Reproduction in Birds- Structure and Function Flashcards
what is so special about birds
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
Gonad Determination
initial embryo development similar to mammals= lead to undifferentiated gonads populated with primordial germ cells
Differentiation of gonads
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
Sex Determination
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
two theories on sex determination
dosage: more Z products without compensation= male
dominance: W powers over Z to become female
birds are more sensitive to estrogens
to feminize –> add estrogen
to masculinize –> add androgens
Ovary
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
Disruption to normal development
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
Gynandromorphic Chickens
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
The Hen: Follicular Development
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
Precursors for yolk formation
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
The Infundibulum
captures the ovum after ovulation
site of fertilization
deposition of the outer vitelline membrane and the chalazae
stay here for about 15 minutes
The Magnum
site of egg white production and deposition
proteins stored in granules in the epithelial cells
3 h transit
The Isthmus
cells in the tubular glands secrete fibrous material
site of shell membrane formation
1.5 h transit
The Shell Gland
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
The Vagina
from the shell gland to the cloaca
muscle layer very well developed
mucosa rudimentary with no tubular glands
contains the sperm storage tubules
Oviposition
increased muscle activity from shell gland
nesting behaviour
coordination with ovulatory cycle
- next ovulation 45 min after oviposition
The Rooster: Sperm Development
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
Fertilization and storage
1 insemination can leaf to over 1 week of fertile eggs
Avian Reproductive Cycle
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
Photorefractoriness
no response to light stimulation: involution of the reproductive tract (no longer an issue in commercial strains of layers)
