Meeting Abstract
Many embryos hatch at different developmental stages in response to environmental conditions, using cues in multiple sensory modalities. This is widespread and particularly well studied in amphibians. Phyllomedusid treefrog embryos hatch prematurely in response to hypoxia when flooded and physical disturbance by predators. Recent work on Agalychnis callidryas suggests that hypoxia-cued hatching begins when hatching ability develops, but mechanosensory-cued hatching begins slightly later, once inner ear mechanoreceptors develop. Effective escape-hatching responses to flooding appear ancestral and conserved in phyllomedusids, but responses to snake attacks vary among species. Specifically, the faster-developing species A. spurrelli and A. saltator have lower escape success in snake attacks. We hypothesized that this variation in escape-hatching success might be due to differences in the relative timing of key developmental events. If accelerating development affects hatching mechanisms more than ears, it could increase periods when hatching-competent embryos cannot perceive mechanosensory cues. To test if changing development rate differentially affects the onset of escape-hatching responses to different cues, we reared A. callidryas embryos at cool, ambient, and warm temperatures. Warmed embryos developed faster while cool ones developed much slower. We then assessed the onset of hatching responses to hypoxia and mechanosensory cues. Across thermal treatments, embryos began responding to each cue type at a consistent developmental stage, although the absolute timing of response onset differed. This suggests that developing faster need not always entail a lag in predator-detection ability. Why hatching-competent, but premature, embryos of some Agalychnis species fail to flee from predators remains enigmatic.
