Anoles are an extremely successful family of lizards, with more than 400 species. They are found throughout the warmer regions of the Americas, almost anywhere you care to look. From urban shrubberies and gardens to wild, tangled, tropical forest, you will find an anole somewhere, hunting insects or sipping nectar from flowers.
These small lizards are easily overlooked. Many are brown or green, with bands and spangles of contrasting markings, and they are on the slim side, too – twiggy lizards in a world of twigs. The only time they catch the eye is when the males of some species flash a brightly coloured chin flap, called a dewlap, at each other and potential mates.
Several species are closely associated with fresh water. The water anole (Anolis aquaticus) – whose name says it all – is one of these, never straying far from forest streams. Here, it makes an understated living, skittering after insects among a tangle of riparian roots, stems, leaves and rocks.
Never reaching more than 7cm (excluding the tail), water anoles find themselves on the menu for birds, snakes and mammals – I’ve even found them tangled in the webs of orb spiders.
How anoles are able to breathe underwater
Other than lightning agility and exceptional camouflage, it turns out that these marvellous little lizards have yet another cunning way of evading capture that has only recently come to light.
Dropping into the water is a common strategy in nature; many frogs do it, green iguanas do it, even pythons and nestling hoatzin birds do it. What sets the anole apart is that it can extend its subaquatic stay by more than a quarter of an hour by breathing underwater – or more accurately, re-breathing.
The moment the water anole submerges, it transforms into a mercurial lizard, enshrouded in a thin layer of air due to the rough texture and waterproof nature of its scaled skin. But it’s what happens next that is the really surprising bit.
A bubble appears at the top of the head, over the snout. It expands, stretches, connects with the rest of the air pocket surrounding its body, and is then sucked back into the anole’s nostrils. Not one bubble escapes to the surface.
When a living creature inhales, oxygen enters the body and carbon dioxide, the waste product of our metabolism, is exhaled.
However, not all the oxygen is extracted in each breath, so some remains in the exhalation. The water anole’s air pocket allows it to recycle this ‘missed’ oxygen. Some anoles will do this dozens of times in a single dive, recycling the air in the pocket and using the oxygen within.
It is also likely that due to the highly soluble nature of carbon dioxide and, to an extent, oxygen in water, the large surface area of the thin layer of air surrounding the anole also acts as a ‘plastron’ or physical gill, with carbon dioxide leaving the system and dissolving in the surrounding water, and oxygen the reverse.
All of which enables the anole to sit it out at the bottom of the stream for a short spell until the threatening predator has moved on.
Illustration: Peter Davis Scott/Art Agency