SciShow: Hatching Process in Embryos

Overview

Hatching from an egg is a critical milestone for embryos, marking the transition from a food-rich environment to surviving in the outside world. Scientists have discovered that embryos can sense external conditions to time their hatching appropriately.

Parental Influence

• Some parents, like dancing fiddler crabs, time mating to ensure larvae hatch at times advantageous for survival.

Embryo Autonomy in Hatching

• Streamside salamander embryos can delay hatching if predatory flatworms are detected; this is due to sensing chemicals from predators.
• Red-eyed tree frog embryos hatch early in response to snake attacks or flooding, using different sensory mechanisms like vibrational sensors called neuromasts.

Coordination Among Embryos

• Stinkbug embryos sense vibrations from hatching siblings to hatch simultaneously, avoiding cannibalization by earlier-hatching stinkbugs.

Molecular Mechanisms

• Zebrafish embryos use Thyrotropin-releasing hormone (TRH) to signal hatching, which is produced by the brain and activates the hatching gland to release enzymes dissolving the egg envelope.
• TRH's role is corroborated by studies on medaka fish, suggesting a common mechanism among fish species.

Ongoing Questions

• Understanding how embryos form neural connections to produce TRH.
• Determining the universality of this hatching process across other animals.

Conclusion

Though life within an egg doesn't fully prepare embryos for external challenges, studies reveal various ways they can evaluate and respond to their environments before hatching.