Theory 76/Timing & Gating/Reproductive biology
Breeding Is Gated by Photoperiod
The claim
The onset of breeding is set by the rate of change of photoperiod rather than by absolute day length, so the same day length signals differently in autumn and spring.
01Mechanism
The reproductive axis responds to the derivative of day length, which distinguishes lengthening from shortening days.
02Prediction
Onset should differ at equal day length by direction of change.
03Refutation
Onset tracking absolute day length would remove the derivative.