Abstract

Weinstein, R., and Full, R.J. 1994. Thermal dependence of locomotor energetics of the ghost crab, Ocypode quadrata. Physiol. Zool. 67, 855-872.

We tested a general modelpredicting the effect of body temperature (T(b)) on the aerobic capacity, metabolic cost, and endurance of sustained, terrestrial locomotion. In the ghost crab, Ocypode quadrata, T(b) was a function of ambient temperature (T(a)), relative humidity (RH), and the duration of acute exposure. At 15° C and 24° C, T(b) was similar to T(a). At high T(a) (30° C to 350 C) and low RH (4096 to 5096), T(b)'s were 6° C below T(a). When the RH was 9996-10096 at a Ta of 300 C, T(b) stabilized at 29. 7° C. The depression in T(b) resulted from evaporative water loss. The maximal rate of oxygen consumption (V(O2)max), determined during treadmill exercise, decreased by nearly 7596 as T(b) was decreased from 24°C to 150 C. The minimum cost of locomotion (C(min), the slope of the steady state oxygen consumption vs. speed function) did not change at low T(b) (150 C). As T(b) was increased from 24°C to 30°C, V(O2)max decreased to half of its original value. At the lowest walking speeds, steady state oxygen consumption (V(O2)ss) at a T(b) of 30° C did not differ significantly from or may have even exceeded that at a T(b) of 24° C (the yintercept of the V(O2)ss vs. speed function was elevated relative to resting rates). The minimum cost of locomotion decreased by nearly two-thirds when T(b) was raised from 24° C to 30° C. The reduced C(min) increased the range of sustainable speeds by nearly threefold over thatpredicted from a thermally insensitive C(min) at a T(b) of 30°C. Endurance correlated with the speed at which V(O2)max was attained (maximum aerobic speed) and, therefore, was reduced significantly at both low and high temperatures. On the basis of the present study of quantified locomotion, we conclude that thermal optima of maximal oxygen consumption and endurance are caused by a true thermal effect on oxygen utilization and muscle function rather than by a submaximal effort by the animal.