1. Photoperiodism in birds
ANSC 332

2. Photoperiod overview Hours of light in 24h period Melatonin
Pineal gland
Breeding

4. In mammals
Optic nerves necessary for regulation of melatonin secretion
If both cut, no change
Constantly high

5. In birds Extra-retinal photoreceptors DBP
Eye receptors not necessary for photoinduced gonadal growth
Pinealectomy
Blinding / sectioning optic nerve
Likely rhodopsin visual pigments
Wavelength of maximum sensitivity = 492 nm
Hypothalamus
Medio-basal

6. Determine # photons of given wavelength reaching base of brain
Standard sensitivity curve
Past trials show red light (650nm)
Passes through brain 30x easier
Skull permeable to light
Sunlight scattered
Stimulate encephalic receptors

7. Circadian clocks 2 clocks SCN (suprachiasmatic nuclei) Pineal Gland
Regulates pineal gland
Present in mammals and birds
Pineal Gland
Present in birds
When isolated, still secretes melatonin rhythmically

8. In summary Mammals Birds Extra-retinal photoreceptors
Brain
Eye pathway not necessary
2 clocks
Optic nerve sends information to pineal gland
Eye pathway necessary
1 clock

10. sources https://link.springer.com/content/pdf/10.1007%2FBF00615153.pdf
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