The fire salamander, recognizable by its black-and-yellow pattern and toxic skin secretions, has an unexpected ability: it fluoresces under ultraviolet light. New research found that the glow is most visible on the animal’s yellow underside and sides, and that fluorescent compounds released by its skin can remain active for more than 24 hours. The finding adds to scientists’ understanding of a familiar species whose populations are increasingly threatened by habitat destruction and fragmentation and which the International Union for Conservation of Nature (IUCN) has designated as “endangered” on the Red List of Endangered Species.
Fire salamanders typically live in moist forests, streams and mountainous areas. Despite decades of research, scientists are still finding new details about their biology.
Why do fire salamanders glow?
The researchers determined that the fluorescence primarily comes from glands in the salamander’s skin and the substances they release. The secretions can produce bright green and cyan colors when exposed to ultraviolet light.
“It’s interesting that such a well-studied species still harbors such unknown phenomena. It’s a reminder that even the most familiar organisms can harbor secrets that are only revealed when observed using new tools,” said Bernat Briel, a researcher at Barcelona’s Natural Sciences Museum and lead author of the study.
Biofluorescence occurs when a compound absorbs ultraviolet light, which humans cannot see, and re-emits the energy as visible light. It differs from bioluminescence, which is produced through chemical reactions within an organism. Fireflies, for example, generate their own light, while fluorescent organisms must first absorb light from their surroundings.
Scientists once thought biofluorescence occurred almost exclusively in marine organisms, with scorpions considered a rare terrestrial example. More recent studies have identified fluorescent signatures in a growing range of land animals, including reptiles, birds and amphibians.
Researchers have confirmed that fire salamanders fluoresce, but the biological purpose of the ability remains unclear. One possibility is that the glow helps individuals recognize one another or assess potential mates. Another is that it makes the salamanders’ warning colors more visible to predators.
“Fluorescence meets several criteria suggesting a communication function. Fluorescence could help salamanders detect each other in nocturnal or particularly crowded environments, or it could serve as an additional defense signal,” said Martin Kartempos, head of the Insect Symbiosis Division at the Max Planck Institute for Chemical Ecology and co-author of the study.
The discovery that the salamanders’ toxic skin secretions are also fluorescent raises further questions about how they interact with predators and other animals. These proposed functions remain hypothetical, however. Animals with particularly sensitive vision may be able to detect green and cyan fluorescence even when it is very faint, but humans need a UV lamp to observe the effect.
Fire salamanders live in forests where nighttime illumination comes mainly from moonlight and starlight. The researchers note that full moonlight contains more ultraviolet and violet wavelengths than sunlight, whose spectrum is more evenly distributed. Under those conditions, fluorescence could create small green and cyan highlights against the salamander’s yellow markings, potentially making it easier for other salamanders to spot.
Could fluorescence warn predators?
Another possible explanation is aposematism, a defensive strategy in which an animal displays conspicuous colors to signal that it is poisonous or dangerous. Fire salamanders already use their distinctive yellow-and-black markings as warning signals, and fluorescence could provide an additional visual cue.
When scientists identified samandarin more than a century ago, they established a link between the salamander’s warning coloration and its chemical defenses. These highly toxic steroidal alkaloids are produced from cholesterol precursors and contribute to the animals’ chemical protection.
Despite decades of research into salamander toxins and skin chemistry, the newly observed fluorescence came as a surprise.
“Although salamander skin secretions have been studied chemically for decades, we were unaware of any published reports on fluorescence, so the presence of this fluorescent compound was surprising,” says Andres Brunetti, a researcher at the Max Planck Institute for Chemical Ecology and co-lead author of the study.
The chemical substance behind the glow remains unknown
One of the largest unanswered questions is which substances produce the fluorescence. Although researchers have not yet established the chemical identity of the compound, the evidence suggests it may be a previously unrecognized molecule in fire salamanders.
“We do not yet know what the compound responsible for this fluorescence is, but everything points to a previously unknown molecule in this species. Identifying it will be key to understanding its origin and function,” added Salvador Carranza, a researcher at IBE (CSIC-UPF) and another co-author of the study.
The research team is working to identify and chemically characterize the compounds responsible for the effect. Determining which molecules emit light could help explain how the fluorescence is generated and whether it plays a meaningful role in salamander behavior and survival.
What the discovery means for conservation
The findings reveal an unexpected feature of a well-known species and demonstrate how new research techniques can uncover biological properties that have escaped scientific attention for decades.
Determining whether fluorescence affects communication, mating or predator avoidance could also support conservation efforts. Such information may help researchers better understand the behavior and ecological needs of fire salamanders, which already face significant threats from habitat loss and fragmentation.
Scientists from the Institute of Subtropical Biology and the Catalan Herpetological Society also participated in the study. The research forms part of a pioneering amphibian conservation project organized in Catalonia with support from the Barcelona Zoo Foundation.
Source: www.sciencedaily.com
