Scientists say Europe's black-and-yellow fire salamanders show biofluorescence from skin glands and toxic secretions, though the purpose and the responsible compound remain unknown.
Researchers have reported that the fire salamander, one of Europe's most recognisable amphibians, fluoresces green and cyan under ultraviolet light. According to a summary of the study published by ScienceDaily from materials provided by the Max Planck Institute for Chemical Ecology, the glow is strongest on the yellow underside and flanks, and traces mainly to glands in the skin and to the secretions those glands release. Those secretions can keep glowing for more than 24 hours after leaving the animal. The species is listed as vulnerable on the IUCN Red List, and it typically lives in damp forests, streams and mountain areas where habitat loss and fragmentation are growing threats.
The effect is biofluorescence: compounds in the skin absorb ultraviolet light, which humans cannot see, and re-emit it as visible light. It needs an external light source and differs from bioluminescence, in which animals such as fireflies make their own light chemically. Fluorescence was once thought to be found almost only in marine life, with scorpions a notable land exception, but recent work has identified it in reptiles, birds and amphibians. The team, including researchers from the Museum of Natural Sciences in Barcelona, the IBE (CSIC-UPF) and the Max Planck Institute for Chemical Ecology, says it did not know of earlier reports of fluorescence in salamander skin secretions, even though those secretions have been studied chemically for decades.
What the glow is for remains unresolved. The researchers describe two hypotheses that are not yet tested: that it helps salamanders spot one another in dark, dense habitats, where moonlight contains proportionally more ultraviolet and violet light than daylight, or that it adds to the warning signal of their black-and-yellow pattern and toxic alkaloids. The chemical responsible has not been identified, and the scientists believe it may be a molecule not previously known in the species. They are now working to characterise it, which they say could clarify whether fluorescence matters for behaviour or survival and could inform amphibian conservation efforts in Catalonia. The findings come from a single research team's report, and the proposed functions should be treated as open questions.
