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First published online February 6, 2004
Journal of Experimental Biology 207, 913-922 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00843

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Kinematics and hydrodynamics of swimming in the mayfly larva

John Brackenbury

Department of Anatomy, University of Cambridge, Downing Street, Cambridge CB2 3DY, UK

View larger version (40K): [in a new window]   Fig. 1. Experimental technique for drag measurement in dead specimens. (A) Side view and (below) plan view of water-bath mounted on turntable and containing insect holder attached to force transducer. For ease of presentation, the insect holder has been enlarged: the length of the horizontal `hook' was 3.5 mm, and the diameter of the vessel was 12 cm. Arrows in plan view indicate water flow. (B) Enlarged view of insect holder. (C) Experimental findings; see text for further details. (D) Original recordings of drag measurement. The first arrow on the left indicates the point at which the turntable was activated at the slower speed. Within approximately 1 min, a stable flow regime was established. At the point shown by the second arrow, the turntable was switched to the higher speed. The third arrow marks the point at which the turntable was switched off and flow steadily declined to zero. After a delay of 1 min, the series was repeated to give a duplicate set of recordings for this individual.

View larger version (28K): [in a new window]   Fig. 8. Kinematics of rapid-start (A,D) and turn-about (B,C) manoeuvres. Resting positions of the larvae are indicated by 0 ms, and the insects are viewed from the side and facing to the right of the page. The dorsal surface of the body is stippled for ease of identification during the following manoeuvres. In each case, the larva receives a light touch to the right side of its head. Details are given in the text. C shows a turn-about manoeuvre in fixed co-ordinates (left). Filled and open circles represent the motion of the fin tip and head, respectively, at 20 ms intervals. The two drawings below and on the right, respectively, show the start and finish positions of the body during a turn-about. Dashed outlines plot the motion of ring vortices released during the extension phase of the manoeuvre and during the final upward tail-flick, respectively. Arrows show the direction of propagation of the ring vortices. (D) Dorsal view of a larva performing a rapid start; , turning angle.

View larger version (101K): [in a new window]   Fig. 2. Trail produced by the wake of a continuously swimming mayfly larva. The larva is swimming on its side just above the bottom layer of milk and is viewed from above. It is pursuing a slightly curved path from top left to bottom right. (a) The initial trace consists of a sinuous line coinciding with the motion of the tail fin. (b) The appearance of a fully formed trail 0.5 s after the events shown in a. Profiles of the larva are shown at successive 40 ms intervals. The mature trail consists of a ladder-like series of areas, each corresponding to a half-stroke, in which the general motion (as indicted by the arrows) of the dye is nearly at right angles to the swimming line.

View larger version (118K): [in a new window]   Fig. 3. Trail produced by the wake of a continuously swimming mayfly larva. The larva is swimming upright just above the bottom layer of milk and is viewed from above. (a) The larva is swimming in the direction indicated by the arrow: the larva is seen in dorsal view and the three tail fin bristles can be identified. At this point, there is no indication of the wake. (b) 0.4 s later, the larva has progressed beyond the field of view, and three roughly circular impressions have appeared in the bottom layer. As explained in the text, these were produced by three consecutive half-strokes executed to the ventral side of the swimming line.

View larger version (63K): [in a new window]   Fig. 4. Progressive visualisation of a discrete ring vortex shed from the tail fin of a swimming mayfly larva. In a, the larva is swimming in the direction of the arrow and is viewed from the side (dorsal to the left). The tail fin is within 20 ms of the completion of its dorsal half-stroke. To the left of the larva is a curved streamer. Subsequent frames (b,c) show the progressive outlining of the ring vortex shed from the tail as it penetrates the streamer. See text for more details. The arrow in b shows the direction of propagation of the ring vortex.

View larger version (134K): [in a new window]   Fig. 5. A ring vortex approximately 0.5 s after penetrating a dye streamer. The arrow shows the direction of propagation of the ring vortex. Note the ellipsoidal shape of the vortex, the outlining of the vortex core and the continuing movement of dye into the trailing edge of the vortex.

View larger version (96K): [in a new window]   Fig. 6. Visualisation of a train of consecutive ring vortices shed to the dorsal side of the swimming line. The larva is swimming obliquely upwards, as indicated by the broken arrow in a, and is viewed from its right side (dorsal side is to the left of the profile). On the far left in a is a vertical dye streamer. b and c show stages in the penetration of the streamer by ring vortices released from the larva during consecutive dorsal half-strokes. The arrows in b and c indicate the direction of propagation of the ring vortices.

View larger version (18K): [in a new window]   Fig. 7. (A) Flow variables measured during mayfly larval swimming. A scheme of an individual ring vortex is shown on the left and of the pattern of ring vortex shedding on the right. Abbreviations: r, ring radius; rp, ring vortex radius measured at the ring plane; ra, ring vortex radius measured along the vortex axis; jet, jet velocity relative to the surrounding water measured at the ring plane; U, forward velocity; , momentum axis of the ring vortex in the median plane of the body. (B) Velocity profiles measured along the vortex axis in three separate ring vortices. The data represent the distance travelled by the dye front, during consecutive 20 ms intervals, as it progressed from the trailing edge to the leading edge of the ring vortex. The data are given in vortex fixed coordinates and therefore represent the re-circulatory component of the axial jet.