Scientists discover the first case of fluorescence in frogs

It is not new that some animal species have natural fluorescence. The most well known case is the Green Fluorescent Protein (GFP) purified from a jellyfish and used in laboratories from all the world like a molecular marker.

An interdisciplinary group of Argentine and Brazilian researchers published a study on Proceedings of the National Academy of Sciences (PNAS) in which they present the first case of natural fluorescence in amphibians, specifically in one species of tree frog with wide distribution in South America (Hypsiboas punctatus).

“This find radically modifies what was known on fluoresce in terrestrial environments because it allows us to find new fluorescent components that can have scientific or technological applications and generate new questions on the visual communication of amphibians”, Julián Faivovich, CONICET principal researcher and one the authors of the study, explains.

During the research, the scientists noted that the juvenile and adult species of Hypsiboas punctatus produced the same bright blue green fluorescence on their surface when they were exposed to UV-A /blue light.

Despite the fact that among the vertebrates fluorescence is a phenomenon known in several fish groups, the details of how is that generated have not been identified. In tetrapod vertebrates (that is to say, with four feet), fluorescence is even rarer, and has only been seen in some parrot species and sea turtles.

This is the first case of one amphibian with natural fluorescence, and according to the researchers, this feature would make them increase their brightness and see themselves better during natural light conditions.

“Hypsiboas punctatus is a night species and in natural environments where it lives, the fluorescence contributes in a 18-30 per cent of the total light that comes out of these animals, whereas the remaining percentage corresponds to the reflected light. This is new considering that in terrestrial environment, in general, the influence of fluorescence in collaboration is irrelevant”, describes Carlos Taboada, main author of the study and doctoral student at the Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’(MACN-CONICET) and the Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE, UBA-CONICET).

The researchers learnt that the eyes of the frogs have their maximum sensibility on the area of light spectrum where the fluorescence occurs and they can recognize that fluorescence among them.

“This could help Hypsiboas punctatus individuals to recognize better among themselves during the evening and night. In these areas, these animals increase their brightness when they transform the blue portion of UV of the spectrum, where their visual sensitivity is low, into longer wavelengths, where their sensitivity is greater”, Faivovich describes.

How do they produce this fluorescent emission?

  “This phenomenon occurs due to a combination of the emission of skin and lymph glands that is filtered by the pigment cells of the skin, which are transparent in this species. The origin of the fluorescence is the result of some components called hyloinas”, Faivovich says.

As some particular features of this species are shared with other frog species, the scientists comment that this phenomenon can be extended and indicate that seven families of anura species include some representatives that could be potential candidates. “The fact that they have transparent skins without a great number of color pigments that absorb the visible light produced by the fluorescence can be very important for the existence of this phenomenon”, Taboada adds.

Apart from opening the door to have more research on ecophysiology and visual communication of anura species, this study also promotes the potential biotechnological development from the discovery of the hyloinas.

“The discovery of new fluorescence mollecules is always interesting because the current techniques used in fluorescence are tools applied in different fields of science, such as protein’s biophysics, immunology, fluorescence’s microscopy, DNA detection and sequencing, among others”, Taboada concludes.