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Flashcards in lecture 8: seasonal breeding Deck (23):
1

What are patterns of breeding cycle?

many patterns:

  • continuous 
  • continuous with seasonal variation 
  • extended period of breeding 
  • very brief breeding season 
  • variation within species depending on environment 

2

Why do we have environmental control of breeding cycles?

  • environmental variation affects survival 
  • powerful selection pressure to time breeding to maximise reproductive success
  • ultimate factors provide the evolutionary selection pressure and include food, temperature, rainfall, humidity 
  • because in many environments the availability of food, temperature etc vary seasonally, and many species breed on an annual cycle cued by photoperiod as a proximate factor 
  • not all species breed seasonally 
    • continuous 
    • opportunistic cued by environmental factors 
  • male – female differences in patterns 

3

What is an example of food as a proximate factor?

  • nutritional influences on reproduction 
    • calorie balance 
    • hormones or other factors in feed 

4

What is an example of hormones and other factors in feed affecting timing of breeding?

  • reproduction response of microtus to wheatgrass supplements 
  • date : treatment : % pregnant
  • 23-25 jan : no grass : 0 
  • 15 - 18 feb: no grass : 0 
  • 15 - 18 feb: grass supplement : 100 
  • 12 - 14 mar : no grass : 5 
  • 10 - 12 april : no grass : 96

5

How can rainfall be used as a cue?

  • correlation among annual pattern of rainfall, number of insects available and percentage of sheath-tailed bats lactating in coastal kenya 

6

What can influence flexibility of breeding patterns?

  • flexibility in breeding patterns depending on location 
  • alternate cues
  • alternate use of cues 
  • rapid selection for variants that maximuse success 

7

What is a photoperiod?

  • correlates with seasonal changes in weather, food etc 
  • most obvious changes in temperate environments 
  • photoperiod changes with latitude 
    • little photoperiod change in equatorial region 
    • extreme photoperiod change in polar regions 
  • absolute daylength vs change in daylength 
  • allows long-term synchronisation e.g. autumn mating for spring births

8

What does photoperiodic control require?

  • photoreceptor (clock) 
  • neural pathway linking clock to neuroendocrine pathways 
  • endocrine response of hypothalamo-pituitary-gonadal axis 

 

  • variation between species 
    • short day breeders
    • long day breeders 

9

Why have seasonal breeding?

  • climate and food availability = survival 
  • ensure offspring born best time 
  • more pronounced away from tropics (greater seasonal variation) 
  • ultimate factors: temperature, rainfall, food availability
  • proximal factors or predictors: daylength 
  • regulating time of conception:
    • short gestation spp: spring e.g. hamster, birds
    • long gestation spp: autumn, e.g. sheep, deer 
    • variable gestation spp (delayed implantation/embryonic diapause) e.g. kangaroo, mustelids, seals 
  • alignment with season crucial for species survival 

10

What is the breeding pattern in Soay sheep?

  • primitive sheep
  • reflect the sorts of breeding in sheep before they became domesticated 
  • become anoestrus following breeding season 
  • very tightly coordinated: march through to may 
  • mortality higher in those born later 
  • very strong selective pressure 

11

What are the circannual rhythms in the Soay ram?

  • high levels of prolactin in winter 
  • FSH levels increasing in advance of rut   
  • sequence of seasonal reactivation similar to puberty 
  • low plasma FSH/LH in spring, LH surg, FSH risin in summer, lower than summer but higher than basal in autumn (pulsatile), testis size increased in autumn, higher pulse rhythm of LH  
  • LH pulses correspond with testosterone, has less frequent pulses than FSH 
  • other circannual rhythms 
    • moulting, antlers, food intake, weight gain, seasonal breeding 

12

What are circadian rhythms in rats?

cyclical activities in the female rat

  • nocturnal activity cycle – a 24 hour cycle 
  • production of oocyte – a 4 - 5 day cycle
    • LH surge (2-4 pm), 5 - 7 h before darkness
    • ovulation (2-4 am), during active period 
  • other circadian rhythms: temperature, melatonin, prolactin, growth hormone, corticosterone, sleep-wake, etc 

13

What is the pineal gland?

  • endocrine gland in roof of brain 
  • photoreceptive in lower vertebrates 
  • receives photic input via suprachiasmatic nucleus and superior cervical ganglion
  • makes the indole hormone melatonin in dark 

14

what is the photo-neuro-endocrine pathway?

seasonality is disturbed by:

  • blinding 
  • lesions of the SCN 
  • ablation of the SCG 
  • pinealectomy

 

  • photoperiod changed and continuous light or dark but usually takes a few days for endogenous rhythm to adjust 
  • long-lasting melatonin implants 

15

What is the control of melatonin secretion?

  • Tryptophan 
    • tryptophan-5-hydroxylase 
  • Serotonin 
    • N-acetyl-transferase (NAT) 
  • N-Acetyl-serotonin 
    • hydroxynindole-o-methyl-transferase (HIOMT)
  • melatonin 

also input on NAT: 

  • nocturnal stimulation 
  • NA - sympathetic nerves 
  • beta receptor 
  • c-AMP 
  • promotes NAT 

16

What are the effects of photoperiod and melatonin on LH in ewes?

17

What were the melatonin profiles in Soay rams moved to continuous dark?

  • endogenous melatonin cycle persists in dark but is normally entrained by light-dark cycle 

18

What is the retino-hypothalamic-pineal tracT?

  • more complicated 
  • where in the system is the endogenous system sat 
  • just remove light: still a 24 hour cycle 
  • take out superchiasmatic nucleus and flat line 
  • SCG - flat line 
  • dark - cycle
  • light - flat line 

19

What is the hormone of darkness?

  • melatonin 
  • melatonin secreted at night 
  • synthesised in the pineal gland and released 
  • reflects the length of the night 
  • changing melatonin profile alters GnRH secretion 

20

What is the distribution of melatonin binding areas?

  • MT receptors in medial basal hypothalamus and pars tuberalis 
  • MT affects electrical activity GnRH neurones 
  • MT affects synthesis of neurotransmitters 

21

What is prolactin secretion and the pelage/moult cycle?

  • seasonal cycle in prolactin secretion in syrian hamster and soay shep 
  • SD = low Prl
  • LD = high Prl 
  • photoinduction = response to change from SD to LD or vice versa 
  • refractoriness = inhibitory or stimulatory effects of photoperiod wear off 

22

What is the biological clock?

  • self sustaining biological clock or oscillator in SCN 
  • constant light or dark free - runs c. 24 h
  • located in suprachiasmatic nucleus 
  • entrained by photic stimuli via retinogypothalamic tract (Feeds photoperiod info to clock in SCN)
  • lesion to tract (SCN to SCG to pineal) disrupts circadian rhythms 
  • rhythm expressed by melatonin secretion 
  • melatonin receptor found in MBH and PT 
  • circannual cycles in prolactin associated with pelage 
  • pars tuberalis has calendar cells 

23

So how do we get control of seasonal breeding?

  • CNS
    • integrates environmental cues like like, olfactory stimuli, temperature...
    • neural signals
  • pineal gland 
    • transducer of photic information from retina 
    • involved in time perception via clock genes 
    • makes melatonin in dark 
    • melatonin 
  • hypothalamus 
    • GnRH release modulated by melatonin (via MBH?) 
    • regulation of steroid feedback 
    • pars tuberalis produces prolactin 
    • GnRH 
  • Anterior pituitary
    • tuberalin from pars tuberalis generate prolactin 
    • GnRH regulates LH and FSH secretion 
    • LH and FSH 
  • Gonads