Integrating the Physiology, Mechanics and Behavior of Rapid Running Ghost Crabs: Slow and Steady Doesn't Always Win the Race

Abstract

In 1979 Bliss predicted that, “land crabs are and will undoubtedly continue to be promising objects of scientific research.” Studies of rapid running ghost crabs support her contention and have resulted in several general findings relating to locomotion and activity. 1) Energy exchange mechanisms during walking are general and not restricted to quadrupedal and bipedal morphologies. 2) “Equivalent gaits,” such as trots and gallops, may exist in 4-, 6- and 8-legged animals that differ greatly in leg and skeletal ( i.e. , exo- vs . endoskeletal) design. These findings support the hypothesis that terrestrial locomotion in many species can modeled by an inverted pendulum or spring-mass system. 3) An open circulatory system and chitin-covered gills do not necessarily limit the rate at which oxygen consumption can be increased or the factorial increase oxygen consumption over resting rates. 4) Interspecific and intraspecific i.e. , ontogenetic) scaling of sub-maximal oxygen consumption and maximal aerobic speed can differ significantly. 5) Locomotion at speeds above the maximal aerobic speed requiring non-aerobic contributions may be far more costly than can be predicted from aerobic costs alone. The cost transport may attain a minimum at less than maximum speed. 6) The speed which elicits maximal oxygen consumption during continuous exercise is attained at moderate walking speeds in crabs and probably other ectotherms. Speeds 15- to 20-fold faster are possible, but cannot be sustained. 7) The low endurance associated with the low maximal oxygen consumption and maximal aerobic speed of ectotherms moving continuously can be increased or decreased by altering locomotor behavior and moving intermittently. Ectotherms can locomote at high speeds and travel for considerable distances or remain active for long periods by including rest pauses. Alternatively, intense activity with extended exercise periods with short pause periods may actually reduce behavioral capacity or work accomplished relative to continuous activity during which the behavior is carried out at a lower intensity level without pauses.