Meeting Abstract
Arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, hatch to escape from egg predators, cued by physical disturbance in attacks. A developmental match in the onset of otic function, measured by the vestibulo-ocular reflex (VOR), and mechanosensory-cued hatching (MCH) suggests that inner ear mechanoreceptors mediate this response. We present three new parts to this story. First, we manipulated development rate by rearing embryos under three thermal conditions (warm, ambient, cool) to assess consistency in the matched onset of VOR and hatching responses to simulated attack cues. Second, we employed confocal microscopy of whole otic capsules of embryos preserved just before and after the onset of MCH (about 3 h apart), visualizing F-actin and synapsin. Initial analyses suggest that VOR and MCH appear concurrently in each thermal treatment. Several morphometrics of inner ears, including abundance and density of stereociliary bundles and their synaptic connections, also appear to increase across hatching onset. Third, we collected a developmental series of high-contrast μCT images of embryo ears to visualize how gross morphology changes across the onset of MCH and through spontaneous hatching. Across the onset of MCH, structural complexity of ears increases, but growth is minimal. After MCH in response to strong cues becomes consistent, ears grow substantially through the rest of the plastic hatching period, while amplitude threshold for MCH in vibration playbacks decreases. Collectively, our morphological data suggest that ear development first enables then improves cue detection. Forming ears, even early in their development, may serve critical functional roles enabling embryos to detect and respond to predator cues.
