Energetics of locomotion and patterns of respiration in tenebrionid beetles from the Namib Desert

Abstract

1. Rates of oxygen consumption\(\left( {\dot V_{O_2 } } \right)\) were measured in 4 species of flightless tenebrionids ranging in mass from 0.6 to 1.3 g. Three were fast-moving day-active species (Onymacris plana, Physadesmia globosa, Physosterna cribripes), and one was slow-moving and crepuscular (Epiphysa arenicola). 2. For motionless animals at 22–24 °C during the inactive phase of their daily cycle, the regression of log\(\dot V_{O_2 } \) (ml O2/h) on mass (g) is described by Y=0.105X0.796. 3. In maleO. plana\(\dot V_{O_2 } \) increased with running speed up to 13 cm/s. From 13 to 22 cm/s the slope of the regression of\(\dot V_{O_2 } \) on speed did not differ significantly from zero. We hypothesize that the independence of\(\dot V_{O_2 } \) and high running speeds inO. plana results from the generation of aerodynamic lift by its flattened and laterally expanded body which acts as an airfoil. InP. globosa andP. cribripes\(\dot V_{O_2 } \) increased linearly with running speed at all speeds measured. 4. \(\dot V_{O_2 } \) was strongly cyclical. The periodicity was most conspicuous in motionless animals but was also apparent during locomotion. The cycles corresponded with periods of ventilation associated with episodes of pumping by the abdomen which lies within a space inclosed in a rigid chitinous capsule formed by the fused elytra and fused abdominal sternites. 5. Factorial metabolic scope was greates inO. plana, the most cursorial of the species studied.