L6 Boswell - Seasonal Breeding

Question 1

Why change the size of your gonads?

Answer 1

• if they are large they sue a lot of energy

- larger gonads are heavier and makes birds easier to target by predators

Question 2

When do the gonads grow?

Answer 2

Birds use photoperiod to predict when their gonads should grow

Question 3

Describe the pathway from the GnRH neurons to the Gonads

Answer 3

1. GnRH is released from the GnRH neurones and transported to the terminal at the median eminence of the anterior pituitary.
2. GnRH diffuses into the AP causing the AP to release gonadotropins LH and FSH into the blood
3. The gonadotropins travel in the blood to the gonads where they stimulate growth, and also the release of the steroid Oestradiol, which has a negative feedback effect on the GnRH neurones, stopping the release once the gonads have grown

Question 4

What is immunocytology?

Answer 4

thinly sliced brain is stained via antibodies:

1. Using antibodies that will bind to the protein you want to see
2. Then use tagged antibodies (such as luminous etc.) that will bond to the first lot of antibodies to make them visualised

Question 5

How are mammals different physiologically in terms of photosensitivity?

Answer 5

The pineal gland produces melatonin in the brain by being stimulated by light.

Both birds and mammals have both the pineal gland and the GnRH neurones, however mammals need both to seasonally breed and birds do not, but have both.

Question 6

Define Photorefractoriness

Answer 6

A physiological state in which an animal is unable to respond to day length that previously induced a change in the activity of the reproductive axis

Question 7

What do long days stimulate?

Answer 7

1. gonadal growth

2. the gradual development of an inhibitory process - that eventually causes the reproductive system to shut down

Question 8

For starlings breeding time coincides with high food availability, what kind of factor is this?

Answer 8

An Ultimate Factor

Question 9

Define:

a) Photostimulated
b) Photorefractory
c) Photosensitive

Answer 9

a) Photostimulated - maximal GnRH synthesis and release (most stained cytochemistry)
b) Photorefractory - minimal GnRH synthesis and release
c) Photosensitive - GnRH synthesis and release is re-started (but not enough for breeding)

Question 10

What is relative Photorefractoriness?

Answer 10

The strength and timing of PR determines the length of the breeding season.

E.g. Quails breed may-august (extended compared to starlings) This is a weaker form of refractoriness; relative Photorefractoriness. The onset is delayed, allowing for a wider ‘window’ of breeding

Question 11

What fine tunes the timing of the window of breeding?

Answer 11

Supplementary cues