An exciting discovery was made by researchers who turned an ultraviolet (UV) torch to the web-footed gecko, Pachydactylus rangei. A paper published in the journal Scientific Reports details how the gecko, native to Namibia, exhibits neon-green fluorescence when under UV light. PhD students David Prötzel, Martin Heß, Frank Glaw, Martina Schwager, and Mark D Scherz made the discovery following a lengthy investigation into fluorescence in chameleons.

The discovery of the neon-glowing talents of web-footed geckos was something of a happy accident, as researcher and team member Prötzel had been keeping them at home for many years before he thought to point a UV torch at them. His fortuitous investigation revealed a big surprise: the geckos were glowing with bright neon-green stripes down their flanks and around their eyes.

The team wanted to establish how widespread this characteristic was among the web-footed geckos, so combined their findings with those taken from preserved specimens from museum collections. Their findings revealed that all members of the species glow and that the pattern is consistent between sexes. Interestingly, even hatchlings were found to possess a strong glow, demonstrating that this trait is something that develops while the gecko is still in the egg. Simple dissections and microscopy also showed that the fluorescence was skin-deep, and wasn't present in the scales that sit above it or the flesh underneath.

Using fluorescence microscopy, the researchers were able to establish that the areas that glowed were associated with guanine crystal granules. These granules were located within pigment cells known as iridophores, which are found in many animals and influence skin coloration. The geckos exhibited two layers of these iridophores, only the upper of which fluoresces. This is a curious observation for a reptile, as other than chameleons, most species within the group have just one class of iridophores.

“They do not, ordinarily, fluoresce, although there are fish in which they fluoresce red,” wrote co-author on the study Mark D Scherz, Universität Potsdam, in a statement. “Already it was clear that this was a completely new fluorescence mechanism for tetrapods.”

While the study has revealed a wealth of new information about the fluorescence of Pachydactylus rangei, the researchers express that there is still much to learn about these flashy reptiles and the source of their glow-up. The big question of “Why?” also still remains, with the researchers positing that the species may join other animals whose fluorescence, to date, has no clear function. Whatever the purpose (or lack thereof), it’s clear the web-footed gecko is a glowing example of fluorescence among vertebrates.

“When it comes to quantum yield, this is where the fluorescence of these geckos really shines (pun intended),” wrote Scherz. “With a yield of 12.5%, it is among the brightest vertebrate fluorescence known to date! Just as bright as the neon-green fluorescing frog, Boana punctata, which, however, fluoresces via an entirely different mechanism.

“All-in-all, we think web-footed geckos represent one of the best cases for functional significance of biological fluorescence in the animal kingdom. Although we have not yet had the budget or means to carry out behavioural experiments to formally test this biological role, we hope to be able to do this in the future, and also to carry out fieldwork to study their behaviour in situ. For now, though, we are just excited to finally reveal this awesome discovery to the world!”