WARKENTIN, K.M.: Hatching as a defense against egg predators: the role of vibrational cues

Red-eyed treefrogs, Agalychnis callidryas, lay their eggs on vegetation overhanging water, into which the tadpoles fall at hatching. The age and developmental stage at which hatching occurs varies. The ability of hatchlings to escape from aquatic predators improves with development, and undisturbed embryos hatch relatively late. However, well before spontaneous hatching occurs, embryos will hatch rapidly in response to attack by egg-eating snakes or wasps. The rapid, synchronous early hatching (escape hatching) appears to be a specific response to mechanical disturbance of the egg clutch by predators. It occurs only after predators have begun physically manipulating eggs, and similar responses can be induced with artificial mechanical stimuli. Embryos are, however, unresponsive to a variety of benign natural disturbances, including wind, rain and earthquakes, as well as to some artificial disturbances. I used a sub-miniature accelerometer inserted among the embryos in A. callidryas egg clutches to record vibrations produced in snake attacks, wasp attacks, rain, and several types of artificial disturbance. I presented these recorded vibrations to hatchable eggs via a minishaker interfaced with the clutches through a set of tines inserted between eggs. Playbacks of recorded snake attacks elicited more hatching than did playbacks of intensity-matched rain recordings. Furthermore, playbacks of natural rain elicited less hatching than did playbacks of rain that were edited to clump drops together and artificially extend still intervals between periods of vibration. Embryos may use simple temporal patterns of vibration to distinguish among benign and dangerous sources of physical disturbance.