Metabolic rate and respiratory gas-exchange patterns in tenebrionid beetles from the Negev Highlands, Israel

This study correlates the pattern of external gas exchange with the diel activity of nine species of tenebrionid beetle from the Negev Desert, Israel. The study species are active throughout the summer months when daytime temperatures are high and no rain falls. There were no differences in standard metabolic rate, determined by flow-through respirometry, among the nine species. All the nocturnally active beetles exhibited a form of continuous respiration, whereas the two diurnally active and one crepuscular species exhibited a cyclic form of respiration referred to as the discontinuous gas-exchange cycle (DGC). The DGCs recorded have a long flutter period consisting of miniature ventilations, and 29-48 % of the total CO₂ output occurred during this period. In this study, the flutter period played an important role in the modulation of metabolic rate, in contrast to other studies in which the burst period has been shown to be important. We suggest that the long flutter period is important in reducing respiratory water loss in arid-dwelling arthropods. This study lends support to the hypothesis that discontinuous gas exchange is important in reducing respiratory water loss from beetles that need to minimise dessication because of the high water vapour pressure gradient they experience. If the use of underground burrows were responsible for the evolution of discontinuous gas exchange, then we would expect all nine tenebrionid species to use DGCs since both the nocturnally and diurnally active species bury in the sand during periods of inactivity. We conclude that the activity patterns of the beetles are more important than their habitat associations in designating the type of respiration used.