When water's scarce, every drop counts. Desert insects are masters of water conservation, sealing up orifices and developing internal reservoirs. But they risk losing precious liquid with every breath they take. Some desert insects protect themselves from desiccation by breathing in through thoracic spiracles and out of their abdominal spiracles. But do all desert species breathe this way to conserve water? Marcus Byrne wasn't sure, but knew that understanding how Circellium bacchus breathes was vital if he was going to understand the ecology of this endangered species. He teamed up with an ant respiration specialist, Frances Duncan, to investigate how the enormous beetles breathe in and out. But when they measured the exhaled gases from the front and back halves of the insect, the scientists realised that these dung beetles weren't using the back spiracles at all, they were breathing out through a single front spiracle alone()!
To these flightless dung beetles, elephant dung balls are everything; from larders and incubators, up to nuptial offerings during their mating rituals. So each ball of elephant waste represents a significant investment for each beetle. One of the beetle's major concerns is conserving water while they toil over their dung ball. Perceived wisdom held that other beetles protected themselves from desiccation by breathing infrequently, passing the air through a humid cavity created by the redundant wing covers before exhaling carbon dioxide out of the posterior spiracles. Byrne and Duncan decided to check whether their dung beetles did the same.
Duncan scaled up a respirometry technique that she usually uses on smaller creatures by using a large Perspex box, instead of a small syringe, for a respiration chamber. By fitting a rubber skirt around the beetle's waist and dividing the chamber in two, the two scientists isolated the gases exhaled from the front and back ends of the beetle. After leaving the insect to breathe overnight they checked both chambers and discovered that all of the exhaled carbon dioxide was unexpectedly in the front half of the respirometer!Duncan remembers that at first everyone was sceptical, but after testing every possible permutation of insect orientation in the breathing chamber and double-checking by using oxygen as the tracer gas, no one could argue, the beetles were exhaling from the front two spiracles alone.
Focusing on the insect's thoracic spiracles, Duncan attached a tiny tube over each spiracle and recorded the exhaled breath. After testing three beetles they realised that the insects were exhaling through one spiracle alone, the right one! Byrne admits that he was `blown away' when they realised that the insects were right-handed breathers.
Duncan and Byrne suspect that this is a deliberate strategy to conserve water, allowing the insects to seal the elytral cavity and limit water losses by exhaling through a single spiracle. Having turned insect respiration on its head, they need to solve the next puzzle; how the beetles circulate each breath around their bodies before they breathe out.
