61.2 Sunday, Jan. 5 13:45 Motor control of an ultrafast spring-driven movement in smashing mantis shrimp KAGAYA, K.*; PATEK, S. N.; Dept. of Biology, Duke University, Durham, NC; Dept. of Biology, Duke University, Durham, NC firstname.lastname@example.org
Ultrafast movements are typically driven by springs that are loaded prior to movement. Given that muscles do not directly actuate the movement, how do spring-driven mechanisms generate variable kinematics? The extremely fast smashing behavior of mantis shrimp (Stomatopoda) was analyzed to understand the correlation between motoneuronal activity and strike kinematics. Mantis shrimp use extensor muscles to load the spring and flexor muscles to release it. Thus, we tested the hypothesis that the timing of flexor and extensor muscle contractions controls the kinematics of the mantis shrimp (Gonodactylus chiragra) raptorial strikes. We measured strikes using high speed imaging and simultaneously-recorded electromyograms of the extensor and flexor muscles. To load the spring, the lateral extensor units were activated followed by the lateral flexor units. Before the initiation of movement (16-59 msec), the extensor became non-active. We recorded the flexor activity for folding the appendages but could not record during extensor activation. Therefore, we used strike initiation in the video as the timing of flexor relaxation. Within individuals, the time difference between turning-off of the extensor and strike initiation had a negative linear relationship with maximum velocity. The results suggest that mantis shrimp can vary strike velocity through the timing of central nervous system signals. While variation in ultrafast movements likely occurs due to a constellation of factors, such as a nonlinear response of the mechanical system or environmental conditions, these results support a central nervous system-based control of ultrafast movement.