Fluorescent pattern of the chameleon Calumma globifer from Madagascar. The animation shows the inconspicuous tubercles in sunlight, the fluorescent pattern under UV light, and the underlying bone tubercles, which are based on a micro-CT model of the skull.Credit: Animation: David Prötzel (ZSM/LMU)
Chameleons are known to communicate with conspecifics by altering their surface coloration. Munich researchers have now found that the bony tubercles on the heads of many species fluoresce under UV light and form impressive patterns.
Biogenic fluorescence is mainly known from marine organisms, but is rare 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," says David Prötzel, lead author of the new study and PhD student at the Bavarian State Collection of Zoology (ZSM).
To understand the phenomenon, the researchers used a variety of modern methods. Micro-CT scans showed that the pattern of fluorescence exactly matched the distribution of tubercles pattern on the skull. The tissue analyses yielded another surprise: "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,"explains Dr. Martin Heß from the BioCenter of Ludwig-Maximilians-Universität (LMU) in Munich. 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.
David Prötzel, Martin Heß, Mark D. Scherz, Martina Schwager, Anouk van’t Padje, Frank Glaw. Widespread bone-based fluorescence in chameleons. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-017-19070-7
