Scientists have for the first time shed light on the illuminating ability of the UAE's desert-dwelling geckos to glow in the dark.
Three nocturnal species of the diminutive lizard, all common in sandy areas of the region, were found to have prominent skin fluorescence only previously seen in geckos in the sprawling Namib desert of Africa.
Researchers made the dazzling discovery during a field trip to a desert area of Sharjah in June 2022, and subsequently observed it in Al Ula in Saudi Arabia in April last year, in Nizwa, Oman, in May 2023, and in Sharjah, for a second time, in June.
The fluorescence is thought to enable the reptiles to see members of the same species, which may help the creatures mate with one another.
"One night we were looking with the UV light and we saw that actually these desert geckos were fluorescing. It was very surprising for us," Dr Bernat Burriel-Carranza, of the Museum of Natural Sciences of Barcelona and the first author of the study, said.
"It was an extremely bright neon-green colouration, similar to the one that had already been reported in Namibian desert geckos.
"Once we saw that was happening, in the other expeditions we were trying to focus on this and to find these specimens."
Light up the night
Bright fluorescence, often around the eye and on the flanks, was seen in two species, the dune sand gecko (Stenodactylus doriae) and the Arabian web-footed sand gecko (Trigonodactylus arabicus), both of which inhabit very sandy environments with little vegetation.
The eastern sand gecko (S. leptocosymbotes) also showed fluorescence, albeit less prominently, around its eyes and on its flanks, while a fourth species, Slevin’s sand gecko (S. slevini), had just a small amount around its eye.
Among the other authors of the study, published in the Journal of Arid Environments, is Johannes Els, of the Breeding Centre for Endangered Arabian Wildlife, part of the Environment and Protected Areas Authority, in Sharjah.
The fluorescence can be seen by humans only if a UV lamp is shone on the animals, but is probably visible to geckos without UV illumination because their eyes detect light outside of the human visible spectrum.
Fluorescence has previously been observed in six gecko species, but only one of these, the nocturnal web-footed gecko, found in the Namib desert in Africa, fluoresces from its skin.
These animals in the Namib desert fluoresce around their eyes and on their lower flanks, probably so the creatures can spot one another, allowing them to mate or to lick water that has condensed on each other’s bodies, a useful way to hydrate in a desert.
The nocturnal web-footed gecko’s ability to fluoresce is thought to have evolved separately from that of the geckos in Arabia.
"It seems that this type of mechanism can be very useful to communicate in deserts because they have evolved this fluorescence independently," Dr Burriel-Carranza said.
Wary of predators
That the skin fluorescence is found on the lower parts of the geckos’ bodies may be so that it is less visible to potential predators.
"Predators might also see UV light, so this is probably why they have it underneath or on their sides only and not on their back," Prof Salvador Carranza, of the Institute of Evolutionary Biology at CSIC-Pompeu Fabra University in Barcelona, the senior author of the study, said.
"There is a compromise between communication and also being attacked by other animals. Sometimes there is a trade-off."
If the animals are alarmed, they tend to press themselves against the ground and hide their flanks, indicating that the geckos are probably aware that these areas are more easily spotted by predators.
With some other geckos, the fluorescence comes from the bones, which show up because the animals’ skin is thin and translucent.
"It’s very clear when you see the bone is fluorescing, because you will see for example the ulna, the tibia, a specific bone," Dr Burriel-Carranza said.
Photographs taken as part of the latest study show, in addition to skin fluorescence, bone fluorescence in the tibia of the dune sand gecko.
While not confirmed from tissue studies, the geckos in Arabia that fluoresce from their skin are thought to do so thanks to iridophores, which are stacks of cells that give off light.
Prof Carranza said that the species in Arabia that have been found to fluoresce often live in remote desert areas that tend not to be developed.
They are classified, he said, as being of "least concern" by the International Union for Conservation of Nature, indicating that they are not threatened. They are different to the house geckos familiar to many UAE residents.
"Some of the animals that appear in the paper, they are some of the most common night geckos in the deserts of Arabia. You can find them everywhere from Saudi Arabia to Oman to the UAE," Prof Carranza said.
