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14. Repro Cycles 2010 - Reproductive Cyclicity Reproductive...

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Reproductive Cyclicity “Reproductive cycles are present so that offspring are presented at a time providing maximal survival”
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Proximate Factors photoperiod ambient temperature (water/air) rainfall nutrition ion concentration in water control adult reproductive activity
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Ultimate Factors lower predation nutrition for offspring those that enhance offspring survival
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Endocrinology of Gonadal Cycles Hypothalamic control via GnRH GnRH released on environmental cues GnRH stimulates release of LH / FSH FSH induces folliculogenesis LH stimulates steroidogenesis
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Photoperiod - Melatonin Photoperiod detected transmitted to the hypothalamus neural signal is transduced into a hormonal response SCN suprachiasmatic nucleus is an integrative center (ie.,neural clock) processes information provided by synchronizing agents (zeitgebers). Hypothalamus
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Pineal Gland Endocrine organ Secretes melatonin Role in ‘clock’ Role in reproduction
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Melatonin Circadian (daily) rhythm of melatonin codes the circannual cycle of seasonal reproduction Melatonin is synthesized by the pineal gland in the darkness exerts an inhibitory action on secretion of gonadotropins long day -> low melatonin -> more GnRH -> reproduction Pinealectomy disrupts the seasonal cadence of reproduction in animals responsive to photoperiod
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Synthesis of Melatonin
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Melatonin and Age
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Age and Melatonin
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Ovarian Activity Can be seasonal or constant Two distinct phases Follicular Luteal Pregnant - normal non pregnant - abnormal
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Mammals
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Estrous Cyclicity ovarian activity in non-pregnant adult mammals associated with distinct period of sexual receptivity known as ESTRUS first half of cycle, - prior to ovulation - known as proestrous diestrous - second phase after ovulation Note: noun = Estrus -- adjective = estrous
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Cycle designation polyestrous - a series of ovarian cycles seasonally polyestrous - 2+ estrous cycles in a breeding season seasonally monoestrous - 1 cycle per season anestrous - reproductively inactive
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Examples of Seasonal cyclicity -Mammals-
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Elephant - polyestrous - 4 cycles - urinary hormones Dehnhard et al. Reproduction 121, 475-484 (2001)
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http://www.izw-berlin.de/en/research/fg4/index.html?reproduktionsmonitoring.html~rechts Panda - monoestrous - cycle Embryonic diapause
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