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Suck it up: thorny dragons use their skin like a straw to drink water

New research shows spiky reptiles’ mouths cannot lick up water so they shovel damp sand on to their backs and suck moisture through their skin

Thorny devils feed almost exclusively on ants and their mouths have evolved to that specific purpose so instead take in water by using their skin like a straw. Photograph: Peter Walton Photography/Getty Images

Thorny devil lizards shovel damp sand on to their backs and suck the moisture using their skin, new research has found.

The spiky reptiles live in the arid deserts and sandy plains of central and western Australia, where they feed almost exclusively on ants. Their mouths have evolved to be specific to that purpose, to the point where they are unable to simply lick water from puddles or drops of condensation.

The lizards instead take in water by using their skin like a straw. Special structures allow it to collect water through its capillary channels in between the scales, and transport it – sometimes uphill – to the lizard’s mouth.

The mechanism works to acquire water through all possible sources in their desert habitat, such as by standing in puddles, dew, condensation and the occasional rain.

But the new research has suggested that thorny devils’ regular water intake comes from digging themselves into damp sand. The study was published on Thursday in the Journal of Experimental Biology.

Philip Withers, a professor of zoology at the University of Western Australia who co-wrote the study, said simply standing on moist sand did not allow the lizards to drink.

“They seem to shovel it on top of their back, which gives them gravity to help the water into their skin,” he said.

This seemed to be their most likely water source on a regular basis, along with rain.”

Withers clarified that the water had to be transported by their capillary channels – like “really, really small” aqueducts – to their mouth.

“Because they live in deserts, they have to have skin that’s really resistant to water loss – they can’t absorb water through their skin as well.

“The water gets sucked through the capillary channels that cover their entire body, it gets all the way up to the edge of their mouth, and they actually drink it …

“It’s like a sponge … When they close their jaws, it squeezes the water out.”

The thorny devils’ “skin blotting” technique was an evolutionary response to the demands of their habitat, Withers said. Horned lizards in the US had independently evolved similar characteristics.

Thorny devils had developed the sharp spines that coated their bodies to deter predators, allowing them to focus on eating ants.

“They’re so specialised for eating ants that they have teeny-tiny tongues and mouths,” he said. “They probably can’t drink water even if they tried.”

The lizards are widespread in hot and dry regions of Australia, although difficult to spot because of their excellent camouflage. “You can almost stand on top of one and not see it.”

The “weird, jerky motion” with which they walked was thought to mimic grass tussocks in the wind: “They look like a little wind-up toy.”

Withers said he had carried out most of the field work done on the species in the past 20 years, mostly because there were lots of them in his study area: “They’re so interesting; they’re really cool little animals.”

But they had not been studied at close quarters because of difficulties in keeping them in captivity.

“They’re hard to study in a laboratory because you’ve got to feed them tiny little ants, and lots of them,” he said.

Source: www.theguardian.com

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