While fluorescence has be documented for some time in aquatic vertebrates, parrots are the only tetrapod in which it has been found until very recently. In February of 2017 a team of scientists from Argentina, including Carlos Taboada, Andres E. Brunetti, and Federico N. Pedron, have published in the Proceedings of the National Academy of Sciences their findings of fluorescence in the South American Tree Frog or the Polka Dot Tree Frog (Hypsiboas punctatus) and a new group of fluorescence compounds.
Fluorescence occurs when electromagnetic radiation of a short wavelength is absorbed and then emitted at a longer wavelength in the visible range of light. They took samples of different tissues including skin with absorbed lymph, glandular secretions, lymph from lymph structures, muscle, and connective tissues containing guanine crystals. These samples were tested to determine which contribute to the frogs fluorescence by recording the incident excitation and the resulting fluorescence and recording the fluorescence spectra. It was found that all samples exhibited a maxima that matched the blue fluorescence but only the skin with absorbed lymph exhibited a maxima within the range of green light that is characteristic of this frog. Additionally, because the skin was found to only transmit a very small percentage of light despite appearing translucent and the subcutaneous structures therefore only emitted approximately 1% of observed fluorescence, the skin with absorbed lymph was responsible for the majority of the emitted fluorescence in H. punctatus.
The compound that is responsible for this fluorescence was extracted and purified from lymph and interstitial tissue and it was characterized using a variety of techniques including HPLC-Ion Trap-MS, TOF-MS, MS/MS-based fragmentation, and 1D-2D NMR. HPLC ion trap is used to determine the polarity of molecules in a particular solution; ion trap refers to the use of a electric or magnetic fields to trap charged particles (ions). TOF-MS, or time of flight mass spectroscopy, determines the mass to charge ratio by using an electric field to accelerate the ions. The velocity is characteristic to the particular ratio of mass to charge. 1D and 2D NMR are spectroscopy techniques which determine the molecular structure of an organic compound. They found that the molecule was very polar, evident by its high solubility in water, and that it had a molecular formula of C22H31NO4. They refer to this molecule as Hyloin-L1.
This research is important because it is only the second documented example of fluorescence in tetrapods and the first in amphibians. These frogs are crepuscular and nocturnal so the implication of visual communication via fluorescence would be an interesting subject of further research. Fluorescence in most commonly found in marine organisms and is used as a communication tool and this study brings up a lot of questions about how this translates to terrestrial organisms.
3 comments:
This is a very interesting article! I am also curious about the ecological significance of fluorescence in these organisms. Does the fluorescence increase the risk of becoming prey? Is it used for interspecific communication or mate attraction?
It sure is amazing how complex nature is; we continue to learn new things everyday! I agree with your closing point that it would be interesting to see how florescence affects behavior among the species and with other species.
Very cool! It would be interesting to know about the visual sensitivity of potential predators as well as conspecifics.
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