Some are strikingly colorful, but apart from that, many amphibians apparently have other optical features that have so far remained undetected: Under UV or blue light, they shine in green light invisible to our eyes, researchers have found. This ability for so-called biofluorescence appears to be surprisingly widespread in salamanders, newts and frogs. The subtle shimmer could play a previously unknown role in the life of these amphibians, the scientists say.
Many people associate animal glow with the glow worm – but it is an active generation of light through biochemical processes. In contrast to this so-called bioluminescence, biofluorescence is passive: When light from the blue or ultraviolet spectrum hits the surfaces of some living things, special molecules are stimulated to glow. The fluorescent proteins of some cnidarians, which shimmer green or red when illuminated by blue light, are particularly well known. These substances are already used in biological and medical research – for example to mark certain tissues.
Illuminated amphibians
In addition to jellyfish, coral and the like, representatives of many other animal groups have also become known for their ability to perform biofluorescence: fish, insects and even the feathers of some birds fluoresce – for example, for intrinsic communication or for confusing enemies. This remained unnoticed for a long time, since the glow with the naked eye usually remains invisible to humans. As far as the amphibians are concerned, biofluorescence was previously only known from three species of frogs and one salamander. As part of their study, Jennifer Lamb and Matthew Davis from St. Cloud State University in Minnesota have literally shed light on how widespread biofluorescence could be in amphibians.
For their investigations, they shed light from the blue and ultraviolet spectrum on specimens from 32 species of salamanders, newts and frogs. Using spectrometry, they recorded the wavelengths of the light emitted by the animals. The focus was also on a well-known inhabitant of European wetlands and garden ponds: the mountain newt (Ichthyosaura alpestris).
Surprisingly, as the researchers report, they found a basic ability for biofluorescence in all the species examined. Accordingly, blue light most intensively stimulates the animals to shimmer. The emitted radiation lies within the spectrum of green light, the analyzes showed. As the scientists explain, the apparently widespread use of luminosity suggests that biofluorescence is deeply rooted in the development history of amphibians.
What is the shimmer all about?
An interesting range of variation in the patterns and intensities is also evident in the results of her investigation: in some species, the body shines more or less uniformly everywhere, in others, however, spots or stripes were evident. For some, these fluorescent areas correspond to drawings that can also be seen in daylight. In the case of the mountain newt it is shown, for example, that his belly, which is already strikingly orange under “normal” light, is particularly intensively excited to greenish fluorescence in blue light. In some species, however, even bone structures shimmer intensely under the skin, the scientists report.
As they explain, special fluorescent proteins or other molecules in animal tissues could be responsible for the glow effects. Research potential is now emerging in this regard. Because in addition to their biological importance, medical research is also interested in new fluorescent bio-substances, write Lamb and Davis. The question of what significance biofluorescence could have for the amphibians is also exciting. There are already indications that amphibians with certain receptors in their eyes can perceive wavelengths that correspond to fluorescence particularly well. In addition, light signals are important for many species in which blue light predominates – such as at dusk, in shallow water or in the undergrowth.
Under these lighting conditions, the animals could become more visible through the fluorescence – as with other “shining” animal species, there could be meaning in the context of intra-species communication. Alternatively, functions for confusing enemies are also possible. “Our results now provide starting points for future studies to characterize the molecular mechanisms of biofluorescence and their function in the amphibians,” conclude Lamb and Davis.
Source: Scientific Reports, doi: 10.1038 / s41598-020-59528-9