Tree frog embryos plop out of their eggs in moments of danger, and now a researcher has found that their responses are proportional to the threat.
That an embryo can respond at all to predators represents a recent rethinking of the powers of eggdom. One of the first pushes for this view came from studies of red-eyed tree frogs (Agalychnis callidryas), which lay their eggs in plants dangling over water. In 1995, Karen Warkentin, now of the University of Kentucky in Lexington, reported that a snake attack can prompt a whole clutch of the embryos to pop out of their eggs early.
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