lecture 8: seasonal breeding Flashcards
1
Q
What are patterns of breeding cycle?
A
many patterns:
- continuous
- continuous with seasonal variation
- extended period of breeding
- very brief breeding season
- variation within species depending on environment
2
Q
Why do we have environmental control of breeding cycles?
A
- 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
Q
What is an example of food as a proximate factor?
A
- nutritional influences on reproduction
- calorie balance
- hormones or other factors in feed
4
Q
What is an example of hormones and other factors in feed affecting timing of breeding?
A
- 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
Q
How can rainfall be used as a cue?
A
- correlation among annual pattern of rainfall, number of insects available and percentage of sheath-tailed bats lactating in coastal kenya
6
Q
What can influence flexibility of breeding patterns?
A
- flexibility in breeding patterns depending on location
- alternate cues
- alternate use of cues
- rapid selection for variants that maximuse success
7
Q
What is a photoperiod?
A
- 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
Q
What does photoperiodic control require?
A
- 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
Q
Why have seasonal breeding?
A
- 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
Q
What is the breeding pattern in Soay sheep?
A
- 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
Q
What are the circannual rhythms in the Soay ram?
A
- 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
Q
What are circadian rhythms in rats?
A
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
Q
What is the pineal gland?
A
- 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
Q
what is the photo-neuro-endocrine pathway?
A
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
Q
What is the control of melatonin secretion?
A
- 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
Q
What are the effects of photoperiod and melatonin on LH in ewes?
A
17
Q
What were the melatonin profiles in Soay rams moved to continuous dark?
A
- endogenous melatonin cycle persists in dark but is normally entrained by light-dark cycle
18
Q
What is the retino-hypothalamic-pineal tracT?
A
- 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
Q
What is the hormone of darkness?
A
- 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
Q
What is the distribution of melatonin binding areas?
A
- MT receptors in medial basal hypothalamus and pars tuberalis
- MT affects electrical activity GnRH neurones
- MT affects synthesis of neurotransmitters
21
Q
What is prolactin secretion and the pelage/moult cycle?
A
- 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
