Capacity for sustained terrestrial locomotion in an insect: Energetics, thermal dependence, and kinematics

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Journal of Comparative Physiology B




The capacity for sustained, terrestrial locomotion in the cockroach. Blaberus discoidalis, was determined in relation to running speed, metabolic cost, aerobic capacity, and ambient temperature (T a=15, 23, and 34°C; acclimation temperature=24°C). Steady-state thoracic temperature (T tss) increased linearly with speed at each T a.The difference between T tss and T awas similar at each experimental temperature with a maximum increase of 7°C. Steady-state oxygen consumption (VO2ss) increased linearly with speed at each T aand had a low thermal dependence (Q10=1.0-1.4). The minimum cost of locomotion (the slope of the VO2ss versus speed function) was independent of T a.Cockroaches attained a maximal oxygen consumption (VO2max). increased with T afrom 2.1 ml O2·g-1·h-1 at 15°C to 4.9 ml O2·g-1·h-1 at 23°C, but showed no further increase at 34°C, VO2max increased 23-fold over resting VO2 at 23°C, 10-fold at 34°C, and 15-fold at 15°C. Endurance correlated with the speed at which VO2max was attained (MAS, maximal aerobic speed). Temperature affected the kinematics of locomotion. compared to cockroaches running at the same speed, but higher temperatures (23–34°C), low temperature (15°C) increased protraction time, reduced stride frequency, and reduced stability by increasing body pitching. The thermal independence of the minimum cost of locomotion (Cmin), the low thermal dependence of VO2ss (i.e., y-intercept of the VO2ss versus speed function), and a typical Q10 of 2.0 for VO2max combined to increase MAS and endurance in B. discoidalis when T awas increased from 15 to 23°C. Exerciserelated endothermy enabled running cockroaches to attain a greater VO2max, metabolic scope, and endurance capacity at 23°C than would be possible if T tss remained equal to T a. The MAS of B. discoidalis was similar to that of other arthropods that use trachea, but was 2-fold greater than ectotherms, such as salamanders, frogs, and crabs of a comparable body mass.