Hitting the Ground Running: Environmentally Cued Hatching in a Lizard

Evidence is accumulating for the ability of animal embryos to hatch early in response to the immediate threat of egg predation. However, early hatching in response to predation is known from only amphibians, fish, and invertebrates. Herein we present the first quantitative evidence for induced early hatching in a reptile. In two laboratory experiments, delicate skink (Lampropholis delicata) embryos responded to a surrogate predator cue—vibrations—by hatching ∼3 days earlier than their spontaneously hatching clutchmates. Early hatching embryos were significantly smaller and left more residual yolk in their eggs, however, suggesting a cost to hatching early. Assuming our vibrations were interpreted as an increase in predation risk, skink embryos can thus forego some yolk absorption and growth when threatened by imminent predation. Simulated predation experiments in the field induced hatching in both nest sites (horizontal rock crevices) and in eggs displaced from nest sites. The hatching process was explosive: early hatching embryos hatched in seconds and sprinted from the egg an average of ∼40 cm as they hatched. Our results are unusual in demonstrating early hatching in a terrestrial animal with a simple life cycle, and likely extend predation-induced early hatching to reptiles. Early hatching may be widespread in oviparous vertebrates.