Developmental changes in red-eyed treefrog embryo behavior increase escape-hatching success in wasp attacks

The arboreal embryos of red-eyed treefrogs (Agalychnis callidryas) hatch prematurely to escape from egg-predators, and escape success increases with age. We assessed developmental changes in the behavior and hatching performance of embryos attacked by wasps (Polybia rejecta) and their contributions to improved embryo survival. We recorded videos of 4- and 5-day-old embryos exposed to wasp attacks and determined each embryo’s fate. For a stratified random sample of embryos that escaped and died, we determined the occurrence, sequence, and timing of events during wasp-embryo interactions. We constructed path diagrams of event sequences, tested for age effects on transition probabilities, and measured durations of periods between key events. Overall escape success was 38% higher in older embryos. They were more likely to hatch pre-emptively than younger ones, thus less likely to experience direct attacks, suggesting that developmental gains in mechanosensory sensitivity may increase hatching responses to indirect cues. During direct attacks, embryos were equally likely to be captured by wasps at both ages and hatching speed was similar, suggesting no relevant difference in escape-hatching performance. After a wasp ruptured their egg capsule, older embryos were more likely to exit and did so much sooner; younger embryos remained in ruptured capsules for longer and were more likely to be attacked again. This developmental change in embryo behavior indicates decreased tolerance for egg-stage risk as the chance of tadpole survival increases, suggesting that ontogenetic adaptation to changing risk trade-offs contributes strongly to the developmental increase in escape success.