A frog he would a-pooing go

ALTHOUGH Chris Tracy and his team set out to monitor temperature changes in frogs, tracked via implanted radio transmitters, the phenomenon they stumbled on fascinated them even more: the amphibians were excreting the implants through their bladders.

Chris Tracy with one of the frogs that can excrete transmitters.

ALTHOUGH Chris Tracy and his team set out to monitor temperature changes in frogs, tracked via implanted radio transmitters, the phenomenon they stumbled on fascinated them even more: the amphibians were excreting the implants through their bladders.

Tracy, a physiological ecologist at Charles Darwin University's school of environmental and life sciences, had surgically implanted the transmitters into the body cavities of scores of green tree frogs, Dahl's aquatic frogs and giant burrowing frogs, all of whom are close relatives.

"We had a study on temperature in frogs," he says. "We tracked the transmitters, assuming they would be in the frogs, but in some cases they were outside the frogs; that was a bit confusing." This was the case in 75 per cent of the frogs.

It is not unheard of for a transmitter to be found on its own, but usually it would be in the frog carcass or faeces from a predator.

"But in this case the transmitter was just lying on the ground, with no sign of the frog or of a predator."

It was only when Tracy and his team began retrieving transmitters from within other frogs in the study, finding they had somehow travelled to the bladders, that they began to work out what might have been happening. "We thought the reason we were seeing transmitters in bladders in the green tree frogs is they were too big to be excreted in some cases."

Clearly, many other frogs were big enough to pass transmitters through the cloaca, the common opening shared by frog bladders and intestines.

These observations triggered a new study in which they replicated the process by implanting beads in caged frogs. It took up to two weeks for the frogs to excrete the beads.

Then they documented the process in cane toads implanted with beads. "Every couple of days we dissected one of the toads to see where the bead was relative to the bladder, so we could watch the whole process." Within two days the beads were coated with a thin film of tissue, then attached to the bladder. "In the next four weeks the bladder tissue continued to grow and fully envelop it and the bead ended up in the bladder."

Tracy has concluded it is probable all frogs and toads can do this. A subsequent survey of other research revealed fish can also excrete foreign bodies, including fishhooks, and so can some snakes.