Earlier this month the world learned that the platypus, probably the most unusual mammal, glows greenish-blue under UV light. At first appearing just one more way in which the egg-laying platypus differs from most other mammals, it now looks like shining under a blacklight is actually something the platypus has in common with many fellow Australians. Turns out, lots of marsupials do the same.
After reading the paper in Mammalia reporting on platypus's unexpected nightglow Dr Kenny Travouillon of the Western Australian Museum decided to turn UV light on some other specimens. As curator of mammals, he had plenty of dead mammals in his care and colleagues with the equipment to study animals, such as scorpions, already known to turn short-wavelength radiation into something humans can see.
On the museum's social media sites Travouillon reported his efforts had been rewarded. Not only do echidnas, the platypus's closest surviving relatives, light up under UV, but so do bilbies’ ears, possums, some Australian bats, and the popular favorite, wombats. Others chimed in with their own findings, including reports of glowing Tasmanian sugar gliders and eastern barred bandicoots.
However, the trait is not universal to Australian natives. None of the kangaroo family Travouillon tested showed any color response to UV light, and a variety of other animals were similarly dark.
The tweets led researchers from Curtin University to contact Travouillon about teaming up for a more systematic study. It is hoped this will provide answers as to why some marsupials have this strange trait and others don't.
In the meantime, however, Travouillon told IFLScience his working theories. None of the carnivorous marsupials, including quolls and Tasmanian devils, Travouillon has tried illuminating have shone in response. He thinks this is because such a light show would alert potential prey to their presence, particularly at dusk. Prey might appear to have even more to lose through visibility, but Travouillon noted color-blindness is common among predators, potentially leaving small mammals safe to glow in peace.
“Kangaroos don't need color to see each other because they live in mobs. The solitary animals need to be able to recognize each other in mating season,” Travouillon said. It's not clear how this theory explains the mix among exceptionally sociable bats, however, and Travouillon stresses more thorough testing will be needed before the explanation is much more than a guess.
Travouillon also doubts that platypuses currently use their glow as a mating signal, noting they close their eyes when underwater. Instead, he told IFLScience, it’s probably a legacy left over from some ancient ancestor, like humans' vestigial tailbone.
Some animals that are bioluminescent produce their own light. However, Travouillon sees no sign of this in his specimens, telling IFLScience, they are more likely biofluorescent. “I think their fur just reflects UV light in a particular way, it's probably its chemical composition.”
The fact this widespread marsupial trait has gone unnoticed until now is remarkable because North American opossums have been known to produce psychedelic colors under UV light since as long ago as 1983. Travouillon explained to IFLScience that in a pre-Internet era such findings were easily missed (the opossum paper is still not online), so no one thought to see if the same thing was true in marsupials’ homeland. On the other hand, when the platypus paper came out earlier this month reports shot round the world and Travouillon was examining the specimens he curates in a day.