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

Abstract

The tail-flip escape behavior is a stereotypical motor pattern of decapod crustaceans in which swift adduction of the tail to the thorax causes the animal to rotate, move vertically into the water column and accelerate rapidly backwards. Previous predictions that a strong jet force is produced during the flip as the tail adducts to the body are not supported by our simultaneous measurements of force production (using a transducer) and the kinematics (using high-speed video) of tail-flipping by the California spiny lobster Panulirus interruptus. Maximum force production occurred when the tail was positioned approximately normal to the body. Resultant force values dropped 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, maximum acceleration of the body of free-swimming animals occurs when the tail is positioned approximately normal to the body, and acceleration declines steadily to negative values as the tail continues to close. Thus, the tail appears to act largely as a paddle. Full flexion of the tail to the body probably increases the gliding distance by reducing drag and possibly by enhancing fluid circulation around the body.Morphological measurements indicate that Panulirus interruptus grows isometrically. However, measurements of tail-flip force production for individuals with a body mass (M(b)) ranging from 69 to 412 g indicate that translational force scales as M(b)(0.83). This result suggests that force production scales at a rate greater than that predicted by the isometric scaling of muscle cross-sectional area (M(b)(2/3)), which supports previously published data showing that the maximum accelerations of the tail and body of free-swimming animals are size-independent. Torque (τ) scaled as M(b)(1.29), which is similar to the hypothesized scaling relationship of M(b)(4/3). Given that τ is proportional to M(b)(1.29), one would predict rotational acceleration of the body (α) to decrease with increasing size as M(b)(−)(0.37), which agrees with previously published kinematic data showing a decrease in α with increased M(b).