In Egg, Frog Knows Predators Already

Some say it's never too late to learn new things, but can it be too early?

Apparently not, if the behavior of wood frogs is any indication. Those amphibians can learn to identify predators while still in the egg, according to new research by Alicia Mathis of Missouri State University in Springfield and several colleagues.

After hatching, many amphibians and fish learn to recognize a predator by associating its odor with an alarm pheromone released by injured conspecifics. Mathis' team wondered whether frogs might have that cognitive capacity even earlier, as embryos.

For three hours a day, on six consecutive days, the team exposed wood-frog eggs to water from a bucket containing crushed tadpoles mixed with water from a bucket housing fire-belly newts. (The newts, native to Asia, are unfamiliar to wood frogs, but eat tadpoles of other species.) A control group received newt water alone.

Two weeks after hatching, only the tadpoles that had experienced the combo of crushed-tadpole and newt water reacted when newt water was presented by itself: they stopped moving, a typical anti-predator response.

The study complements previous research showing that frog embryos can learn to distinguish between food flavors even before they hatch. Classes start early in a frog's life, it seems.

The research was detailed in the Proceedings of the Royal Society B.