Wisconsin scientists discover first Old World animal that shows biofluorescence

Biofluorescence is present in the platypus and several other New World animals. Recently scientists documented it for the first time in an Old World mammal: the springhare.

Biofluorescence is the ability of living organisms to absorb short wavelengths of light and re-emit them at a longer wavelength. The biofluorescence is visible under ultraviolet (UV) light.

The springhare (Pedetes capensis) is native to Africa and, as with other biofluorescent animals, is nocturnal. It looks like a cross between a hare and a kangaroo, but the springhare is not related to either. It is a burrowing rodent, about 14 to 17 inches long, with long hind legs that enable it to move in long, quick jumps up to 6 feet. 

The surprising and serendipitous discovery of vivid springhare biofluorescence is described in detail in an article in Scientific Reports, Feb. 18, 2021. The team of U.S. authors is led by researchers from the Departments of Environmental Sciences and Natural Resources at Northland College in Wisconsin.

Striking visual patterning

The springhare biofluorescence has the unusual "striking visual patterning and intensity of color shift," relative to biofluorescence in other animals, the researchers report. They conclude that the biofluorescence probably comes from the animal's hair fiber cuticle and several "fluorescent porphyrins."

Porphyrins are chemicals involved in making hemoglobin, the molecule that makes blood red. The researchers note that "one unassigned molecule absent from our standard porphyrin mixture" could be involved. 

The authors also suggest that, based on the springhare, biofluorescence "may be ecologically important for nocturnal-crepuscular mammals" and "may be more broadly distributed throughout Mammalia than previously thought."

Orange to red biofluorescence

The researchers examined 14 museum specimens of springhare, which originated in different countries over a period of 58 years, and six captive springhares living in zoos.

The orange to red biofluorescence was more vivid in the living animals than in the museum specimens, but the researchers note that it "was not easily removed via washing." This suggested to them that it was part of the physical anatomy of the springhare hair fibers.

The researchers found that the biofluorescence, which they characterized as "patchy," had the same pattern and intensity in males and females.

A significant finding

Dr. Michaela Rose Carlson, an assistant professor of chemistry at Northland College and a lead author of the article, said that the discovery was significant because "this was the first documented case of biofluorescence in a mammal that originates from Africa, Asia, or Europe."

"Part of what is unique about this biofluorescence," Carlson added, "is that there seems to be patterning on the individuals [that is, different specimens have different fluorescent patterns] which can be seen in the pictures of the live specimens."

"As a chemist, it is also very interesting to me that the chemical compounds [several porphyrins] that are fluorescing are all precursors to the heme found in hemoglobin," she said. "The heme is where the oxygen molecules bind and then the hemoglobin delivers O2 to our muscles and tissues."

As to function, Carlson noted, "At this point we are not sure what the function of this biofluorescence is. We do have a few potential theories though. Many nocturnal mammals are able to see in the UV region. Springhares are also nocturnal, so this biofluorescence could be ecologically significant for the species."

"One potential reason for the biofluorescence could be an indicator of the viability of the specimen as a potential mate," she added. "For example, owls' fluorescence pink and the intensity of their fluorescence can actually signify how old each owl is. It has been proposed that that these owls could be using the intensity of the fluorescence to choose a mate."

Another theory, Carlson said, was proposed by Ana Carolina de Oliviera Neves and Ismael Galván in BioEssays in December 2020. They wrote "that this fluorescence could be how species are filtering out excess porphyrins. In humans, excess porphyrins cause a disease called porphyria which can have some debilitating side effects. Potentially these mammals have evolved to filter the porphyrins out so that they are not incapacitated."

An accidental discovery

Carlson said she joined the team after they had discovered the springhare's biofluorescence, so she wasn't present when it was first found. As she described the discovery, it was a byproduct of the team's other research.

"After finding that New World placental flying squirrels' fluoresce pink, the research team went to the Chicago Field Museum," she said. "The team started opening drawers that were of mammals that would have had a common evolutionary ancestor as the flying squirrels but had evolved separately. One of those mammals was the springhare.

"All of the springhare specimens were vibrantly fluorescent under UV light," she added. "From there the team reached out to zoos that had live springhares to confirm that this was not caused by a preserving technique."

The future

Asked about plans for future research, Carlson said the team is deciding the next directions.

"One direction we are interested in studying is what is causing the purple fluorescence that was seen in the platypus," she said. "This purple color is indicating that UV light is being absorbed. We would like to investigate and see if other species fluoresce purple and then we would investigate why certain species absorb UV light. We also want to investigate other mammals and determine if they biofluoresce, and then if they do, we would like to characterize what chemical compounds are fluorescing."

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E.R. Olson et al., "Vivid biofluorescence discovered in the nocturnal Springhare (Pedetidae)," Scientific Reports, Feb. 18, 2021. DOI: https://doi.org/10.1038/s41598-021-83588-0