비대칭 추진(앞으로 뻗은 하나의 중간 다리가 앞쪽 몸체를 떠받치고 반대편 중간다리와 뒤쪽의 뒷다리로 추진하는 방식)을 하거나 좌우 대칭 추진(양쪽 앞다리가 앞쪽 몸체를 떠받치고 양쪽 중간다리로 동시에 추진하는 방식)을 하되 다른 종들보다 긴 앞다리로 앞쪽 몸체를 지지해야만 수면에 떠있을 수 있었다. 본 연구에서 시행된 행동 관찰과 형태학적 측정 데이터 또한 모델 예측 결과와 일치했다. 두 종의 자세한 마이크로 털 구조체와 그 사용방식은 주사전자현미경, 광학현미경, X선현미경, 고속영상촬영을 이용하여 관찰되었다. 흐르지 않는 물 위에 사는 일반적 크기의 소금쟁이 종인 A. paludum과 비교했을 때, 두 거대한 소금쟁이 종의 다리 사용 방식과 털의 형태학적 특성의 일치는 두 종의 독특한 털 구조체의 적응에 대한 가설을 시사한다. P. tigrina의 추진용 중간다리에 자라 있는 특수한 빗형 털 구조체는 이 연구에서 보여준 빠른 유속 서식지 선호도 및 고속 수평 이동과 관련이 있었으며 G. gigas의 중간다리의 긴 미세모와 뒷다리의 특수한 미세모로 이루어진 빔형태의 구조체 또한 좌우 비대칭 추진과 관련이 있는 것으로 보인다. 본 연구는 이론적 모델링과 관찰 및 실험을 사용해 소금쟁이과(Gerridae)의 행동 및 형태학적 적응을 서식지 특성에 연결하여 설명한다.Chapter 1. General Introduction 5 Chapter 2. Two different jumping mechanisms of water striders are determined by body size 12 Chapter 3. Physics of sliding on water predicts morphological and behavioral allometry across a wide range of body sizes in water striders (Gerridae) 72 Chapter 4. Functional micro-morphology of setae on legs of the heaviest semi-aquatic insect, the giant water strider (Gigantometra gigas) 119 Chapter 5. The micro-morphology of ribbon-like setae on midlegs of a large water strider from lotic habitats, Ptilomera tigrina, and their role in locomotion on the water surface 164 Chapter 6. Locomotion and flow speed preferences in natural habitats by large water striders, Ptilomera tigrina, with micro-morphological adaptations for rowing 187 Chapter 7. General discussion 210 References 221 Abstract in Korean 236박