World-first research by scientists at an Australian university has been unable to solve the mystery of why some rats glow in the dark.
The researchers, from Queensland's James Cook University, used the pelts of 36 dead rats to test if their glow-in-the-dark fur was used for "secret nocturnal communication".
JCU researcher Linda Reinhold said the fur's glow-in-the-dark quality - or photoluminescence - was common, but the reason for it remained unknown.
Ninety-five per cent of mammals from far-north Queensland's wet tropics area display some photoluminescence in the fur, according to the university.
"We wanted to see if predators would be more attracted to either rat, or if the photoluminescence phenomenon was more likely a communication method within similar species," Miss Reinhold said.
"We also wanted to see if it could be a camouflage mechanism.
"Or if rats are sending a warning to predators by standing out, similar to the way some brightly coloured poisonous animals warn of their danger."
To test the theories, the research team applied UV-protectant hairspray to 18 of the dead rats to block the photoluminescence in their fur.
The scientists then fitted the sprayed pelts to "rat-sized models" and left them in three different outdoor environments.
"We deployed pairs of real-fur rat models, one photoluminescent and the other not, and recorded the initial interactions with wildlife on full-moon versus new-moon nights," Miss Reinhold said.
Despite the efforts, the team got no closer to cracking the case.
"We found no evidence for a visual function for blueish-white photoluminescence in the fur of nocturnal mammals," Miss Reinhold said.
"It could be that there is no particular survival advantage or disadvantage for rats and other small land-dwelling mammals of being photoluminescent, at least as an optical signalling function.
"So the mystery continues."
