Respiratory patterns and metabolism in tenebrionid and carabid beetles from the Simpson Desert, Australia

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The respiratory physiology of four species of Australian desert-dwelling beetle was examined using a flow-through respirometry system over the temperature range of 20-40°C. The two species of tenebrionid beetles (Heleus waitei and Pterohelaeus sp.) did not exhibit the discontinuous gas exchange cycles (DGC), a mechanism to possibly reduce respiratory water loss rates, observed in other arid-dwelling beetles. There were small increases in metabolic rate with temperature resulting in a Q 10 of 1.84 for H. waitei and 1.99 for Pterohelaeus sp. Furthermore, H. waitei has no increase in metabolic rate over the temperature range 25-35°C (Q 10=1). The two species of carabid beetles (Cerotalis sp. and Carenum sp.) displayed the DGC respiratory pattern, having long flutter and burst periods. Both species also exhibited spiracular movement or muscular pumping in the burst period. Relatively low Q 10 values of 1.31 and 1.64 were measured for Cerotalis sp. and Carenum sp., respectively. Cerotalis sp. had no increase in metabolic rate over the temperature range 20-35°C (Q 10=1). In both species the temperature-associated increases in metabolic rate were modulated by increases in DGC frequency. All the four beetle species studied have fused elytra, a closed subelytral cavity and are nocturnally active, which should assist in reducing respiratory water loss rates, and occupy similar microhabitats. Thus we propose that the difference in respiratory patterns found between the tenebrionid and carabid beetles is related to their thorax morphology, food type and food availability.