Meeting Abstract
32.1 Friday, Jan. 4 Growing pains: the ontogeny of mantle muscle morphology, mechanics, and jetting in squids THOMPSON, J.T.*; BAKSI, A.E.; ROSS, K.E.; Franklin & Marshall College, Lancaster, PA; Franklin & Marshall College, Lancaster, PA; Franklin & Marshall College, Lancaster, PA joseph.thompson@fandm.edu
Squids (Cephalopoda, Mollusca) of all ages move using pulsed jets. The mantle and funnel of squids are essential in generating and modulating thrust for the pulsed jets. Previous research has demonstrated that aspects of the morphology, kinematics, and mechanics of the mantle and funnel differ dramatically between a newly hatched squid and juveniles or adults. We extended these studies by examining the morphology and mechanical properties of the mantle muscles that generate power for the jet in the long-finned squid, Doryteuthis pealei. The thick filament lengths of the central, mitochondria poor muscles of the mantle increased from 1.0 μm in hatchlings to 1.78 μm in adults. A decrease in maximum unloaded shortening velocity (VMAX) accompanied the increase in thick filament length, with VMAX declining from 9.2 L/s to 5.0 L/s at 20°C in hatchlings and adults, respectively. The higher VMAX of hatchlings may permit a higher rate of mantle contraction and may result in a more pulsatile jet. Work by others (e.g., D. Weihs, P. Krueger) suggests that a highly pulsed jet may increase propulsive efficiency. High-speed digital video studies of jetting by the squid in our study confirmed that the jets of hatchlings were more pulsatile than those of adults. The video analysis also showed that despite the significantly higher VMAX of the circular muscles of hatchlings, two aspects of escape jet performance, peak velocity and acceleration, were significantly lower in hatchlings. Thus, our findings, combined with work by others, may highlight a tradeoff during the evolution of jet locomotion in squids: selection for high propulsive efficiency in hatchlings but higher velocity and acceleration in juveniles and adults.
