Meeting Abstract
Arboreal embryos of Agalychnis callidryas hatch up to 30% prematurely to escape from egg predators, cued by vibrations in attacks. Embryos modulate hatching based on multiple, non-redundant frequency and temporal properties of vibrations, reducing the chance of false alarms that unnecessarily expose hatchlings to increased risk in the water. We used vibration playbacks to test two hypotheses about why hatching responses increase developmentally. First, sensory development might improve cue detection. We constructed amplitude-response curves across stages, using a synthetic stimulus designed to elicit strong hatching responses. We found that the response threshold for hatching decreases substantially with development, consistent with a sensory constraint on cue detection acting soon after the onset of vibration-cued hatching responses. Second, because the cost of false alarms decreases developmentally, but missed cues are still deadly, more developed embryos may accept more false alarms to avoid the risk of sampling ambiguous vibrations. We designed three rhythmic stimuli with predator-like vibration frequencies that varied in duration: interval pattern, and thus information delivery rate. One had a pattern known to elicit high hatching; the others had slower and faster patterns that both elicited little hatching at the first stage tested. As embryos approached spontaneous hatching, their responses to the slow and fast patterns diverged as predicted from their different sampling costs and the changing missed cue–false alarm trade-off. Thus, both developmental constraints on sensory ability and optimal embryo responses to ambiguous information appear to affect developmental changes in embryo behavior at different stages during the plastic hatching period.
