The dynamics and scaling of force production during the tail-flip escape response of the California spiny lobster Panulirus interruptus

The tail-flip escape behavior is a stereotypical motor pattern of decapod c rustaceans in which swift adduction of the tail to the thorax causes the an imal to rotate, move vertically into the water column and accelerate rapidl y backwards. Previous predictions that a strong jet force is produced durin g the flip as the tail adducts to the body are not supported by our simulta neous measurements of force production (using a transducer) and the kinemat ics (using high-speed video) of tail-flipping by the California spiny lobst er Panulirus interruptus. Maximum force production occurred when the tail w as positioned approximately normal to the body. Resultant force values drop ped to approximately 15 % of maximum during the last third of the flip and continued to decline as the tail closed against the body, In addition, maxi mum acceleration of the body of free-swimming animals occurs when the tail is positioned approximately normal to the body, and acceleration declines s teadily to negative values as the tail continues to close. Thus, the tail a ppears to act largely as a paddle, Full flexion of the tail to the body pro bably increases the gliding distance by reducing drag and possibly by enhan cing fluid circulation around the body. Morphological measurements indicate that Panulirus interruptus grows isomet rically. However, measurements of tail-flip force production for individual s with a body mass (M-b) ranging from 69 to 412 g indicate that translation al force scales as M-b(0.83). This result suggests that force production sc ales at a rate greater than that predicted by the isometric scaling of musc le cross-sectional area (M-b(2/3)), which supports previously published dat a showing that the maximum accelerations of the tail and body of free-swimm ing animals are size-independent. Torque (tau) scaled as M-b(1.29), which i s similar to the hypothesized scaling relationship of M-b(4/3), Given that tau proportional toM(b)(1.29), one would predict rotational acceleration of the body (a) to decrease with increasing size as M-b(-0.37), which agrees with previously published kinematic data showing alpha decrease in a with i ncreased M-b.