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Fish-scale gecko in Madagascar evades predators by getting naked

Fish-scale gecko in Madagascar evades predators by getting naked
The newly discovered fish-scale gecko in Madagascar, Geckolepis megalepis, has the largest scales of any gecko in its genus, a new study finds. (F. Glaw)

Talk about escaping by the skin of your teeth! Scientists have discovered a new type of gecko — an evasive little lizard who can escape predators' grip not just by dropping its tail, but by shedding the scales on its skin.

The new species Geckolepis megalepis, described in the journal PeerJ, has big, fish-like scales, larger than any of the other gecko species in its genus. It's also the first new Geckolepis species to be described in 75 years, and the first currently recognized species in 123 years.

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G. megalepis lives in northern Madagascar, where it appears to be found only around the limestone karst of the Ankarana massif. While other geckos do have scales that can slip off passively, Geckolepis seems to have a certain amount of control over the process.

"It seems to be a very extreme behavior in living geckos," said study coauthor Juan Diego Daza, a herpetologist at Sam Houston State University in Huntsville, Texas.

This has created problems for scientists trying to study the genus Geckolepis; capturing the lizards without losing their scales in the process has been a total pain for more than 120 years.

"Indeed, the process of collection often damages even the most intact specimens," the study authors wrote. "Voeltzkow (1893) captured his specimens with bundles of cotton ('Wattebäuschen'), and even this was not sufficient to prevent some scale loss."

Among its scale-shedding brethren, however, G. megalepis's scales are king. The oversized scales seem to come off at the slightest perturbation, leaving smooth, pink skin beneath.

When grasped by a predator, fish-scale geckos lose their scales and the skin underneath, a bizarre behavior important in helping them escape.
When grasped by a predator, fish-scale geckos lose their scales and the skin underneath, a bizarre behavior important in helping them escape. (F. Glaw)

These scales can be torn off so easily partly because of their size, the scientists said. Bigger scales have much more surface area relative to the edge where they're attached to the skin than smaller scales do, which makes them easier to rip away.

But the scientists think there's also a control mechanism at play, in which the gecko contracts a layer of connective tissue beneath the skin to help release the scales, and the skin's uppermost blood vessels are squeezed to prevent bleeding.

How and why this particular group of geckos developed this trait remains a mystery, Daza said. Their scales aren't just made of keratin (the kind of protein found in teeth and nails) – they also have some bone in them, which is more costly for living things to produce. So when a gecko drops its scales, it's forfeiting a pretty heavy energetic investment. The lizard might also risk dehydration, if the scales were also helping its body retain water.

A partly naked gecko looks kind of like a half-picked scab, but at least the look doesn't last forever.

"The scarless regeneration of the whole integument occurs within a few weeks, apparently starting from stem cells of the deeper layers of the connecting tissue and is considered as unique among vertebrates," the study authors wrote.

That stem-cell-fueled regenerative power could be of interest to scientists studying applications in human medicine.

Scientists think that these scales are meant as a defensive measure, but they've only documented their use as a means of escape a handful of times in the literature: from a scorpion (Grosphus flavopiceus), a bird (Dicrurus forficatus) and a large nocturnal Blaesodactylus gecko. For that last case, the G. megalepis lizard actually slipped out of the predator's mouth about 30 seconds after it had been caught.

"The predator, or whoever it is, is left with a mouthful of scales – and the animal escapes," Daza said.

Perhaps these slippery little lizards could teach Houdini a thing or two. In the meantime, scientists say they hope to keep studying how this remarkable gecko skin works, and what's driving the evolution of these extra-large scales.

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For now, however, Daza said he was concerned for the immediate future of these species, many of whom are under stress due to habitat loss.

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UPDATES:

Feb. 8, 8:35 p.m.: This story was updated with comment and context from study coauthor Juan Diego Daza.

This article was originally published Feb. 7 at 5:45 p.m.

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