In the Atlantic Forest in Eastern Brazil, the pumpkin toadlets use their bright colours to warn the other species which can attack them. But scientists have also discovered that these frogs display a signal which is otherwise unknown. Under ultraviolet light, they glow as bright blue. The findings were published in Scientific Reports.
The pumpkin toadlets reside in moist tropical and subtropical forests. As their ears are not developed properly, these frogs are deaf to the mating calls of their own species. Currently, they are the only known species that are deaf to mating calls. While investigating this, scientists accidentally discovered the glowing patterns in two species, Brachycephalus ephippium and Brachycephalus pitanga.
When observed under natural light, they appear as orange, red or yellow. But when put under UV light, several blue patterns came up on head, back and legs of the toadlets. This is known as fluorescence and it is very rare in vertebrate animals which reside on the land. Scientists are still not sure how fluorescence helps these frogs. It may help them in identifying attackers from beforehand, take preventive actions or identify prospective partners for reproduction.
Fluorescence differs from bioluminescence, in which the body of the animals produces light with the help of chemical reactions. But fluorescence will not function in total darkness as in fluorescence, light is absorbed by some specific molecules and then it is emitted at larger wavelengths, such as red or green which finally creates a glow.
Animals which display fluorescence are corals, scorpions and sea turtle. Scientists also discovered in 2018, that chameleons also show fluorescence. Besides this, another team of researchers found out that two species of a tree frog found in South America have fluorescent skin. But in case of the frogs, the glow originates from the bones similar to that of chameleons.
Researchers observed through chemical analysis that the bony plates which were located on the head and back of the toadlets were very fluorescent. The cells which exhibit fluorescence are also called fluorescent chromatophores. They contain pigments called fluorosomes which contain proteins that are activated with the help of potassium ions. The fluorescent patterns arise from the motion and aggregation of these pigments within the chromatophore.
It is still not known clearly how do the toads use fluorescence for their benefit. It may serve as a warning sign to animals about the toxic nature of the skin as some birds can detect fluorescence in natural light. It can also be used for communication among themselves, as the toads lack the middle ear so they cannot hear calls from their own species.