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.2006 Aug 22;103(34):12787-92.
doi: 10.1073/pnas.0604290103. Epub 2006 Aug 21.

Multifunctionality and mechanical origins: ballistic jaw propulsion in trap-jaw ants

Affiliations

Multifunctionality and mechanical origins: ballistic jaw propulsion in trap-jaw ants

S N Patek et al. Proc Natl Acad Sci U S A..

Abstract

Extreme animal movements are usually associated with a single, high-performance behavior. However, the remarkably rapid mandible strikes of the trap-jaw ant, Odontomachus bauri, can yield multiple functional outcomes. Here we investigate the biomechanics of mandible strikes in O. bauri and find that the extreme mandible movements serve two distinct functions: predation and propulsion. During predatory strikes, O. bauri mandibles close at speeds ranging from 35 to 64 m.s-1 within an average duration of 0.13 ms, far surpassing the speeds of other documented ballistic predatory appendages in the animal kingdom. The high speeds of the mandibles assist in capturing prey, while the extreme accelerations result in instantaneous mandible strike forces that can exceed 300 times the ant's body weight. Consequently, an O. bauri mandible strike directed against the substrate produces sufficient propulsive power to launch the ant into the air. Changing head orientation and strike surfaces allow O. bauri to use the trap-jaw mechanism to capture prey, eject intruders, or jump to safety. This use of a single, simple mechanical system to generate a suite of profoundly different behavioral functions offers insights into the morphological origins of novelties in feeding and locomotion.

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Conflict of interest statement

Conflict of interest statement: No conflicts declared.

Figures

Fig. 1.
Fig. 1.
Trap-jaw ants control the explosive release of stored energy through a combination of sensitive trigger hairs on the mandibles and an internal latch mechanism (9, 10). (a) A dorsal view of anO. bauri worker with mandibles cocked in preparation for a strike. (b) Left and right mandibles showing the dorsal surfaces (Upper) and leading edges (Lower). (Scale bar: 0.5 mm.)
Fig. 2.
Fig. 2.
The high-speed kinematics of trap-jaw strikes. (a) High-speed video images show a typical strike when an object is between the mandibles (20 μs between each frame). (b) The first mandible to move ina (open circles) strikes an object (filled squares, scaled to size) and pushes it toward the second mandible (filled circles). Zero represents the midline of the ant. (c) The second mandible to fire (a andb) (filled circles) attains a higher velocity than the first mandible (open circles). Movement opposite to the original direction of the strike is represented as negative velocity. (d) Corresponding to the images of an unobstructed strike (f), the first mandible to fire (open circles) scissors past the second (filled circles) as they cross the midline (at zero). (e) Corresponding tof, the second mandible to fire achieves a slightly higher velocity. (f) High-speed images show an unobstructed strike (20 μs between each frame). (Scale bars: 0.5 mm.) See Movie 1, which is published as supporting information on the PNAS web site.
Fig. 3.
Fig. 3.
Bouncer defense and escape jumps are characterized by distinct head orientations during mandible firing. (a) In a bouncer defense jump (see Movie 2), an ant approaches an “intruder” (plastic strip outlined in gray at 0.00 ms) with its jaws cocked and open. The jaws are then closed against the intruder (0.67 ms), propelling the ant’s head and body upward (1.33 and 5.00 ms, respectively). (b) In an escape jump (see Movie 3), an ant aligns its cocked jaws perpendicularly to the substrate (0.00 ms). When it strikes (0.33 ms), the head and body are propelled upward (0.66 and 4.33 ms, respectively). (Scale bars: 1 cm.)
Fig. 4.
Fig. 4.
The predicted and observed trajectories of bouncer defense and escape jumps. Dashed lines represent actual digitized trajectories of four typical jumps. Solid lines depict “drag-free” trajectories based on the initial conditions of the jumps. Escape jumps (gray and black lines) yielded greater heights and, on average, double the airborne duration observed in bouncer defense jumps (blue and green lines). On average, the ranges of bouncer defense jumps were seven times greater than escape jumps. Digitized data were sampled at intervals of 17 ms from the high-speed video sequences, which were filmed at 3,000 frames per second (see Movies 3–5).
Fig. 5.
Fig. 5.
A high-speed image sequence of an escape jump using jaw propulsion in response to the presence of a larger heterospecific competitor (O. erythrocephalis) in the filming arena. Shown starting in the top-right image, the ant indicated by an arrow directs and fires its cocked mandibles against the substrate. The ant is propelled upward through the air toward the left of the page. The ant descends to the left of the page in the second half of the trajectory. Images are shown at 13.3-ms intervals (see Movies 3 and 5). (Scale bar: 1 cm.)
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