Effects of thyroxine on prehatching developmental rate and behavior in the chick

Area of Science:

• Embryology
• Endocrinology
• Developmental Biology

Background:

• Thyroid hormones play a crucial role in embryonic development and hatching timing.
• Previous studies suggested thyroxine accelerates embryonic development.
• Environmental factors, such as egg contact, may influence developmental synchrony.

Purpose of the Study:

• To investigate the effects of thyroxine and thiourea on chick embryo development and hatching.
• To re-evaluate the reported acceleration effect of thyroxine on embryonic development.
• To compare the influence of hormonal treatments with known synchronizing effects of auditory cues (clicks).

Main Methods:

• Chick embryos were injected with thyroxine, the goitrogen thiourea, or saline (control).
• Developmental stages, including beak clapping, clicking, and hatching movements, were recorded.
• Hatching times were compared between treatment groups and control, with and without egg contact.

Main Results:

• Thiourea treatment significantly delayed the onset of beak clapping, clicking, and hatching movements.
• Thyroxine-treated embryos hatched significantly earlier only when incubated in contact with other eggs.
• The observed acceleration by thyroxine in isolation may be an artifact, influenced by synchronizing effects of egg contact.

Conclusions:

• Thiourea inhibits chick embryo development, delaying hatching.
• The previously reported thyroxine-induced acceleration of hatching is likely influenced by egg contact, suggesting a synchronizing rather than a direct acceleration effect.
• Hormonal effects on hatching time should consider environmental factors like physical contact and auditory cues.