Even as little embryos in eggs, red-eyed tree frogs are totally badass. Researchers have discovered that when the embryos are attacked by a hungry predator, they can wiggle their way out of their eggs prematurely, and escape in seconds. This means that even though most of us think of embryos as pretty passive, some are actively fighting for their lives — before they hatch.

S-shaped thrashing movements while releasing enzymes

In general, frog embryos use enzymes released from special "hatching glands" to make a hole in the egg membrane. But red-eyed tree frogs benefit from a design upgrade. By concentrating these cells on the embryo’s body, the embryos avoid leaking out enzymes slowly over a long time period. Instead, the cells store them up and then release them all at once. The embryos also muscle their way out of the membrane by using S-shaped thrashing movements while releasing the enzymes, says Karen Warkentin, a biologist at Boston University and co-author of the study, which was published today in the Journal of Experimental Biology. So instead of taking hours or even up to half the embryonic period to hatch, mature red-eyed tree frog embryos can hatch in seconds — leaving predators with only the slowest of the bunch to munch on.

(Karen Warkentin, Marc Seid)

"For red-eyed tree frogs, their fast-hatching mechanism enables about 80 percent of embryos to escape from snake and wasp attacks, over a pretty broad developmental period," Warketin says.

Generally, these embryos take between six and 50 seconds to hatch, but the researchers found that some can hatch even faster during real attacks. And that’s all thanks to the fast-hatching adaptations that the tree frogs developed. "These might be fairly simple changes, but they make a huge difference in terms of what the embryo can do to defend itself," she says.

There are other frog species that hatch quickly. But this is the first study to actually try and figure out how embryos perform this feat, Warkentin says. So now, the researchers hope to find out if those other species use the same mechanisms. "There is, I think, a huge amount of under-appreciated embryo diversity out there and what embryos can do matters for survival through this earliest –— and often most vulnerable — stage of life."