Water lizards, semi-aquatic lizards smaller than a pencil, are highly sought after as snacks by predators in the rainforests of Costa Rica and Panama. Preyed on by snakes, birds, small mammals, and large lizards, the lizards hide in vegetation along rocky riverbanks. When faced with danger, the lizard dives into the water and produces a bubble behind its nose that allows it to stay underwater for up to 20 minutes, or possibly longer.

Lindsay Swirk, a behavioral ecologist at Binghamton University in New York, worked with Luke Mahler and Chris Boccia of the University of Toronto and other researchers to document the diving abilities of aquatic anoles. The purpose of the underwater stunts was unclear.

Swierk wasn't sure whether the adaptation was a survival function or just a weird side effect of its water-repellent skin. Although water can't stick to a lizard's skin, its structure allows air bubbles to form around body parts.

Swirk discovered that the bubble allowed the little lizard to stay underwater for much longer than would have been possible. The results were published in the journal Biology messages.

Using an underwater camera, Swirk first saw the bubble appear and disappear above the lizard’s snout. The bubble, which is formed mainly by air stored in the lizard’s lungs but also from air pockets in its waterproof skin, collects above the snout so that the animal can breathe air again underwater. “There are attachment points in the head where the bubbles appear to be attached,” Swirk said.

The scientists followed 28 lizards collected from a tropical forest in southern Costa Rica. Half were smeared with body lotion (a daily moisturizer) to keep the bubbles from sticking to their skin. The other half received a little water to keep their hydrophobic skin intact and allow natural blister formation.

Lizards with intact bubbles dived 32% longer than lizards with poor bubble production. When lizards couldn't breathe air inside the bubble, they couldn't dive as long.

However, diving with lizards is a last-resort behavior. It’s not something the species uses very often, said Kurt Schwenk, an evolutionary biologist at the University of Connecticut who was not involved in the study. Aquatic anoles are cold-blooded and regulate their temperature according to their environment. When they dive into a cold current, it takes time for them to warm up again.

Time in the sun takes time away from other important tasks for lizards, such as hunting or defending their territory. Previous research has shown that male lizards, which are responsible for defending their territories, come out of the water early because they can't risk hypothermia. “Being cold makes them slow down and have a poor metabolism,” Schwenk said.

Although this is the first vertebrate to produce bubbles for underwater breathing, it is a behavior found in small aquatic insects such as alkali flies and diving beetles, as well as some spiders.

Water spiderArgeronita Aquatica) It uses an equally bizarre mechanism to breathe underwater. It forms an air bubble trapped in the water-repellent hairs around its abdomen, allowing it to live almost entirely underwater, emerging for air every 24 hours. The bubble brings in oxygen and expels carbon dioxide. In future research, Swierk is interested in seeing if aquatic anoles can do the same.

It's a behavior of clear evolutionary significance, and provides an unlikely refuge for species that almost all rainforest animals like to eat.

“This is a great example of how evolution works to help animals adapt to all sorts of strange environments and find interesting solutions to problems,” Swierk said.