EXOSKELETAL STRAIN - EVIDENCE FOR A TROT-GALLOP TRANSITION IN RAPIDLYRUNNING GHOST CRABS

Equivalent gaits may be present in pedestrians that differ greatly in leg number, leg design and skeletal type. Previous studies on ghost cr abs found that the transition from a slow to a fast run may resemble t he change from a trot to a gallop in quadrupedal mammals. One indicati on of the trot-gallop gait change in quadrupedal mammals is a distinct alteration in bone strain. To test the hypothesis that ghost crabs (O cypode quadrata) change from a trot to a gallop, we measured in vivo s trains of the meropodite of the second trailing leg with miniature str ain gauges. Exoskeletal strains changed significantly (increased fivef old) during treadmill locomotion at the proposed trot-gallop transitio n. Maximum strains attained during galloping and jumping (1000 X 10(-6 )-3000 x 10(-6)) were similar to the values reported for mammals. Comp arison of the maximum load possible on the leg segment (caused by musc ular tension) with the strength of the segment under axial loading rev ealed a safety factor of 2.7, which is similar to values measured for jumping and running mammals. Equivalent gaits may result from similari ties in the operation of pedestrian locomotory systems.