Antipredator behavior has been documented in embryos. Work on red-eyed treefrogs (Agalchnis callidryas) and their predators demonstrates how natural selection can produce behaviors on the part of embryos that can, in fact, lessen their risk of predation. Red-eyed treefrogs attach their eggs to the various types of vegetation that hang over water, and once tadpoles hatch, they immediately drop down and take to their aquatic habitat. Both the terrestrial habitat of the egg and the aquatic habitat of the tadpole have a set of dangerous, but different, predators that feed on treefrogs. If terrestrial predation from snakes and wasps is weak, embryos hatch late in the season. Such late hatching allows the frogs to grow to a size that lowers the levels of fish predation, once they hatch and fall into the water.
Both snakes and wasps are terrestrial predators on treefrog eggs, with the latter taking one egg at time, while the former is capable of much more damage per attack. When predation from snakes and wasps is high, it often pays to mature early and drop into the water, away from heavy terrestrial predation. Eggs in clutches that are not disturbed by predators often hatched in about 6 days.
When comparing eggs from these undisturbed clutches to clutches that have already suffered some predation by wasps, hatching rates are dramatically different. Eggs hatched at a much quicker rate when their clutch had been the victim of some wasp predation, with most eggs from attacked clutches hatching in 4 or 5 days (as opposed to 6).
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