ADVANCED LEC 18ORNITHOLOGY

University of Rio GrandeDonald P. Althoff, Ph.D.

ReproductionPart III

Reference Chapters 12 - 17

Now…back to the egg…and more!• Largest egg: ostrich (1,600 g = 3.2 lbs)• Smallest egg: hummingbird (0.3g = 0.009 oz.)• Proportion-wise: emperor

penguin egg is 1.4% of body weight

• Proportion-wise: kiwi egg is 30% of body weight

• Ruddy ducks: largest eggs amongducks: 15% of body wt.

• Mergansers: 10-14 clutch size, each egg 10% of body wt….thus, 100-140% of body wt.per egg-laying period

The Egg…• Supports the embryo from ovum to hatchling• Three major components:

a) yolkb) albumenc) shell

shell

yolk

albumen

Yolk

• Fluid packed with __________• Center of yolk: protein-rich

yolk known as ________ (white in color)

• Latebra surrounded by light & dark layers, which are representative of being laid down by night or day—initial yolk material is laid down months (or years) before laying

Yolk

latebra“white” yolk layer

“yellow” yolk layer

Yolk…con’t

• Rich in proteins & fats• Yolk provides food during a)

development of embryo & b) for newly hatched birds until alimentary (GI) system takes over.

• _______—post hatching iskey to first

_________ survival

Albumen

• Composed almost entirely of ____________ albumen and _____.

• Has thicker and thinner layers:

a) thick, viscous layer drawn out into twisted chalazaeb) chalazae—extend

to ligaments that are attached to the

shell

Albumen…con’t

• Structure and viscosity of albumen serves as ____________________

• Allows embryo to ________ in upper portion of yolk

• Its protein structure __________________ and serves as _____________

• Provides ________________ of nutrition to developing embryo/fetus

ShellComplex membrane consisting of….• Underlying membrane• Testa (main chalky portion)• External cuticle

cuticletesta portion

Inner & outer membranesalbumen

Shell…con’t• Innermost membrane attaches to albumen,

outermost to testa• After laying, ______________________ at blunt

end of egg to form the air space

• Pores in shell are

about 50 um diameter… allowing for _______________

Changes in Weight

• Freshly laid egg has specific gravity _____. Thus, will sink in water

• Older egg (developing or—if infertile and therefore ‘drying out’ vs. ‘developing) will eventually float in water once specific gravity _____. Eggs lose 11-13% of initial weight during first 70-75% of the incubation period.

• Loss of weight due to ___________________

Yolk, Albumen, Shell Components Relative to Developmental Mode

Development Yolk Albumen ShellMode % % %

Altricial 21.8 70.4 7.8

Intermediate 29.9 62.3 7.8

Precoccial 36.6 53.7 9.7

Embryo and Its Development (Chicken egg: 21 days)

• Day 4: head & eyes formed, heart been beating for full day

• Day 9: significant reduction in yolk and albumen

• Day 12: extremities are developing• Day 16: down begins to form• Day 19: feet & toes well developed, all yolk and

albumen used except yolk sac attached to abdomen

• Day 21: chick hatches

refer back to LAB handout with images of developing egg

Hatching

• Just before hatching, __________ is too high for it to lose CO2 through shell pores. Thus, beak thrust into the air space and “air-breathing” starts

• With aid of _____________ (on top of upper mandible), pecking a ____________________ for _______ hours allows for “lid” to pop open.

• Known as “____________”

Hatching…con’t

• Keep in mind, that during the development of the embryo, the shell has continually been ‘weakened’ by the _________________ from it that is subsequently absorbed into the skeleton

• Thus, by the time the pipping process starts, the egg shell is a much easier barrier to break for the soon-to-hatch chick than if it had to the shell at the beginning of the incubation period

Female Reproductive Tract

• ___________ only developed (right side is rudimentary only—most species)

• Eggs produced by ovary are passed into the ___________

• Glands in middle of oviduct produce albumen

• ____________ is near posterior end…lays down the “hard” outer covering

Magnum (first layers ofalbumen added)

Isthmus (inner membrane,outer shell membrane,and albumen added)Uterus with

shell gland

Mature ovum (ready to be ovulated)

Female Reproductive Tract…con’t

• Where shell is added, pigments also added…more _____________________ usually because that is leading end as it move down the oviduct

• ________ critical part of shell contents—responsible for overall structural support

killd

eer

Oyster catcher

DDT…impact on Shell Thickness

• Accumulates usually in predators via __________________ process

• _______ stimulated to secrete certain enzymes to metabolize poisons (i.e., DDT). This also destroys some estrogen which is needed for normal reproduction (both ovum development and “actions” down the oviduct)

• ________ deposit of calcium-rich medullary bone (of female)—source of Ca during egg-laying

Male Reproductive Tract

• See handout (including change in size—E. starling• Testes can increase up to 1,000 fold• Two main cell types:

a) ___________—produce spermb) ___________—assist with

sperm maturation• Testes located ventral side of kidneys (compare to

mammals, which are usually “south” of kidneys)• Sperm carried to cloaca via ductus deferens

Ductus deferens

Testes