Meeting Abstract
Arboreal embryos of phyllomedusid treefrogs hatch prematurely to escape snake predation, cued by low frequency vibrations in their egg clutches. Escape success varies between species, from 80% at 1d premature in Agalychnis callidryas to just 11% in A. spurrelli. However, both species begin responding to snake attacks at the onset of vestibular function. Egg clutches of A. callidryas are thick and gelatinous, while A. spurrelli clutches are thinner and stiffer, affecting whole-clutch and individual-egg movements excited by attacks. Since all vibration cues embryos perceive must propagate through their egg clutches, we hypothesized that differences in the hatching responses to snake attacks in A. callidryas and A. spurrelli are due to the influence of clutch biomechanics on the cues available to embryos. We tested this by embedding egg-sized accelerometers within clutches of both species and performing three standardized excitation tests at varying distances to the accelerometer: pendulum impacts, water droplets, and simulated snake-attacks. Mechanically, thinner egg clutches should have higher resonant frequencies, greater spatial attenuation, and damp more quickly than thicker, more flexible clutches. Initial analyses of clutch free vibrations following impact tests indicate A. spurrelli clutches oscillate at much higher frequencies than those of A. callidryas. A. spurrelli clutches also show greater differences in peak amplitudes between impact distances and faster attenuation of vibrations than A. callidryas clutches. Vibrations induced by water droplets and simulated snake-attacks also appear to differ between species. Vibration biomechanics may constrain the information available to A. spurrelli embryos and contribute to inter-species differences in hatching responses to predator attacks.
