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A lizard that lives next to streams in the mountains of Costa Rica appears to have evolved a kind of scuba tank to help it stay underwater for long periods. It can remain submerged for at least 16 minutes, and blows out and re-inhales a large bubble of air while underwater.

This extraordinary behaviour has been by ecologist Lindsey Swierk of Binghamton University, New York. Her footage shows that there are pockets of air adhering to the head and body of the lizard when it is underwater.

By breathing out a big bubble that envelops these air pockets and taking it back in, Swierk thinks the lizard may be extracting the oxygen from the pockets. “They are probably extracting lower concentrations of oxygen every time they’re respiring the air bubble, but it might just be enough to keep them underwater for long enough that they can escape a threat,” she says.

Big bubble

Even though the bubble is relatively large, it remains attached to the lizard’s head rather than floating off to the surface. “The bubble is pretty huge,” says Swierk. “The shape of the head could be an adaptation to hold the air bubble in place.”

Several aquatic insects and spiders have special adaptations that allow them to take bubbles of air underwater. In some cases, it has been shown that these bubbles actually function as gills — oxygen diffuses into the bubble from the surrounding water while carbon dioxide diffuses out.

They don’t allow animals to stay underwater indefinitely, however, as the bubbles shrink as the nitrogen in them dissolves into the water.

Diving into streams

It is possible that the lizard’s bubble functions as a gill too, says Swierk, but she is not convinced this is the case. She is now looking for collaborators to carry out further studies.

Swierk first noticed the lizards (Anolis aquaticus) in 2015 while walking near mountain streams in Costa Rica. “They would jump into the water as we approached.”

Her team also noticed they would sometimes dive and remain underwater for long periods. Analysis of their stomach contents revealed that some were feeding on insects found almost exclusively underwater.

So Swierk bought an underwater camera to see what they were doing. She has not seen the lizards catch any prey underwater, but did record the bubble-blowing.

There is little doubt that the lizards swim and dive to avoid predators like birds. The longest dive the team has recorded so far is 16 minutes – and that individual swam away after they disturbed it. So it’s possible they can remain underwater even longer.

A short report describing the behaviour will appear in the journal Herpetological Review.

Many amphibians can absorb oxygen from water through their skins, but there is no reason to think these lizards can do this, Swierk says.