Meeting Abstract
During the aquatic nymphal stage, dragonflies possess a modified labium that functions as a high-speed raptorial appendage used in prey capture. During labial protraction, a preparatory phase of slow protraction is followed by the release of a latched knob-like structure in the elbow region of the labium, which results in a fast strike phase during which the appendage rapidly accelerates. The strike phase appears ballistic in nature, where relatively slow muscle contraction during the preparatory phase stores energy in associated elastic elements, and this energy is recovered via rapid recoil of the elastic structures once the latch disengages to produce a high-speed movement. We hypothesized that the performance (e.g., velocity, acceleration, work, power) of the non-ballistic preparatory phase should be thermally dependent, whereas the performance of the prospectively ballistic strike phase should have low thermal dependence. To test this hypothesis, individual nymphs were imaged (two cameras at 1000 Hz) capturing prey (California blackworm) at 15C, 25C, and 30C. We found that temperature affects the average and peak velocity of labial protraction during both the preparatory and strike phases. The effect on the preparatory phase was expected, given that the shortening velocity of ectotherm muscle is known to be temperature dependent. For the strike phase, high observed velocities indicate the presence of a ballistic component to the movement. However, because strike phase performance also is thermally dependent, it cannot be a purely ballistic movement like those observed in some invertebrate and vertebrate systems.
