The fourth experimental series tested whether embryos removed from the female could entrain to a new light-dark cycle.
This finding prompted the question: How does the female entrain the rhythm in the embryos?
Eye pigment development was evident in embryos about 4-5 days before egg hatching, which suggests that young embryos could not perceive and entrain to the light-dark cycle with their eyes.
In contrast, eggs removed from females before exposure to the "delayed" light-dark cycle did not entrain to the new cycle (Fig.
The third experiment tested whether detached embryos could entrain to a new light-dark cycle independent of the female.
Collectively, the results support the model that females detect environmental cycles and entrain the endogenous rhythms in the embryos.
Alternatively, eggs removed from females before exposure to the delayed light/dark cycle did not entrain to the new cycle.
The mean times of hatching and larval release clearly indicate that eggs removed before entrainment to the de-layed light/dark cycle did not entrain, whereas eggs that remained attached to the female did entrain.
To validate this model (1) the eyes in mature embryos must have functional photoreceptors that can perceive the light/dark cycle, and (2) embryos must be able to entrain to the light/dark cycle without input from the ovigerous female.
However, females that had both eyes removed did not entrain to the new light/dark cycle and released larvae (mean times = 2105 to 2132 h for the three bouts of release) near the time for the beginning of the dark phase (2000 h) in the light/dark cycle before entrainment.
In contrast, the eggs that remained attached to the female and were removed from her on the day of larval release did entrain to the delayed light/dark cycle.