Respiratory strategies of tenebrionid beetles in arid Australia: does physiology beget nocturnality?

Abstract The respiratory patterns and role of mesothoracic and abdominal spiracles in gas exchange are examined using flow‐through respirometry in three species of Heleini beetles from the Simpson Desert, central Australia. Two species, Helea (Heleus) waitei and Helea sp., show a form of continuous respiration with 70% and 75% of the CO₂ being emitted from the mesothoracic spiracles, respectively. Their mass specific metabolic rates are similar and similar to other nocturnally active desert‐dwelling tenebrionid beetles. Brises blairi also shows a continuous form of respiration, with 66% of CO₂ being emitted from the mesothoracic spiracle but has a significantly higher mass specific metabolic rate. Unusually for arid‐dwelling tenebrionid beetles, all three of the study species are confirmed to be exclusively nocturnal. There is no evidence that this activity pattern is driven by current ecological factors, such as competition or predation, and it is proposed instead that nocturnality arises from physiological constraint. Heleini probably evolved under mesic conditions and lack some of the key physiological adaptations to reduce water loss that characterize day‐active tenebrionid beetles in arid environments elsewhere. In consequence, they are able to exploit arid conditions only by restricting their activity to the most benign phase of the 24‐h cycle.