Desert geckos glow neon green in the moonlight, scientists discover

January 12, (Agencies) | Publish Date: 1/12/2021 10:53:05 AM IST

 A desert gecko from Namibia has brilliant glow-in-the-dark markings that shine neon green by the light of the moon. The mechanism that produces its glow has never been seen before in land animals with backbones.

Web-footed geckos (Pachydactylus rangei) have translucent skin with large, yellowish markings: stripes on their sides and rings surrounding their eyes. But those markings light up brightly when they absorb the moon's bluer light.

Fluorescence — when light is absorbed and then emitted at a longer wavelength — has been found in other reptiles and amphibians, produced by their bones or by chemical secretions in their skin. However, web-footed geckos generate their light using skin pigment cells that are filled with guanine crystals. These cells, called iridophores, have previously been linked to color display in geckos and lizards, but this is the first evidence that they also enable geckos to glow in the dark.

Web-footed geckos, which live in dry riverbeds and dunes in the Namib desert, measure about 4 to 6 inches (10 to 15 centimeters) in length, according to Animal Diversity Web (ADW), a wildlife database maintained by the University of Michigan's Museum of Zoology. The geckos use their large, webbed feet to burrow through fine sand, and they are mostly active at night, ADW says.

In 2018, the study authors had found that chameleons have bones that glow through their skin. That discovery prompted the scientists to look for hidden glows in other reptiles and amphibians, said study co-author Mark Scherz, a postdoctoral researcher with the Adaptive Genomics Group at Universität Potsdam in Germany.

David Prötzel, lead author on this study and a doctoral candidate at the Bavarian State Collection of Zoology (ZSM) in Munich, kept P. rangei geckos at home, and got "an incredible surprise" when he shone a UV light on his web-footed geckos and discovered that they glowed neon green, Scherz told Live Science in an email. The researchers then tested 55 P. rangei specimens from ZSM under UV light, finding evidence of fluorescence in adults of both sexes and in juveniles.

In other fluorescent amphibians, such as the polka-dot tree frog (Boana punctata), the glow comes from a chemical that circulates through its lymph system. And reptiles such as chameleons and saddleback toads in the Brachycephalus genus display fluorescent bones through body regions where their skin is very thin. 

"Actually it turns out quite a few other species, including geckos, have sufficiently transparent skin that their bones' fluorescence can be seen through it under a sufficiently strong UV light," Scherz said.

But in the web-footed geckos, the bright neon-green glow came from iridophores. Though iridophores were not previously associated with fluorescence in geckos, they are known to fluoresce in some species of reef fish, according to the study. The web-footed gecko is the first known gecko to possess two types of iridophores: one that fluoresces, and one that doesn't.

(Live Science)

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