Tricks of nature, with and without light

The fur of Australia’s unique platypus glows green under ultraviolet light, while at least two species of the country’s bees have adapted their vision for night conditions.

These two quirks of nature have been revealed by research teams on opposite sides of the world.

The first comes from the US, where researchers had previously discovered, as reported in Cosmos, that flying squirrels have fur that biofluoresces under UV light. The opossum does too, and now the platypus (Ornithorhynchus anatinus) can be added to the list.

It is the first observation of biofluorescence in an egg-laying mammal (monotreme), suggesting, the researchers say, that this trait may not be as rare as previously thought.

The discovery – reported in the journal Mammalia – was led by Northland College, and came about rather by accident.

While confirming field observations of flying squirrels with preserved museum specimens, the team decided to examine the platypuses held by the Field Museum of Natural History in Chicago and the University of Nebraska State Museum.

In visible light, the fur of all three specimens was uniformly brown, but under UV light they appeared green or cyan. The fur of the platypus absorbs UV (wavelengths of 200-400 nanometres) and re-emits visible light (500-600 nanometres), making it fluoresce.

Lead author Paula Spaeth Anich says she and her colleagues are interested in seeing how deep in the mammalian tree the trait of biofluorescent fur goes.

“It’s thought that monotremes branched off the marsupial-placental lineage more than 150 million years ago,” she says, “so it was intriguing to see that animals that were such distant relatives also had biofluorescent fur.”

The second study was homegrown. Researchers from Adelaide’s three universities and the South Australian Museum observed night-time foraging behaviour by a nomiine (Reepenia bituberculata) and masked (Meroglossa gemmata) bee species.

They say the bees have developed enlarged compound and simple eyes that allow more light to be gathered when compared to their daytime kin.

Both species are mostly found in Australia’s tropical north, but there could potentially more in arid, subtropical and maybe even temperate conditions, according to James Dorey from Flinders University, lead author of a paper in the Journal of Hymenoptera Research.

“It’s true that bees aren’t generally known to be very capable when it comes to using their eyes at night, but it turns out that low-light foraging is more common than currently thought,” he says.

“Before this study, the only way to show that a bee had adapted to low-light was by using difficult-to-obtain behavioural observations, but we have found that you should be able to figure this out by using high-quality images of a specific bee.”

Dorey says bees that forage during dim-light conditions aren’t studied enough, with no previously reliable published records for any Australian species.

“Our study provides a framework to help identify low-light-adapted bees and the data that is needed to determine the behavioural traits of other species.”