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Some beetles somehow manage to breathe under water, but how?

Posted April 14, 2019

Our world is full of life. You can look up in the sky or under your feet – there is life everywhere. But some creatures are confusing scientist. For example, diving beetles stay under water for quite some time, but how do they breathe? Researchers from the University of Adelaide think that they finally solved this mystery.

Diving beetles are able to absorb oxygen directly from the water, but that’s not an easy task. Image credit: Sandy Rae via Wikimedia (CC BY-SA 3.0)

Tiny diving beetles found in aquifers in the Western Australian goldfields pretty much never surface to breathe. In fact, when scientists wanted to study several of them, they encountered a bit of a problem. They had to drill into the aquifer and drop small plankton into it in order to collect some animals in a small vial. Scientists compare this process to walking in a dark forest with a torch – you can only see what is right ahead of you. And there are plenty of scary pale-coloured eyeless creatures zipping around. But how do they breathe? Do they breathe at all?

This question is not that simple. Normally beetles collect a bubble of air and then go underwater. But these ones do not even have such luxury. Scientists manoeuvred a tiny oxygen sensor against the body of submerged beetles that they caught. Then they moved these sensors away little by little recording oxygen levels as they were withdrawing from these beetles. Scientists found that the oxygen levels in the water next to the beetles were significantly reduced. This means that the beetles were breathing, but not in the way we think they should – they are absorbing oxygen directly from the water. Researchers think that a process called cutaneous respiration is in play in this situation – insects absorbed oxygen directly from the water.

Interestingly, these insects evolved in terrestrial environment. This is clear because of their gas-filled respiratory system. However, some of the beetles became aquatic and had to evolve their respiratory systems to a completely different direction. No air bubbles for them. Karl Jones, lead author of the study, said: “‘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”.

It is quite fascinating how precise this mechanism has to be to work. Just small discrepancies would mean that diving beetles won’t be able to breathe underwater. In that case they would have to evolve new features or simply not live in such environments.


Source: University of Adelaide

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