‘Lungless’ frog species actually had little lungs all along

frog small

A frog species once considered unique for its apparent total lack of lungs actually had pipes all along, according to biologists at the University of Florida’s Natural History Museum.

The lungs, described in a study published on Monday in Current Biology, may be simplified and small relative to the species’ roughly 2- to 4-inch frame, but they’re still lungs.

They belong to an endangered species known as Barbourula kalimantanensis, a frog which resides in Indonesian Borneo in chilly, “fast-flowing forested streams” that can range from the upper 50s to lower 60s fahrenheit 

An earlier study, published in 2008, documented apparent lunglessness in the frog species through dissections and microscopes. The study drew comparisons to lunglessness in some salamanders, which take in oxygen in water through their skin (a process known as cutaneous respiration). 

The new study, however, employed a high-resolution CT scanner; the newer tech enabled researchers to identify lungs in two iodine-soaked specimens that had been collected and examined by the previous study’s authors. 

Lead author of the new study, David Blackburn—a professor and curator of the University of Florida’s herpetology collection, described the species’ lungs in an email to Popular Science

If this frog species’ lungs were inflated, they’d be “substantially smaller than your pinky fingernail,” said Blackburn. The lungs of this particular species appear to be far smaller “than the most closely related species that lives on the Philippines island of Palawan,” the biologist added. 

The frog species’ little lungs “suggest a reduced respiratory role,” per the 2024 study. “As such, it may still be the case that cutaneous respiration is important to the physiology of B. kalimantanensis as previously hypothesized.”

Reduced lungs might help some frogs maintain buoyancy in rapid streams; they could also “relate to sound transmission, especially for low frequency calls as have been recorded in B. busuangensis,” the 2024 study also notes. 

The lead author of the 2008 study, David Bickford—a professor of biology and herptologist at the University of La Verne in California, told Popular Science that he “was surprised” by the recent lung discovery. 

“I had thought that we did a thorough job trying to find the lungs,” Bickford said over email. “But with only histology and gross physical dissections at our disposal, we missed them.” The conservation biologist described the shrimp- and larvae-eating frog species as “elusive” and “extremely flattened (probably to reduce drag in fast flowing water).” 

The species is threatened, Bickford added, by habitat loss and pollution linked to logging and gold mining.

“As habitat degradation on Borneo is extensive, the ecology and habitat requirements of the species could become a major liability,” said Bickford. “Any kind of change that alters water quality, especially oxygen content, would seriously affect this frog. We have seen water quality plummet in the areas where we used to be able to find the frogs, and now they are no longer present.”

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