Abstract

Full, R.J. and Tullis, A. 1990. Capacity for sustained terrestrial locomotion in an insect: energetics, thermal dependence and kinematics. J. comp. Physiol. 160, 573-581.

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, was similar at each experimental temperature with a maximum increase of 7 C. Steady-state oxygen consumption, V(O2)ss increased linearly with speed at each T(a) and had a low thermal dependence (Q(10) = 1.0-1.4). The minimum cost of locomotion (the slope of the V(O2). versus speed function) was independent of T(a). Cockroaches attained a maximal oxygen consumption, V(O2)max. V(O2)max increased with T(a) from 2.1 ml O2/(g*h) at 15 C to 4.9 ml O2/(g*h) at 23 C, but showed no further increase at 34 C. V(O2)max, increased 23-fold over resting V(O2) at 23 C, 10-fold at 34 C, and 15-fold at 15 C. Endurancc correlated with the speed at which V(O2)max, 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, C(min), the low thermal dependence of V(O2)ss (i.e., y-intercept of the V(O2)max versus speed function), and a typical Q(10) of 2.0 for V(O2)max combined to increase MAS and endurance in B. discoidalis when T(a) was increased from 15 to 23 C. Exercise related endothermy enabled running cockroaches to attain a greater V(O2)max metabolic scope, and endurance capacity at 23 C than would be possible if T(1) 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.

Key words: Endurance - Locomotion - Energetics Temperature - Insects

Abbreviations: T(a) ambient temperature; T(1) thoracic temperature; T(tss)steady state thoracic temperature during exercise; T(trst) thoracic temperature during rest; V(O2) oxygen consumption; V(O2)rest oxygen consumption during rest; V(O2)ss steady-state oxygen consumption during exercise; V(O2)max maxirnal oxygen consumption; MAS maximum aerobic speed C(min) minimum cost of locomotion: t(end) endurance time