Using high-speed video recordings, we carried out an analysis of the locomotion gaits of the following aquatic Heteroptera: coral treaders Hermatobates weddi (Hermatobatidae), sea striders Halovelia septentrionalis (Veliidae), and water striders Metrocoris histrio (Gerridae), in the Island of Amami Oshima, Kagoshima Prefecture, Japan. Most insects use an alternating double tripod gait for walking, whereas species of Gerridae and some Veliidae use a synchronous rowing gait. We found that H. weddi used a peculiar locomotion gait, a modification of the double tripod gait. In this special gait, two alternating dipods (mid and hind legs) are used, while the forelegs remained inactive. Contralateral mid and hind stroked simultaneously. The mid leg recovered immediately after the stroke; however, the hind leg was delayed and remained extended after the stroke. Next, the following bipod stroked, and when that mid leg finished the stroke, both ipsilateral mid and hind (the one which did not recover after the stroke) legs recovered together. Turning is also unique in H. weddi because the body axis rotation and the course turning (deflection) were clearly separated in two phases. We compared the kinematics of H. weddi pattern with the synchronous rowing pattern found in H. septentrionalis and M. histrio and discussed some biomechanical consequences. We also analyzed phylogenetic implications of this gait, and we posit that the modified double dipod gait is a uniquely derived character of the family Hermatobatidae. The synchronous rowing gait would be an autapomorphy for the clade Gerridae ? Veliidae. The modified thorax, with the meso and metacoxae horizontally directed, would be a synapomorphy for the superfamily Gerroidea (Hermatobatidae, Gerridae, and Veliidae).
Phoretic motion of particles along a temperature gradient formed in a fluid, known as thermophoresis, often takes place under the influence of bulk motion caused by thermal convection. In this paper, using a laser heating method, the significance of two competing effects, that is, thermophoresis and thermal convection, for the particle transport in a liquid phase confined in a microgap is investigated experimentally by changing the gap size as a control parameter. It is found that there is a threshold of the gap size, above which the particles tend to accumulate around the heated spot, forming a ring‐like particle distribution. On the contrary, if the gap size is below the threshold, the particles are depleted from the heated spot. Switching between these accumulation and depletion modes is expected to develop novel manipulation techniques.
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