Chameleons are small to mid-size tree-dwelling reptiles that are famous for their ability to change colors. A team of researchers from Germany has now discovered that the crests and tubercles on the heads of many chameleon species emit blue fluorescence when illuminated with ultraviolet (UV) light. A paper reporting this discovery is published in the journal Scientific Reports.
The panther chameleon shows fluorescent crests on the head. Image credit: David Prötzel, ZSM & LMU.
Fluorescence is widespread in marine organisms but uncommon in terrestrial vertebrates.
“So we could hardly believe our eyes when we illuminated the chameleons in our collection with a UV lamp, and almost all species showed blue, previously invisible patterns on the head, some even over the whole body,” said co-author David Prötzel, PhD student at the Bavarian State Collection of Zoology.
Chameleons have conspicuous bony crests and tubercle pattern on their heads. The shape, size and distribution of these crests are taxonomically informative and sexually dimorphic.
To investigate the properties of these tubercles, Prötzel and co-authors used a variety of modern methods.
Micro-CT scans showed that the pattern of fluorescence exactly matched the distribution of tubercle pattern on the skull.
“The tissue analyses yielded another surprise,” said co-author Dr. Martin Heß, from the BioCenter of Ludwig-Maximilians-Universität in Munich.
“Our histological 3D reconstruction shows that the skin covering the tubercles on the skull is very thin and consists only of a transparent layer of epidermis.”
“These patches effectively act as windows that enable UV light to reach the bone, where it is absorbed and then emitted again as blue fluorescent light.”
“It has long been known that bones fluoresce under UV light, but that animals use this phenomenon to fluoresce themselves has surprised us and was previously unknown,” said study senior author Dr. Frank Glaw, Curator of Herpetology at the Bavarian State Collection of Zoology.
The tubercles fluoresce under UV light to form distinct patterns that represent certain chameleon species or species groups.
In addition, the males in most species of the genus Calumma have significantly more fluorescent tubercles than the females.
“We suspect that this fluorescence is not a mere coincidence, but helps the chameleons to recognize conspecifics, and presents a consistent pattern in addition to their skin-based color language — especially as blue is a rare color and easily recognizable in the forest,” the researchers concluded.
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David Prötzel et al. 2018. Widespread bone-based fluorescence in chameleons. Scientific Reports 8, article number: 698; doi: 10.1038/s41598-017-19070-7
