Frogs debug themselves by absorbing tracking devices into their bladders

By Ed Yong | December 7, 2010 7:00 pm


Christopher Tracy found the three radio transmitters lying on the forest floor. They were still intact and sending off a strong signal, but there was a big problem – all three of them were meant to be inside the body of a frog.

Several weeks before, Tracy had implanted transmitters into three species of Australian frogs to track their whereabouts. He had placed the devices into the frogs’ peritoneal cavity, a space within its belly that contains its stomach, guts and liver. But these ones were alone, with no bodies nearby or any signs of predators. The frogs hadn’t died or been eaten, but they had somehow removed the transmitters from an enclosed space within their bodies.

When Tracy located his other tagged frogs, he found an important clue: around three-quarters of the transmitters had moved to the animals’ bladders. Tracy was intrigued. He rounded up five more Australian tree frogs and five cane toads, implanted small beads into their bodies, and tracked them solidly for two to three weeks. After that time, he found that four of the toads had the beads in their bladders, and the other animals had urinated theirs out.

Bead_diagramTo track the beads’ expulsion more carefully, Tracy captured another 31 cane toads, stuck more beads into them and dissected them on successive days. He found that a thin flap of tissue slowly grew from the bladder and soon enveloped the beads, in as few as two days for some animals. Once surrounded, the beads were covered by another thicker layer, full of blood vessels. Soon, they were pulled into the bladder itself, floating freely until they happened to be peed out.

Many animals have managed to expel transmitters and other foreign objects from their bodies, including fish, snakes and crocodiles. Even in humans, surgical sponges left in the body have sometimes wormed their way into the intestines, only to be removed through the usual route. But all of these species purge their internal rubbish through the intestine or the skin – the bladder is a new route, although perhaps not an unexpected one.

Frogs famously jump a lot, and risk getting punctured by sharp nearby objects; the insects they swallow whole can also come in spiny shells. It makes sense for them to be able to get rid of any unwanted bodily junk. The bladder presents a good route – frog bladders are very large and they take up a lot of room. Any intruding objects are more likely to come into contact with the bladder than any other organ.

It’s a cute result, but one with potential importance for scientists who track amphibians – it could lead to people drawing false conclusions about the death or disappearance of frogs that had simply managed to debug their bodies.

Reference: Biology Letters

Photos by Michael Linnenbach and LiquidGhoul

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Comments (9)

  1. Aaron

    The CIA was pissed . . .

  2. Walter S. Andriuzzi

    I wonder what erpetologists will come up with now to track these wee-powerful frogs. Larger transmitters? They could hamper the animal and reduce its survival potential. Inserting them in other body cavities? If even the peritoneum wasn’t safe. Perhaps something on the skin? I see problems with that too. Mmm…

  3. Aurora

    I had the same thought as Walter S. Andriuzzi: I wonder how herpetologists will adapt to this new info… But you have to love the way Nature beats us at every turn!

  4. Daniel J. Andrews

    We had a similar problem with our fish (northern pike, lake trout) ejecting their internal transmitters through the skin back in the early 90s. That was the first I’d heard about that at the time so was pretty “wow’d”. Through the bladder is even cleverer though.

    Good thing humans aren’t as adept at this–you don’t want to be passing pacemakers and artificial knees through the same route as the frog (or a fish, for that matter). Ow.

  5. Brian Too

    @4. Daniel J. Andrews,

    Yeah, I understand that passing a kidney stone can be painful. What’s it like for a frog to pass a tracking transmitter? Sounds like an owie.

  6. Swift Loris

    How big are the transmitters?

  7. I once had a Japanese quail expel a (large!) radiotransmitter by embedding it into an egg shell and laying it! Nobody, not even my PI, believed me! Now I feel vindicated – these kinds of things are possible, at least in some species…

  8. Frogs only have one hole, though: everything exits via the cloaca. In humans we have the expandable anus option or squeezing stuff out of the urethra – an evolutionary restriction that means pain in the japseye when excreting kidney stones, so I’m told.

  9. blah

    Even the frogs are smart enough to not let anyone track them. Only humans are that stupid.


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