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Flashcards in Seasonal Breeding Deck (29):
1

Ultradian rhythm

those that occur at intervals of less than a day

(heartbeat, respiration)

2

Circadian rhythm

those that occur around a day in length

(body temperature, adrenal activity, sleep/wake cycles)

3

Intradian rhythm

those that occur at periods of longer than a day

(estrous cycles, migration, pelage changes, hibernation, seasonal reproduction)

4

Circannual rhythm

those with an annual occurrence

5

Cyclical histogenesis or histogenesis hypothesis

-cells/tissues have an approximately annual cycle of synchronized regeneration (growth, remodeling, degeneration, and replacement)
-changes in the local environment of the stem cells are considered vital for generation of these circannual rhythms

6

Why develop a seasonal reproduction?

to give birth at the time of year most favorable for the survival of offspring

7

Explain change in seasonality and closeness to the equator

species living on the equator may breed continuously while those at higher latitudes will exhibit strict seasonality

8

Explain change in seasonality between males and females

-females usually exhibit stricter seasonality in their reproductive capacities than males
-males of most species can often breed year round

9

Name some ultimate factors in seasonality (7)

food availability
expected milder environmental temperatures in certain seasons
food competition
predator pressure
lifespan of individuals
foraging strategy

10

Name some proximate factors in seasonality (1)

photoperiod (light = photophase, dark = scotophase)

11

What is the predictor option?

planner species that use a reliable predictor of a future seasonal change as a timing device for maximal reproductive competence

12

What must a species take into account when considering triggering reproductive competence?

gestation length
how long it will take them to transition from anestrus to fully functional cyclicity

13

Critical photoperiod

length of time that melatonin must be elevated each day to achieve the desired effect (melatonin elevated at night)

14

Photoperiod history

animal detects changes in day length based on light exposure (8L:16D to 12L:12D = increase in day length)

15

Photorefractory

when an animal is kept under stimulatory photoperiods and they eventually stop responding to them

16

Photoinducible

animals that need exposure to non-stimulatory photoperiods before they become responsive to stimulatory ones

17

What is the critical event for breeding season vs. non-breeding season?

alteration in the frequency of GnRH secretion from the pulse generator

18

Describe GnRH secretion in the breeding season vs. non-breeding season of females

Breeding season - high frequency GnRH secretion gives gonadotropin release and active ovaries

Non-breeding season - little synthesis or secretion of GnRH and ovaries are inactive

19

What stimulates GnRH neurones?

a peptide called kisspeptin

20

Steps in photoperiod control of reproduction

1. ambient daylength perceived by retina, entrains endogenous circadian clock in SCN
2. SCN controls melatonin production by pineal gland (occurs at night)
3. circulating melatonin levels control activity of target cells
4. thyrotropes of pituitary respond to short melatonin signals (long days) by secreting TSH
5. TSH activates cells in hypothalamus to convert T4 to T3
6. T3 controls tissue histogenesis causing increased GnRH circulation in long-day breeders and decreased GnRH circulation in short-day breeders

21

Explain the steps in measuring day length

retina projects to suprachiasmatic nucleus (SCN) - SCN projects to superior cervical ganglion (SCG) - SCG innervates pineal gland - pineal gland secretes melatonin

22

What can stop melatonin secretion?

during hours of darkness, light exposure of sufficient intensity and duration will cause the cessation of melatonin secretion

23

How does light exposure stop melatonin secretion?

light exposure on retina causes cessation of adrenergic stimulation on N-acetyl transferase, the rate-limiting enzyme in melatonin synthesis

24

How do melatonin signals act on the pituitary gland to cause TSH release?

thyrotrophys of the pars tuberalis have melatonin receptors - melatonin receptors release TSH in response to short daily melatonin signals

25

How does TSH act within the hypothalamus?

TSH binds to receptors in hypothalamus - hypothalamus converts T4 to T3 - T3 important in histogenesis

26

How is the frequency of GnRH pulses inhibited during the non-breeding season? (ewe is example)

-increased sensitivity of the GnRH pulse generator to inhibitory gonadal steroid (estrogen) feedback
-also a steroid independent mechanism at work

27

Explain the inhibition of GnRH using mechanism 1 (altered sensitivity to steroid feedback)

-GnRH stimulatory kisspeptin system is down-regulated by estrogen feedback
-GnRH inhibitory dopamine system up-regulated by estrogen-sensitive glutaminergic and GABAergic inputs to it

28

Explain the inhibition of GnRH using mechanism 2 (steroid-independent inhibition of GnRH release)

-isolation of GnRH neurons from capillaries
-Gonadotropin Inhibiting Hormone (GnIH)

29

What are opportunistic breeders?

small, short-lived animals that alter their reproductive activity based on food availability

(have short gestation periods)