Evidence of temperature‐independent metabolic rates in diurnal Namib Desert tenebrionid beetles

To investigate whether the sensitivity to environmental temperature varies between nocturnal and diurnal species of tenebrionid beetle, the metabolic rates of three diurnal species (Onymacris plana Peringuey, Onymacris rugatipennis Haag and Physadesmia globosa Haag) and three nocturnal species (Epiphysa arenicola Penrith, Gonopus sp. and Stips sp.) of beetles from the Namib Desert are measured over a range of temperatures (15–40 °C) that are experienced by these beetles in their natural habitat. The diurnal species O. plana, O. rugatipennis and P. globosa exhibit temperature‐independent metabolic rates (mean Q₁₀ = 1.2) within temperature ranges that are ecologically relevant for diurnal desert beetles (30–40 °C). Onymacris plana, in particular, has a 20–40 °C rate–temperature slope (0.007 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ = 1.1) that is less than half that of the other five beetle species (0.022–0.063 log₁₀ mL O₂ h^?1 g^?1 °C^?1; Q₁₀ ranges from 1.3–1.9), suggesting that O. plana is more metabolically independent of temperature than the other nocturnal and diurnal tenebrionids being investigated. Animals with metabolic rates that are decoupled from body temperature (or ambient temperature) may have an ecological advantage that allows them to exploit thermal and spatial niches during extreme temperature conditions.