Meeting Abstract
The mantle and funnel play familiar roles in providing power for and controlling the pulsed jet that squids use for swimming and maneuvering, but movements of the head toward and away from the mantle (i.e. acting like the plunger for the mantle “syringe”) may also be important modulators of the pulsed jet and the subsequent refilling of the mantle cavity. We investigated the morphology and the in vivo operating range and activation of the muscles that control head retraction and extension in Atlantic longfin squid (Doryteuthis pealeii). These muscles include the posterior (PNR) and anterior nuchal retractors (ANR), and the head retractor (HR) muscle. The ANR and HR are muscular hydrostatic organs composed of longitudinal, transverse, and circumferential muscle fibers, whereas the PNR is composed only of longitudinal fibers. Sonomicrometry records of 45 squid revealed that head retraction and extension precede mantle contraction and expansion significantly during jetting. The head experiences an impressive range of longitudinal strains during escape jets, with mean maximum extensions and retractions of +0.26 ± 0.29 and -0.64 ± 0.22, respectively. In addition, the muscles actuate the head at impressive strain rates, with mean maximum extension and retraction strain rates at 15°C of 1.61 ± 1.14 and -5.74 ± 3.8 muscle lengths s-1, respectively. Synchronized sonomicrometry and electromyography experiments in 17 squid revealed that longitudinal fibers are activated during head retraction in all three muscles, that transverse fibers in the HR and ANR are active during head extension, and that circumferential fibers in the HR are active both during extension and brief periods when head position is isometric. We also discovered two populations of longitudinal fibers in the HR and PNR that differ in the timing of their activation during head retraction. Funded by NSF grant IOS-0950827.
