Premature Ejection

When the going gets tough, some frog embryos get going

• Mark Cheater
• Feb 01, 2001

When the going gets tough, some frog embryos get going. A new study shows that a red-eyed tree frog embryo will hatch early if attacked.

Red-eyed tree frogs are found in tropical rain forests from Mexico to Panama, and females lay masses of gelatinous eggs in plants over water. The eggs usually hatch around seven days later, and the tadpoles drop into the water. Karen Warkentin, a biologist at the University of Kentucky, observed clutches of frog eggs at ponds in Panama and noted the response to predators. When a wasp landed on the clutch and tried to bite open one of the eggs, the embryo frequently popped out and got away from its enemy.

"It's a pretty effective way to escape," says Warkentin, noting that nearly 90 percent of the early-hatching embryos survived the attack.

Not all embryos are capable of such a response, Warkentin notes; they must be at least four days old. Still, the ability of some unborn creatures to sense danger and take action is significant.

"People have not thought about embryos as actively making decisions or responding to their environment," says Warkentin. "This tells us that embryos, at least in some cases, are not as helpless as we thought."