Prehatch entrainment of circadian rhythms in the domestic chick using different light regimes

Area of Science:

• Chronobiology
• Developmental Biology
• Animal Behavior

Background:

• Circadian rhythms are fundamental biological processes observed in many animals.
• The prenatal development of these rhythms is crucial for postnatal adaptation.
• The domestic chick serves as a valuable model for studying embryonic development and circadian entrainment.

Purpose of the Study:

• To determine the earliest stage at which circadian rhythms can be entrained in the domestic chick during embryonic development.
• To identify the specific types of light cues (zeitgebers) required for this prenatal entrainment.
• To investigate the developmental timing of brain structures responsible for circadian rhythmicity.

Main Methods:

• Utilized the domestic chick model over four experiments.
• Assessed circadian rhythm presence using tonic immobility (Experiment 1).
• Monitored body temperature to evaluate circadian rhythms (Experiments 1-4).

Main Results:

• Circadian rhythms can be entrained during the late incubation period (prehatch Days 13-18).
• A single day of 12:12 hour light:dark (12L:12D) cues on prehatch Day 13 is sufficient for entrainment.
• Short light bouts, mimicking natural incubation, can entrain rhythms but are less effective than 12L:12D cycles.

Conclusions:

• Prenatal circadian rhythm entrainment occurs earlier than previously hypothesized.
• The maturation of brain structures governing circadian rhythms during embryonic development is more advanced than expected.
• These findings provide critical insights into the early development of biological timing mechanisms.