Did you know, there's a species of semi-aquatic lizard from the tropical forests of southern Costa Rica that produces a large bubble over its nostrils, allowing it to breathe underwater?
The lizard in question is a water anole (Anolis aquaticus). For some time, scientists have known about the little lizard's ability to 'scuba dive', but they didn't know why it was doing it.
Now, a team of researchers from the Binghamton University in New York think they have found the answer.
“We know that they can stay underwater for a really long time," says Lindsey Swerk, an assistant research professor of biological sciences at Binghamton University. "We also know that they're pulling oxygen from this bubble of air.”
“We didn’t know whether there was actually any functional role for this bubble in respiration. Is it something that lizards do that is just a side effect of their skin’s properties or a respiratory reflex, or is this bubble actually allowing them to stay underwater longer than they would, say, without a bubble?”
To investigate whether the bubble has a purpose in respiration or is merely a byproduct of breathing, Swierk applied a substance to the surface of the lizards' skin that would prevent bubbles from forming.
“Lizard skin is hydrophobic. Typically, that allows air to stick very tightly to the skin and permits this bubble to form. But when you cover the skin with an emollient, air no longer sticks to the skin surface, so the bubbles can't form,” explains Swierk.
Swierk counted the number of bubbles that the lizards produced and the time they could remain underwater, then compared these results to a control group of lizards that breathed normally.
She found that the lizards in the control group could stay underwater 32% longer than those with inhibited bubble formation.
“This is really significant because this is the first experiment that truly shows adaptive significance of bubbles. Rebreathing bubbles allow lizards to stay underwater longer. Before, we suspected it – we saw a pattern – but we didn't actually test if it served a functional role,” says Swierk.
Having established that the bubble helps lizards stay underwater for longer periods, Swierk then wanted to find out why spending more time beneath the surface is an advantage.
The leading theory is that being underwater keeps the water anoles safe from predators.
“Anoles are kind of like the chicken nuggets of the forest. Birds eat them, snakes eat them.” says Swiek.
“So by jumping in the water, they can escape a lot of their predators, and they remain very still underwater. They're pretty well camouflaged underwater as well, and they just stay underwater until that danger passes. We know that they can stay underwater at least about 20 minutes, but probably longer.”
There is much more to learn about the lizards, says Swierk, who plans to figure out whether they are using the bubbles as something known as a physical gill – a feature used in insects that helps them breathe underwater.
Alexandra Martin, one of Swierk’s graduate students, is testing whether this physical gill-type action is allowing the lizards to spend even more time beneath the surface by changing the oxygen levels of the water around them.
The paper, Novel rebreathing adaptation extends dive time in a semi-aquatic lizard, was published in Biology Letters.
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