Chameleons have long been regarded for their vibrant display of skin coloration and their incredibly adapted ways to signal social cues and communication. Now, scientists have discovered another trick tucked up the reptile’s sleeves – ahem, skin.
A new study has found that the small rounded projections on the bones around the face, known as tubercles, fluoresce blue under UV lights – basically, their bones glow in the dark. The tubercles come out of the bones of the skull and displace all but one thin layer of skin to create a sort of transparent “window” onto the bone.
In the world of fluorescence, it is common knowledge that bones react to UV light – just like your teeth at a blacklight rave – but in the case of chameleons, it is the first known instance of bone-based fluorescence in vertebrates, and the ability to potentially use it as a way to communicate.
"We could hardly believe it when we lit the chameleons in our collection with a UV lamp," said David Prötzel, first author of the study and doctoral student at the Zoological State Collection in Munich. "Almost all species showed blue, previously invisible patterns in the head area, some even distributed over the entire body."
The fluorescent property in bones is widespread in chameleons of Madagascar and Africa, who are able to do so with the help of proteins, pigments, chitin, and lymph. The fluorescent capabilities are mostly adapted in chameleons who live in forested, humid habitats with more ambient light as the blue fluorescence contrasts well to the green and brown forest color scheme.
The research, published in Scientific Reports, also opens new avenues in the study of how chameleons signal to potential mates and what exactly they find sexy.
The tree-dwelling lizards are sexually dimorphic, meaning males and females have different gender-driven characteristics that go beyond just sexual organs. Since male chameleons have more tubercles than females, scientists theorize the fluorescent dimorphism is a way to signal to the opposite sex that they're about to swipe left.
Little is known about the function or evolution of fluorescence in organisms, but scientists hypothesize it could be used as a way to protect themselves against excessive sunlight, hide from UV light detection, attract pollinators, scare off predators, recognize different species, or signal to potential mates that they’re picking up what the other is throwing down.
Fluorescence is common in marine organisms and more than 75 percent of surveyed deep-sea animals glow in the dark. What is less likely is that same fluorescence characteristics in “terrestrial tetrapods” (land-dwelling four-legged critters). It wasn’t until last year scientists discovered the first-known fluorescent polka-dot frog found in the Amazon.
While the study focused on one type of chameleon (Calumma), it suggests this characteristic is likely present in at least eight of the 12 chameleon genera. Noting the small sample size, researchers say they expect a greater sampling will only further strengthen the finding.