Namib Sand Geckos: these geckos have biofluorescent markings that produce a neon-green glow when exposed to the moonlight
Pachydactylus rangei, commonly known as the Namib sand gecko, is a unique type of lizard that can be found only in the Namib Desert, which stretches across Namibia, Angola, and South Africa. This species is especially common along the arid coastal region known as the Skeleton Coast.
Above: Pachydactylus rangei
This is one of the only geckos in the world that is known to have fully-webbed feet; the unique morphology allows the gecko to run atop the sand and dig beneath the dunes, and it's able to escape from the blistering heat of the desert by burrowing down into the sand during the day and then emerging only at night, when the temperature finally drops.
Above: a close-up of the gecko's webbed foot
Namib sand geckos are covered in translucent scales, but their bodies often have a strangely colorful appearance, because their circulatory system, spinal column, internal organs, and optical membranes are partially visible through their skin. Those underlying structures produce various shades of pink, blue, purple, orange, and yellow.
Above: the colorful appearance of Pachydactylus rangei
These geckos also have very distinctive markings that fluoresce when exposed to UV light (including moonlight) which causes them to emit a bright, neon-green glow. The fluorescent dermal markings are unique to this species, and Pachydactylus rangei is the only terrestrial vertebrate that is known to have an iridophore-based form of biofluorescence.
Above: the patterns glowing under UV light
Researchers believe that the biofluorescent markings might allow the geckos to locate one another in the vast, desolate expanse of the desert, as this article explains:
The fluorescent areas of Pachydactylus rangei are concentrated around the eyes and along the lower flanks. This positioning is practically invisible to predators with a higher perspective (e.g. birds and jackals) but highly conspicuous from a geckoâs perspective. As Pachydactylus rangei is sociable but generally solitary, and occurs at low population densities, such a signal might serve to locate conspecifics over greater distances.
Above: a Namib sand gecko licking drops of condensation from its face and eyes
These lizards obtain moisture by licking the condensation that forms on their own bodies and on the bodies of other geckos, and they've been known to engage in social behavior with other members of the same species:
Encounters in Pachydactylus rangei might serve purposes beyond mating opportunities: as the Namib desert has extremely low precipitation, fog is a key water source for its flora and fauna. Fog condenses on the bodies of the geckos, and they lick it from their faces. In husbandry, we have observed individuals licking water from conspecifics, taking advantage of a much greater available surface area.
Additionally, after short periods of isolation, the geckos run to meet each other. The combination of vital hydration with socialisation might reinforce signals that enable such meetings, and the cost of visibility to predators with higher vantage points, might constrain the signals to regions best visible from eye-level and below.
Above: the photo at the top shows a Namib sand gecko emerging from its egg, while the photo on the bottom shows a freshly-hatched gecko screaming at the universe
Namib sand geckos can produce complex vocalizations, including squeaks, clicks, croaks, and barks, especially when they're startled, threatened, or attempting to attract a mate.
Above: close-up of Pachydactylus rangei
This species is also known as the web-footed gecko, Namib dune gecko, or palmatogecko.
National Geographic: The Web-Footed Gecko
Animal Diversity Web: Pachydactylus rangei
Scientific Reports: Neon-Green Fluorescence in the Desert Gecko Pachydactylus rangei Caused by Iridophores
Tropical Zoology: Substrate Excavation in the Namibian Web-Footed Gecko and its Ecological Significance
Journal of Arid Environments: The Lizard with Kaleidoscope Eyes: Population Characteristics of the Namib Web-Footed Gecko, Pachydactylus rangei
Snakes and Other Reptiles and Amphibians: Web-Footed Gecko
Dr. Mark D. Scherz: A Neon-Green Glowing Gecko
Australian Geographic: Skeleton Coast: Namibia's Strange Desert Dwellers