Red-Eyed Treefrog Embryos Pegged as Escape Artists

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The otherwise helpless looking red-eyed treefrog embryos have been pegged as rather expert escape artists with a new study showing that they can hatch up to two days in advance in case of eminent threat.

The study, published in Journal of Experimental Biology, is yet another evidence that indicates that embryos of some species are not passive but rather active and that they interact with their surroundings by not only just receiving information, but also taking action in case there is danger to their life.

If the eggs of the red-eyed treefrog are left undisturbed, tadpoles hatch after a week’s development inside the gooey egg mass and drop into the water below. However, in instances when these eggs are attacked by hungry snakes or wasps or in danger from sudden environmental events like floods or heavy downpours, the developing embryos are able to assess the level of threat and have evolved a quick-release mechanism to escape the egg prematurely.

Smithsonian Tropical Research Institute (STRI), Panama, doctoral student Kristina Cohen led the study wherein scientists studied egg clusters at STRI’s open-air laboratory in Gamboa, Panama. By physically manipulating the embryos to simulate the vibrations caused by predators, they triggered escape responses captured on video.

“They do a shaking behavior while releasing enzymes from glands concentrated on their snouts,” Warkentin said. “That movement seems to push them snout-first against the hole the enzyme makes in the egg membrane. Then they muscle their way out by using big, S-shaped thrashing movements.”

Researchers reported hatching took between six and 50 seconds, with an average of 20 seconds for the premature tadpoles to drop from their perches.

Using scanning electron microscopes, the researchers compared hatching glands of undisturbed embryos within the egg with those of tadpoles immediately after hatching. Undisturbed gland cells contain swollen sacs of hatching enzyme. In the cells of newly hatched tadpoles, these sacs appeared shrunken. The tadpoles use the glands to release a precision-strike squirt of enzyme to make a hole when they are ready to burst for freedom. In contrast, the embryos of other frog species laid in water often have hatching glands more loosely scattered, which release enzymes slowly, over a matter of hours or days.


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