Imagine some buckshot from a shotgun got stuck in your chest or you had a radio transmitter stuck in your side. If you were a frog, your body might be pristine a few weeks afterward — they apparently have the remarkable ability to pee out foreign objects, with their bladders engulfing the intrusions to help get rid of such junk, scientists now find.
No other animal until now has ever been seen using their bladder eliminating foreign objects embedded in their bodies.
Scientists originally implanted temperature-sensitive radio transmitters in three species of tree frogs in Australia to learn more about how temperature-regulating abilities in frogs might vary with the habitats in which they lived. Unexpectedly, after 25 to 193 days, when the investigators recaptured the amphibians to recover the transmitters, many of the devices — up to 75 percent in one species — were no longer in the body. Instead, the implants had somehow migrated to the bladder.
To confirm these bizarre results, the researchers implanted small beads into the body cavities of five Australian green tree frogs (Litoria caerulea) and five cane toads (Rhinella marina). In all five of the cane toads, the beads made it to the bladders, and all five of the Australian green tree frogs expelled the beads within 19 days on average. (The cane toads seemed to have more trouble doing that, with just one peeing out its bead.)
"There was dancing in the lab the first time we had a bead appear after it had been implanted," said researcher Christopher Tracy, a physiological ecologist at Charles Darwin University in Australia.
To see how this strange process might work, the researchers implanted beads in the bodies of another 31 cane toads. Oddly, they found tissue grew from the bladder and surrounded the beads in as few as two days.
"We were truly amazed to see that tissue was growing around implanted beads after only two days, which was even before the surgical scars had completely closed," Tracy recalled.
Next, a thicker and more vascularized tissue with cells resembling those that line the bladder fully enveloped the beads. Once the beads were in the bladders, they apparently floated free in the urine, and got expelled if they happened to drift near the orifice leading out. Bathroom breaks rarely completely emptied frogs' bladders, so beads could remain even after many instances of urination.
Frogs have soft bodies, and they leap about a lot, which could make it easy for sticks, thorns and other foreign objects to pierce their thin skin and enter their bodies. At the same time, frog bladders can hold vast quantities of urine, sometimes even more than the body mass of the frog in some species. As such, their bladders may have naturally evolved to help frogs take out the garbage, a capability researchers suspect many frogs to have.
"This is a pretty amazing way to deal with dangerous objects that might find their way into the body cavity," Tracy told LiveScience. "The simple fact that they these objects can be pushed out of the body safely is quite remarkable."
The researchers now want to understand exactly how the proliferation of tissue occurs around foreign objects and what stimulates these cellular mechanisms. "It seems like there might be some interesting potential along that avenue, in terms of tissue repair and defense mechanisms," Tracy said.
The scientists detailed their findings online Dec. 7 in the journal Biology Letters.