This mechanism for generating light has never been seen before in terrestrial vertebrates.

The Palmetto Gecko (Pachydactylus rangei) has translucent skin with large yellow markings: stripes on the sides and ring around the eyes. But these areas light up as they absorb the Moon’s bluer light.

Fluorescence has been found in other reptiles and amphibians, either by their bones or by chemical secretions on their skin. The Palmetto geckos, however, have membranes that produce their light using pigmented skin cells filled with guanine crystals. These cells, called iridophores, were previously as‌sociated with color rendering in geckos and lizards, but this is the first evidence that they also allow geckos to glow in the dark.

Palmetto gecko is about 10 to 15 cm long. These geckos use large webbed feet to pass through fine sand and they are mostly active at night.

In 2018, study authors discovered that chameleons have glowing bones through their skin. Study co-author Mark Scherz, at Potsdam University, Germany, said the discovery prompted scientists to look for hidden light in other reptiles and amphibians.

David Protzel, the lead author of this study in Munich, raised the Palmetto gecko at home and made a surprising discovery of shining UV lights on his geckos.

The researchers then examined 55 samples of the Palmetto gecko under UV light and they found evidence of fluorescence in both male and female geckos.

"In fact, it turns out that quite a few other species, including geckos, have skin transparent enough to see the fluorescence of their bones under strong enough UV light," Scherz said.

Yellowish-yellow stripes on the sides of the gecko are visible to other geckos, but are obscured from predators attacking from above.

But in the Palmetto gecko, bright neon green light comes from the keratinocytes. Although iridophores were not previously as‌sociated with gecko fluorescence, they are known to fluoresce in some coral reef fish species. The Palmetto gecko is the first known gecko to possess two types of epidermal cells. In it there is a luminescent type and a non-luminescent type.

The light these cells produced was brighter than the light emitted by the chameleon bones and was one of the brightest examples of fluorescence in terrestrial animals, the study authors said.

Such glowing signs along the lower body and around the eyes would be very visible to other geckos, but would be obscured from predators with higher vantage points, such as owls. or jackal.

Although scientists don’t know how most animals use their fluorescence, the location and brightness of these markers, as well as their visibility in the dry desert environment. The gecko, where there is not much vegetation, suggests that fluorescence plays a role in the gecko’s social interactions.

"We have observed that in captivity, even though these animals are largely solitary, they still run close to each other to greet each other after a short separation. They also lick the steam that remains on top of each other. So there are many reasons to be able to see each other at a long distance that would be very useful for these geckos, "Scherz said.