Reproduction in Birds- Structure and Function

Question 1

what is so special about birds

Answer 1

most birds possess 1 functional ovary (left) and one left oviduct

birds lay eggs in clutches= repeat ovulations
- domesticated chickens do not have time between clutches

Question 2

Gonad Determination

Answer 2

initial embryo development similar to mammals= lead to undifferentiated gonads populated with primordial germ cells

Question 3

Differentiation of gonads

Answer 3

starts at embryonic day 6 in chickens (out of 21 days)

testes, medulla, develops with Sertoli cells

ovary, cortex develops with oogonium

both grow at meso-nephrous kidney

Question 4

Sex Determination

Answer 4

Heterologous sex chromosomes carried by females (males ZZ; females ZW)
ZW unrelated to XY as they evolved from different autosomal chromosomes
Z is large and carries the testis determinant factor, DMRT1
the smaller W has few genes and is largely heterochromatic

Question 5

two theories on sex determination

Answer 5

dosage: more Z products without compensation= male
dominance: W powers over Z to become female

Question 6

birds are more sensitive to estrogens

Answer 6

to feminize –> add estrogen

to masculinize –> add androgens

Question 7

Ovary

Answer 7

undifferentiated female gonads produce higher levels of estrogens (from incubation day 5.5)

development of a left ovary, regression of the right

right mullerian duct regresses: left remains and later forms the oviduct

lack of estrogen in males allows testes to develop

Question 8

Disruption to normal development

Answer 8

estrogen may cause
ovotestis formation
exposure of male embryos to estrogenic substances- development of a partial ovary on the left

disruption of estrogenic production in females
- functional testes may appear on the right

Question 9

Gynandromorphic Chickens

Answer 9

Half ZZ and Half ZW
each cell becomes either male or female based on its genetic sex
somatic sex independent of the gonads

male brain is default in chickens

Question 10

The Hen: Follicular Development

Answer 10

at hatch: thousands of prefollicular germ cells are present

5-9 days after hatch: prefollicular germ cells are surrounded by granulosa cells

at sexual maturation, a cohort of small follicles are recruited to develop under FSH

they start producing steroids which stimulate

• calcium deposition in bone
• synthesis of yolk precursors in the liver
• development of the reproductive tract

Question 11

Precursors for yolk formation

Answer 11

transferred tot he follicles

• estrogens stimulate lipid synthesis in the liver up to 14 times= 19g per day
• precursors travel in the form of VLDL to the theca layer
• VLDLs pass through the vitelline membrane, binds to receptor and are internalized by endocytosis
• vitamins also accumulate in the yolk

Question 12

The Infundibulum

Answer 12

captures the ovum after ovulation
site of fertilization
deposition of the outer vitelline membrane and the chalazae
stay here for about 15 minutes

Question 13

The Magnum

Answer 13

site of egg white production and deposition
proteins stored in granules in the epithelial cells
3 h transit

Question 14

The Isthmus

Answer 14

cells in the tubular glands secrete fibrous material
site of shell membrane formation
1.5 h transit

Question 15

The Shell Gland

Answer 15

anterior portion

• water/electrolytes
• initiation of CaCO3 deposition
• 5 h transit

posterior portion (pouch)
- active CaCOe depostion
- protein and enzymes,es help anchoring crystals
total transit 18-22h

Question 16

The Vagina

Answer 16

from the shell gland to the cloaca
muscle layer very well developed
mucosa rudimentary with no tubular glands
contains the sperm storage tubules

Question 17

Oviposition

Answer 17

increased muscle activity from shell gland
nesting behaviour
coordination with ovulatory cycle
- next ovulation 45 min after oviposition

Question 18

The Rooster: Sperm Development

Answer 18

at hatch: thousands spermatogonia are present
after hatch: seminiferous cords and tubes develop

avian sperm have a long tail and a thing head with almost no cytoplasm

testes located within the abdominal cavity= spermatogenesis occurs at core temperature 42ºC

Question 19

Fertilization and storage

Answer 19

1 insemination can leaf to over 1 week of fertile eggs

Question 20

Avian Reproductive Cycle

Answer 20

chick (brooding period) –> >12 h light (up to 20)
juvenile (sexually immature) –> 8h light needed to reset the photosensitive clock

sexual maturation >12h light

active reproductive period 14-16h light

Question 21

Photorefractoriness

Answer 21

no response to light stimulation: involution of the reproductive tract (no longer an issue in commercial strains of layers)