Wasp predation and wasp-induced hatching of red-eyed treefrog eggs

Eggs often suffer high levels of predation and, compared with older animals , embryos have few options available for antipredator defence. None the les s, hatchlings can escape from many predators to which eggs are vulnerable. I studied early hatching as an antipredator defence of red-eyed treefrog em bryos, Agalychnis callidryas, in response to egg predation by social wasps (Polybia rejecta). Red-eyed treefrogs attach their eggs to vegetation overh anging;water, where they are exposed to arboreal and aerial predators. Wasp s attacked half the egg clutches and killed almost a quarter of the eggs I monitored at a natural breeding site in Panama. Hatching tadpoles fall into the water, where they face aquatic predators. As predicted from improved s urvival of older hatchlings with aquatic predators, most undisturbed eggs h atched relatively late. However, many younger embryos directly attacked by wasps hatched immediately. Embryos attacked by wasps hatched as much as a t hird younger than the peak undisturbed hatching age, and most hatching embr yos escaped. Thus hatching is an effective defence against wasp predation, and plasticity in hatching stage allows embryos to balance risks from stage -specific egg and larval predators. Wasp-induced hatching is behaviourally similar to the snake-induced hatching previously described in A. callidryas , but occurs in fewer eggs at a time, congruent with the scale of the risk. Individual embryos hatch in response to wasps, which take single eggs, whe reas whole clutches hatch in response to snakes, which consume entire clutc hes. Embryos of A. callidryas thus respond appropriately to graded variatio n in mortality risks. (C) 2000 The Association for the Study of Animal Beha viour.