October 30, 2009

Frog Embryos Learn About Predators By Scent

Frogs can smell predators when they are still embryos, scientists announced recently.

Researchers in the US and Canada discovered that woodfrog embryos could sense any "level of threat" created by salamanders, their enemies.

Embryos placed in water full of the odor of salamanders and the smell of hurt tadpoles memorized the predator's scent as a threat.

Maud Ferarri, biologist from the University of California, Davis, finds that this kind of learning had been tested in fish, amphibians and mosquitoes.

"This, though, is the first time we document that embryos can do it," she said to BBC News.

Ferarri and her team wrote about their research in the journal Behavioral Ecology and Sociobiology.

To create the "chemical cues," the researchers pooled crushed tadpoles with the scent of a salamander.

"We poured these two chemical cues in to the water surrounding the woodfrog egg mass," said Ferrari. "The embryos presumably sample the water and can 'smell' the cues."

Once the embryos grew into tadpoles, the researchers tested their reaction to a salamander.

"A very common anti-predator behavior is freezing," said Ferrari.

"So, to test our tadpoles, we put them in a container with water, and [measured] how much they moved before we introduced the salamander odor and how much they moved [afterwards]."

This indicates that the frogs figured out that the predator was hazardous.

"The results are pretty dramatic," said Ferrari, "tadpoles go from swimming non stop, to not moving at all for several minutes."

The capability to learn at a beginning stage makes sense, Ferrari noted.

"For many species of prey, learning is the only way they have to recognize predators," she said. "Since [this] seems so fundamental to survival... there must be selection for learning to occur as early as possible."


On the Net: