BUCKLEY, Christine R.; METCALF, Kelly A.; WARKENTIN, Karen M.; Tulane University; Boston University; Boston University: Egg development affects the foraging strategy of wasps preying on red-eyed tree frog eggs

The red-eyed tree frog Agalychnis callidryas lays its eggs on plants overhanging ponds throughout Central America. Recent studies show that embryos can alter their hatching timing in response to predator and pathogen threats. Eggs typically hatch at 6-7 days of age in Panama, but can hatch as early as 4 days old if disturbed. We found that the Polistine wasp Polybia rejecta typically attacks half the A. callidryas clutches laid at our field site near Gamboa, Panama, posing a significant threat to embryos. Wasps were offered pairwise choices between clutches differing in age by one day (i.e. 0 days/1 day, 1 day/2 days, etc.). We videotaped and scored wasp and embryo behaviors using a computerized event recorder. Wasps spent more time foraging on older clutches within younger clutch pairs (up to 2 days/3days), but showed no preference for older or younger eggs among older pairs (3 days/4days and 4 days/5 days). Wasps also exhibited increased success on older clutches (3-5 days), regardless of pair type. Embryos of intermediate age suffered the highest mortality, and older eggs had the highest rate of escape by hatching. Critical to egg defense is the thick jelly coating provided by the mother at oviposition, which covers the egg mass and gets thinner as eggs develop. While older eggs are more likely to escape by hatching, younger eggs are difficult to for wasps to extract through their jelly layer, resulting in maximal wasp success on intermediate clutch ages (3 days). In addition to providing a physical barrier, this jelly coating may shift predation pressure to older eggs, increasing the embryo�s chance of survival via escape hatching.