Chapter+5+Lectures+B+1+slide+per+page+_Compatibility+Mode_

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SEASONAL REPRODUCTION IN SONGBIRDS
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SEASONAL REPRODUCTION IN SONGBIRDS • Temperate zone songbirds breed on long days • Long days induce reproductive development – Increases in reproductive hormones – Changes in gonad physiology – Changes in behavior (hormone mediated) • Long days also induce eventual termination of reproductive competence
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Long Days Induce Gonadal Growth • Longer days, faster testicular growth in Gambel’s white- crowned sparrows From Farner and Wilson, 1957, Biol. Bull. 113: 257-267.
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Long Days Induce Photorefractoriness • Process that leads to termination of breeding • The longer the days, the sooner the onset of refractoriness in house finches From Hamner, 1966. Gen Comp Endo 7: 224-233.
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HOW DO SONGBIRDS MEASURE DAY LENGTH? • Use “hour glass”? – Directly monitor duration of light period • Use circadian cycle of light sensitivity? – Compare timing of light period with internal clock
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“Resonance experiment” demonstrates circadian cycle of photosensitivity
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House finch
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WHAT IS ONE BIG PROBLEM WITH RESONANCE EXPERIMENTS? • Light signal has two effects: – Stimulates repro system Entrains circadian rhythm of sensitivity
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Light period Rhythm Shift position of light period abruptly, rhythm gradually re- entrains Prolonged resonance photoperiod keeps re-entraining rhythm
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SOLUTION TO THE ENTRAINMENT PROBLEM • Expose to just a single short day • Manipulate when in free-running rhythm short day occurs • Measure something that responds quickly – Hormones, immediate early genes
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Experiment that solves the entrainment problem.
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Effect of photoperiod on intact, pinealectomized and enucleated American tree sparrows From Wilson, 1991. J. Exp. Zool.
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Effect of local cranial illumination on reproductive development From Wilson, 1991. J. Exp. Zool.
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Immediate Early Gene activation after a single long day in Japanese quail From Meddle and Follett, 1997. J. Neuroscience
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Effects of photoperiod on tropical species: Spotted antbird
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Effect of 1 hour increase in photoperiod on gonadal development of spotted antbirds From Hau et al., 1998, Proc Roy Soc
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Effect of 17 minute increase in photoperiod on gonadal development of spotted antbirds From Hau et al., 1998, Proc Roy Soc
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This note was uploaded on 08/02/2011 for the course NPB 102 taught by Professor Hahn during the Summer '09 term at UC Davis.

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