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Chameleons not only change color, but their bones are fluorescent

Chameleons are known for their ability to change colors, something that lizards do mainly to communicate with others of their kind (and not to avoid predators, as commonly thought). But scientists have discovered that many chameleon species show another type of coloration: fluorescence.

It is known that there is a biogenic or bioluminescence fluorescence in a large number of marine animals, but that it is not common among terrestrial creatures. Chameleons are totally terrestrial animals, and therefore, the discovery of this trait among many species was a rather surprising finding. In an open access document published on Monday, German researchers said they found bony projections of fluorescent chameleon skulls under ultraviolet light.

"We could hardly believe in our eyes when we illuminated the chameleons in our collection with a UV lamp, and almost all species showed previously invisible blue patterns on the head, some even throughout the body", David Prötzel, lead author of the new study and Ph.D. student in the Bavarian State Zoology Collection (ZSM), said in a statement.

Bone projections, called tubers, absorb UV light and then emit it as fluorescence. This is possible because the skin on the tubers in the skull is extremely thin, effectively acting as an open window for UV light to pass through. The researchers analyzed this after the micro-CT scans showed an exact match between the fluorescence patterns and the tubers.

The skin of the chameleons is composed of multiple layers, with the upper layer transparent. Cells that change color are found in the lower layers of the skin. So the fact that the skin on the tubers acts as a window is not at all surprising, unlike the discovery itself.

"It has been known for some time that the bones emit fluorescence under UV light, but that animals use this phenomenon to fluoresce has surprised us and was previously unknown," Frank Glaw, curator of ZSM's herpetology and co-author, said in the statement. of the study.

This attribute was widespread among the chameleons of Madagascar and Africa, especially among genera that live in the forests. The humid forest habitat has a relatively higher component of ambient UV light, and the fluorescence is emitted in blue. Tubers that emit fluorescence under ultraviolet light are formed in patterns that are different between species or genera. Among the genus Calumma, males of most species have many more tubers than females.

The contrast of blue with predominantly green and brown forest would make these fluorescent chameleons stand out, and although the researchers did not draw any specific conclusions about what they might mean, they said their "discovery opens up new avenues in the study of the signaling between chameleons and factors of sexual selection that impel the ornamentation ".

In other words, luminescence could be used by individual chameleons to identify other members of their own species, or even possibly even attract potential mating partners.

Titled "Extended bone fluorescence in chameleons", the study appeared in the journal Scientific Reports.

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