Some lizards can stay underwater for longer by blowing out and then rebreathing bubbles of air. This has been suspected since the behaviour was first observed, and now experiments have confirmed it.
While doing fieldwork in Costa Rica in 2015, Lindsey Swierk at Binghamton University in New York State noticed that some lizards (Anolis aquaticus) dived into streams as people approached and stayed underwater for long periods. When her team filmed the lizards underwater, they noticed they blew out large bubbles from their nostrils that remained attached to their heads, and then breathed them in again.
Swierk wrote a short paper describing the behaviour in 2018. In 2021, she and her colleagues reported that at least 18 species of Anolis lizards rebreathe bubbles while underwater, and that they can stay underwater for up to 18 minutes.
These species all have water-repellent skin that remains covered by a thin layer of air when they are underwater, giving them a silvery appearance. This is also why the larger bubbles they blow out remain attached.
Now Swierk has done a further study in which she applied a kind of moisturiser known as an emollient to the heads of newly caught lizards with a paintbrush, to temporarily stop the skin repelling water.
These lizards could only blow out tiny bubbles. “They were able to rebreathe a little because I did not apply the emollient over the nostrils, for obvious reasons,” says Swierk.
The lizards were then put in a clear plastic tank filled with stream water to see how long they could stay underwater, before being released. Those painted with plain water stayed underwater 32 per cent longer on average than lizards painted with the emollient.
Swierk thinks simply rebreathing the same air allows the lizards to get more oxygen out of it. In addition, as the blown-out bubble joins up with the thin layer of fresh air on the skin of the lizard, more oxygen will enter the bubble. In other words, the thin layer of air on the skin might act as a scuba tank.
What’s more, it is also possible that the large bubble acts as a gill, allowing carbon dioxide to dissolve out into the water and oxygen to diffuse in. It is known that many insects, spiders and plants can survive underwater thanks to layers of air that act as gills.
The star-nosed mole and the water shrew also blow out and rebreathe bubbles underwater, but they are thought to do this as a way of smelling while submerged.
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