Many animals employ fluorescence: a light show via various biochemical means with a diversity of intentions.
American zoologists Jennifer Lamb & Matthew Davis: “Biofluorescence is the absorption of electromagnetic radiation (light) at one wavelength followed by its reemission at a lower energy and longer wavelength by a living organism.” Several animal phyla employ biofluorescence: cnidarians (e.g., jellyfish), fishes, arthropods (e.g., spiders & insects), reptiles, turtles, birds (e.g., parrots, penguins), rodents, and amphibians.
There are numerous ways to achieve biofluorescence: pigments, mineralization, proteins, and metabolites. Biofluorescence has arisen independently innumerable times. The localized evolutionary force of coherence which guides adaptation typically picks a route of sustainable convenience, following established biomolecular pathways.
“There is striking variation in fluorescent patterning among amphibians, and the primary wavelengths emitted in response to blue excitation light are within the spectrum of green light,” elaborate Lamb & Davis. Some amphibians radiate from their skin. Others have shiny spit or urine. A few have glowing bones.
Beyond aesthetics, which is a showy aspect of Nature, biofluorescence may have various functions: to ward of predators by warning of toxicity, for sexual selection (females preferring a certain glow), as a form of camouflage (hiding from sight with light), and to improve visual acuity (a built-in light).
References:
Jennifer Y. Lamb & Matthew P. Davis, “Salamanders and other amphibians are aglow with biofluorescence,” Scientific Advances (27 February 2020).
Leslie Nemo, “Glow-in-the-dark amphibians are way more common than scientists thought,” Discover (27 February 2020).