Good vibrations? Sibling embryos expedite hatching in a turtle

A rare and remarkable animal behaviour is communication among embryos within a clutch of eggs. For example, embryonic vocalizations facilitate synchronous hatching in some birds and crocodilians. Synchronous hatching in nonvocalizing turtles suggests a different mechanism of embryonic communication: vibration-induced hatching. We addressed the idea that embryos can communicate with one another via vibrations that expedite hatching in the pig-nosed turtle, Carettochelys insculpta, a species that has evolved rapid hatching in response to hypoxia during nest flooding. Laboratory experiments tested the hypotheses that groups of (sibling) embryos can hatch and emerge more rapidly than solitary embryos, and that a vibration cue can expedite hatching relative to a hypoxic cue alone. We first demonstrated a vibration cue for hatching: vibration-induced hatching latency (ca. 8min) was shorter than the hypoxia-induced hatching latency (ca. 16min). Second, latency to both hatching and emergence from experimental nests was significantly shorter in groups of eggs than solitary eggs, when subjected to hypoxic conditions (perfusion in gaseous nitrogen or immersion in water, respectively). Although we did not directly link vibrations and the sibling effect, leaving open the possibility of embryo vocalizations, our experiments, along with a simple mathematical model, suggest that pig-nosed turtle embryos can detect and respond to sibling vibrations, and that these embryonic signals may increase the survival of siblings by reducing the latency to hatch and emerge under flood conditions. Our results are also novel in revealing multiple hatching cues in a single species within a single environmental context.