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Repro Bio 2 > Seasonal Breeding > Flashcards

Seasonal Breeding Flashcards

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Biology 101 flashcards
1
Q

3 types of rhythms

A
  • ultradian (less than a day)
  • circadian (a day)
  • intradian (longer than a day)
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2
Q

Under constant photoperiod conditions, what happens to endogenous circannual oscillation

A

Has a period of about 10 months –> ex) mares under constant long days eventually become anestrus anyway

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3
Q

what is the current proposed theory on how circannual rhythms work

A
  • “cyclical histogenesis” –> cells/tissues have an approximately annual cycle of synchronized regeneration
  • changes in environment are important (photoperiod)
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4
Q

what does the central control point for reproduction lie with

A

altering output of the GnRH pulse generator in the hypothalamus –> changes in brain reflect functional plasticity of neural tissues

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5
Q

what does the reason for having seasonality revolve around

A

giving birth at the time of year most favorable for survival of offspring (spring in temperate climates)

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6
Q

where is seasonality more pronounced

A

the farther a species lives from the equator

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7
Q

do females or males exhibit stricter seasonality in reproductive capabilities

A

females

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8
Q

what are the “ultimate factors” in seasonal reproduction

A
  • food availability (food competition, predator pressure)

- lifespan of individuals (shorter lifespan = more opportunistic)

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9
Q

proximate factors in seasonality

A

-cues animals use to time their seasonality –> photoperiod

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10
Q

what is the predictor option in seasonal breeders

A
  • animals are planners and use a reliable predictor (photoperiod changes) of a future seasonal change
  • conditions may not be optimal when they are fertile, they will be by the end of gestation
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11
Q

what else do species have to take into consideration besides gestation length

A
  • how long it will take them to transition from anestrus to fully functional cyclicity
  • breeding = spring - (gestation + transition)
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12
Q

what is a “critical photoperiod”

A

length of time that melatonin must be elevated each day to achieve the desired effect

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13
Q

what is more important than critical photoperiod

A

photoperiod history –> 8 hours of light, 16 hours of dark to 12 hours of each

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14
Q

what is photorefractory

A

animals kept under stimulatory photoperiods eventually stop responding to them –> reach end of the endogenous circannual rhythm

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15
Q

what is photoinducible

A

after animals become photorefractory, they may need a period of exposure to non-stimulatory photoperiods before they become responsive to stimulatory ones

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16
Q

what does exposure to non-stimulatory photoperiods do

A

hastens the end of the breeding season before the animal would normally cease activity by becoming photorefractory

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17
Q

frequency of GnRH secretion from pulse generator and breeding season association

A
  • high frequency pulses: breeding season (active ovaries from gonadotropin release)
  • low frequency pulses: non-breeding season (little gonadotropin release and inactive ovaries)
18
Q

what is the main direct stimulator of GnRH neurons and what does it do

A

kisspeptin –> GnRH neurons have receptors for kisspeptin and respond to it by releasing GnRH, which disrupts the system that blocks GnRH release

19
Q

GnRH neurons and GnRH secretion in vivo

A

GnRH neurons don’t secrete much GnRH autonomously and don;t organize themselves to do so synchronously (to give pulse release)

20
Q

do GnRH neurons have receptors for gonadal steroids

A

no –> can’t directly respond to feedback from estrogen or progesterone

21
Q

how does cyclical histiogenesis alter hypothalamic drive for GnRH secretion (in general)

A

by altering inputs on the kisspeptin/GnRH system

22
Q

steps in photoperiod control of reproduction (6)

A

1) retina perceives daylight –> endogenous circadian clock via suprachiasmatic nucleus
2) SCN controls melatonin production by pineal gland (only at night)
3) melatonin controls activity of target cells
4) thyrotropes in pars tuberalis of pituitary respond to melatonin and secrete TSH
5) TSH activates hypothalamus to increase DIO2/decrease DIO3 –> T4 converted to T3
6) T3 is main controller

