Mystery of submerged beetles’ breathing solved

The mystery of how aquatic beetles breathe in underground water has been solved by researchers from the University of Adelaide.

Studying tiny diving beetles found in aquifers in the Western Australian goldfields, scientists found that the insects absorbed oxygen directly from the water, with results published in the Journal of Experimental Biology.

Lead author Karl Jones, a PhD candidate from the University of Adelaide’s School of Biological Sciences, said discovering the beetles’ secrets had been an often fiddly endeavour.

“We dropped a small plankton net into boreholes drilled into the aquifer, and then pulled up the animals collected in a small vial at the bottom,’’ he said.

”Accessing the aquifers through these boreholes is like having a torch in a forest that is fixed in one position. You can only see the animals in your torch light, and you only get to see a very small part of the forest. However, it is a fascinating, almost alien-like world down there, with many pale-coloured eyeless creatures zipping about through the water.

“We then wanted to measure the oxygen concentration in the water immediately next to each insect’s body so we manoeuvred a tiny oxygen sensor against the body of submerged beetles and then slowly moved it away, in 50µm steps at first and then in 100 and 200 µm steps, recording oxygen levels as we went.”

Researchers discovered that the oxygen levels in the water next to the beetles was significantly reduced, a sign that they absorb oxygen straight from the water through a process called cutaneous respiration.

“Insects evolved in a terrestrial environment, as indicated by their gas-filled respiratory system, however several insect species have become aquatic secondarily, providing challenges for this system,’’ Jones said.

“Terrestrial diving beetles generally go to the surface and collect a bubble of air to take underwater but, with no obvious source of bubbles for subterranean beetles in their aquifer homes, we were unsure just how they breathed.

“But ‘breathing’ through the skin brings with it constraints and we found that the beetles – all know species of which are less than 5mm long – must be very small in order to live. Any bigger and the beetles’ surface area and thickness of their skin or exoskeleton would make it impossible to absorb enough oxygen to maintain their metabolic rate.”

Source: University of Adelaide