Widespread bone-based fluorescence in chameleons

David Prötzel,Frank Glaw,Martina Schwager,Martin Heß,Mark D Scherz,Anouk Van’T Padje

doi:10.1038/s41598-017-19070-7

Abstract

Fluorescence is widespread in marine organisms but uncommon in terrestrial tetrapods. We here show that many chameleon species have bony tubercles protruding from the skull that are visible through their scales, and fluoresce under UV light. Tubercles arising from bones of the skull displace all dermal layers other than a thin, transparent layer of epidermis, creating a ‘window’ onto the bone. In the genus Calumma, the number of these tubercles is sexually dimorphic in most species, suggesting a signalling role, and also strongly reflects species groups, indicating systematic value of these features. Co-option of the known fluorescent properties of bone has never before been shown, yet it is widespread in the chameleons of Madagascar and some African chameleon genera, particularly in those genera living in forested, humid habitats known to have a higher relative component of ambient UV light. The fluorescence emits with a maximum at around 430 nm in blue colour which contrasts well to the green and brown background reflectance of forest habitats. This discovery opens new avenues in the study of signalling among chameleons and sexual selection factors driving ornamentation.

Highlights

Fluorescence has been reported from a wide range of organisms such as plants, invertebrates and mainly marine vertebrate species[1,2,3,4,5,6,7,8,9,10]
Bone has long been known to fluoresce under UV light[20], a phenomenon that has been used in forensic research[21], but no organism has so far been reported to co-opt this phenomenon for fluorescent signalling
We discovered that the crests and tubercles on the heads of many chameleon species emit blue fluorescence when excited with UV light

Summary

Results and Discussion

The thin layer of epidermis acts as an optical filter and shifts the fluorescence towards a ‘bluer’ emission spectrum This externally visible bone-based fluorescence is not restricted to Calumma and occurs in at least 8 of the 12 chameleon genera currently recognized (Fig. 3A). FTs are concentrated around the eye and the temporal region (Supplementary Figs S1–4), which are important areas for colour signalling among chameleons Their distribution differs among species, and even more so among species groups (Fig. 3C). Using UV reflections for communication is apparently more common in closed habitats than in open habitats, as has been shown in chameleons of the genus Bradypodion[30] Members of the latter genus show fluorescence in the head region (Fig. 4F). Fluorescence in terrestrial vertebrates has been underestimated until now, and its role in the evolution of ornamentation remains largely unexplored, but this is a promising avenue for future research

Materials and Methods

Author Contributions

Additional Information