23
Q

long v short melatonin signals

A
  • long = short day

- short = long day

24
Q

what does T3 control in reproduction

A
  • long day breeders: increases in cell types and alterations in connections that increase KNDy neurons –> increased kisspeptin –> increased GnRH –> cycle
  • short day breeders: increase in cell types and connections that inhibit KNDy neurons –> keep GnRH pulse frequency low –> start cycling when they become refractory to input
25
Q

what is the photoreceptor for mammals

A

retina

26
Q

how does retina control melatonin secretion

A
  • nerves project via retinohypothalamic tract to SCN
  • SCN directs fibers to superior cervical ganglion
  • SCG is sole innervation of pineal gland –> secretes melatonin
27
Q

2 mechanisms by which daily photoperiod is transduced through anatomic pathway to control pineal gland melatonin secretion

A
  • oscillating “clock” within neurons of SCN –> circadian rhythms (alter electrical activity of SCN and therefore pineal gland)
  • in the dark, light exposure of sufficient intensity and duration will cause cessation of melatonin secretion
28
Q

what happens if you keep an animal under constant darkness

A

the pineal gland will not secrete melatonin for the whole time –> eventually the circadian pacemaker in the SCN will shut it off due to oscillating activity

29
Q

what happens to the activity of the SCN clock genes under natural conditions

A

entrained to the light-dark cycle –> SCN stimulates pineal gland to secrete melatonin in the dark

30
Q

how does light exposure stop melatonin secretion

A
  • night: adrenergic input onto pineal gland cells from SCG is increased
  • stimulates activity of n-acetyl transferase (rate-limiting enzyme in melatonin synthesis)
  • activity of NAT is 30-70x higher at night –> melatonin synthesis increased
  • at dawn, light exposure on retina causes cessation of adrenergic stimulation –> levels of NAT and therefore melatonin decrease
31
Q

NAT release in ungulates and primates

A

NAT is constantly high –> light exposure functions to breakdown the formed NAT enzyme

32
Q

function of pars tuberalis and melatonin

A
  • pars tuberalis contains cells that produce TSH but don’t have TRH or T3 receptors –> don’t respond to TRH stimulation, not inhibited by T3
  • do have melatonin receptors –> respond to short daily melatonin signals by secreting TSH
  • TSH transported in retrograde manner to hypothalamus
33
Q

thyroid hormone activation locally within hypothalamus

A
  • in hypothalamus, TSH binds to receptors that surround base of 3rd ventricle
  • alters activity of diodinase enzymes that control conversion of inactive T4 to active T3
34
Q

what do the different dioidinases do

A
  • type II diodinase (DIO2) converts inactive T4 to active T3

- type III diodinase (DIO3) catabolizes T4 to rT3 and T3 to T2 (end products inactive)

35
Q

relationship between TSH and DIO2

A

TSH stimulus (long days) causes up-regulation in DIO2

36
Q

2 mechanisms to inhibit frequency of GnRH pulses in ewe non-breeding season

A
  • massively increased sensitivity of the GnRH pulse generator to inhibitory gonadal steroid (estrogen) feedback
  • steroid independent mechanism because a less severe restruction of GnRH pulse frequency is seen in ovarectomized animals
37
Q

mechanism 1 to inhibit GnRH pulses in non-breeding ewe (most common)

A
  • fewer KNDy neurons in ARC, those present have fewer projections to GnRH neurons
  • a subset of dopaminergic (DA) neurons become active –> inhibit GnRH secretion
  • sensory inputs onto DA neurons from glutaminergic neurons are increased (have estrogen receptors)
  • inhibitory inputs onto DA neurons by GABA neurons are inhibited by estrogen
38
Q

mechanism 2 to inhibit GnRH pulses in non-breeding ewe (not as important)

A
  • subset of kisspeptin neyrons are not estrogen sensitive
  • birds: isolate terminals of GnRH neurons so GnRH can’t be released
  • gonadotropin inhibiting hormone
39
Q

while sheep are short-day breeders, their annual cycle is really controlled by long days?

A
  • if you keep them under constant short photoperiods, they will become refractory and stop cycling but won’t start cycling again
  • if you give them long-term constant release melatonin implants, the same thing happens
  • if you keep them under constant long photoperiods, they show robust regular breeding seasons (10 months)
  • need exposure to long days to initiate inhibition
  • short days are not necessary for them to have a breeding season
40
Q

opportunistic breeders

A
  • small, short-lived animals that alter reproductive activity based on food availability (if given enough, they will breed year round)
  • short gestation periods
  • some respond to the promise of food

Repro Bio 2 (9 decks)

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