Ventilation in Namib Desert Tenebrionid Beetles: Mass Scaling and Evidence of a Novel Quantized Flutter-Phase

The mass scaling of discontinuous ventilation (DV) phenomena in adult motionless insects is currently unknown. I present DV phenomena from 10 species of Namib Desert tenebrionid beetles; four from the dune-sea habitat, five from the river-bed habitat and one from the gravel plain habitat, which is characterized by very low and patchy resource availability. This species differed from the others in many respects. However, all species exhibited a previously undescribed, convective and quantized F phase ventilation (ISP, or intermittent serial pulsation, phase). For dune-sea and river-bed habitat species, all DV characteristics except DV frequency (V phase CO₂ emission volume and rate, total and per-burst ISP phase CO₂ emission volume, and total rate) scaled tightly with body mass with a scaling exponent close to 1.0 (typical r²>0.95-0.98), as did overall rate of CO₂ production and hence metabolic rate (MR). Consequently these parameters were independent of body mass when expressed on a mass-specific basis, explaining the independence of body mass and DV frequency. These findings are compatible with published DV data in other species and orders of insects, suggesting that these scaling phenomena may be widespread. The gravel plain species (Epiphysa arenicola) had an MR of 38%, V phase CO₂ volume of 41% and V phase CO₂ emission rate of 23% of those predicted on the basis of its body mass, and it emitted a greater proportion of CO₂ during its ISP phase (47% vs 24% of total CO₂ output per DV cycle in the other species). It is suggested that these discrepancies are respiratory and ventilatory adaptations to scarce and patchy energy and water availability.