Seasonal Breeding

Question 1

seasonal breeding

Answer 1

animals mate at certain times of the year (timed HPG axis activation)
timed mating (birth which gives the best chances of survival)
sheep/hamster

Question 2

continuous breeding

Answer 2

all year reproductively active
constant
independent of time of year/environment

Question 3

photoperiod

Answer 3

seasonal changes in physiology (weight,metabolism, fat content, colour, fur)
summer fur=brown winter fur = white
important in industry

Question 4

true seasonality

Answer 4

birth rate switched on/off
(HPG axis on/off)

Question 5

human birth rate and exceptions

Answer 5

human birth rate is constant throughout year, except for
northern finland higher during Jan-May, lower in summer-winter (extreme seasonality)
inuits (northern canada) 1970s-higher birth rates in spring 1980s-moved away from traditional substinence)

Question 6

aim of seasonal breeders

Answer 6

give birth during spring (Mar-Jun)
different animals have different lengths of gestation (horse>mink)

Question 7

seasonal breeders short day

Answer 7

fertile when daylight shortens (autumn) oct-feb
anestrus in spring/summer
sheep/goat/deer/elk
gestational period of 5 months
spring: increased temperature/food (new grass)

Question 8

seasonal breeders long day

Answer 8

fertile when daylight gets longer (spring)
anestrus in autumn/winter
hamster/mice/horse/hare/rabbit
small = breed in spring/early summer, short gestational period (~20days), offspring can be reproductively competent
horse = 11 month gestational period, breed in spring/summer to give birth in spring

Question 9

what does the photoperiod influence

Answer 9

prolactin (skin)
gonads
signals the pineal gland (behind brainstem, contact with 3rd ventricle via pineal recess)

Question 10

neural pathway

Answer 10

light (RHT) signals to SCN (circadian clock)
SCN nerve fibres synapse in PVN
preganglionic fibres run into superior cervical ganglia
pineal gland releases pineal cells (release melatonin and synthesis)

Question 11

melatonin

Answer 11

produced and released by only the pineal gland
increased synthesis and release during night in biological fluids (blood/CSF/urine) short t1/2
daytime has low levels of synthesis and fast breakdown
released from SCN no matter what time of year

Question 12

hamster testes size

Answer 12

remove testes in hamsters = no change to testes size
hamster - testes size changes (large in spring/summerdecrease in winter)

Question 13

3 aspects of melatonin signals

Answer 13

1) duration
2) coincidence hypothesis (sensitivity window to melatonin)
3) amplitude (little change in peak during darkness)

large change in melatonin with photoperiod

Question 14

melatonin release in hamsters

Answer 14

long days causes increased melatonin release = loss of reproductive function (only when administration overlaps with endogenous melatonin)
short melatonin = active reproduction
duration of nightly melatonin in plasma = mediates changing daylength through seasons

Question 15

GnRH

Answer 15

activation by melatonin
GnRH neurons contain melatonin receptors: MT1/2
no evidence of direct effects causing seasonal changes (only on CR)

Question 16

melatonin signalling

Answer 16

kisspeptin neurons contain MT receptors
kisspeptin stimulates GnRH and HPG axis

Question 17

kisspeptin in short and long day breeders

Answer 17

short day breeders (sheep): sheep Kiss-1 mRNA decreased in long days and increases in short days
long day breeders (hamsters): decreases kiss-1 mrna in ARC increased in long days

pinealectomy = stops reduction in kiss-1 and testes weight during short days
kisspeptin administration = stops decrease in testes weight and testosterone during short days

Question 18

GnIH

Answer 18

located in dorsomedial nucleus (DMN) projects to preoptic area (where GnRH neurons located) and form connections
inhibit GnRH/LH release
sheep = high GnIH in long days low GnIH in short days (kisspeptin off GnIh on)
hamster = low GnIH in short days high GnIH in long days (stimulates reproduction/direct response to melatonin)

Question 19

examples of opportunistic breeders

Answer 19

only mate when environmental conditions are suitable (gestation and birth)
e.g. golden spiny mouse/amphibians
breed: 3-4 times a year
gestation: 5-6 weeks
habitat = hot/dry desserts of Egypt (survive with less water)

Question 20

AVP signalling in opportunistic breeders

Answer 20

secreted from posterior pituitary
primary hormone responsible for water retention
increased water permeability of kidney collecting duct = increased water absorption
secreted in reduced plasma volume and increased plasma osmolality (salinity) - when water is scarce

Question 21

female vs male golden spiny mouse

Answer 21

females = smaller ovaries and uterus/failure of follicle development
males = decreased sperm motility/mating/fertilisation

not well understood
amphibian reproduction determined by water availability

Question 22

melatonin in summer/winter

Answer 22

summer = (low) kisspeptin and GnIH stimulated and activates HPG
winter = (high melatonin) inhibits kisspeptin and GnRH

Question 23

day length changes

Answer 23

each daylength occurs twice a year (mar/oct same daylight:darkness ratio) = same nocturnal signal
oct/mar have different environmental period = need to track melatonin duration)
hamsters = increased testes weight during increased daylight (same photoperiod has different effects)