Intense bone fluorescence reveals hidden patterns in pumpkin toadlets

Sandra Goutte,Stéphane Pallu,Didier Merle,Hugues Portier,Lilian Cazes,Mathieu Thoury,Marta M Antoniazzi,Luís Felipe Toledo,Stefan Schramm,Matthew J Mason,Hanane El-Hafci,Pierre Gueriau,Carlos Jared

doi:10.1038/s41598-019-41959-8

Abstract

The phenomenon of fluorescence can be used by animals to change effective colouration or patterning, potentially to serve functions including intra- and interspecific signalling. Initially believed to be restricted to marine animals, fluorescent colours are now being described in an increasing number of terrestrial species. Here, we describe unique, highly fluorescent patterns in two species of pumpkin toadlets (Brachycephalus ephippium and B. pitanga). We establish that the origin of the fluorescence lies in the dermal bone of the head and back, visible through a particularly thin skin. By comparing them to those of the closely related species Ischnocnema parva, we demonstrate that pumpkin toadlets’ bones are exceptionally fluorescent. We characterize the luminescence properties of the toadlets’ bones and discuss the potential function of fluorescent patterns in natural lighting conditions.

Highlights

Luminescence induced by absorption of photons, i.e. photoluminescence, is the process by which an electron from an atom, molecule, or crystal in an excited state undergoes a transition to a lower energy state, e.g. the ground state, and in doing so, emits a photon
We describe fluorescent patterns created by ossified tissues, visible through the skin of two species of pumpkin toadlets (Brachycephalus ephippium and B. pitanga; Brachycephalidae)
We characterize these fluorescent structures using a combination of histological fluorescence and X-ray imaging techniques, compare them with those of close relatives of similar size, Brachycephalus hermogenesi and Ischnocnema parva, and discuss their potential functions

Summary

Introduction

Luminescence induced by absorption of photons, i.e. photoluminescence, is the process by which an electron from an atom, molecule, or crystal in an excited state undergoes a transition to a lower energy state, e.g. the ground state, and in doing so, emits a photon. Fluorescence has recently been described in birds[1], spiders[2], frogs[3] and chameleons[4]. We describe fluorescent patterns created by ossified tissues, visible through the skin of two species of pumpkin toadlets (Brachycephalus ephippium and B. pitanga; Brachycephalidae). We characterize these fluorescent structures using a combination of histological fluorescence and X-ray imaging techniques, compare them with those of close relatives of similar size, Brachycephalus hermogenesi and Ischnocnema parva, and discuss their potential functions

Methods

Results

Conclusion