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Chapter 15 in Gill. I.
Sexual
reproduction
In breeding season, birds
compete with each other for the chance to breed
mates
resources
balance between cooperation
and competition determine breeding system
monogamous
polygamous
polyandry
polygynous
helpers at the nest
territorial
colonial
clutch size
altricial vs. precocial
Well get to this but first the nitty gritty
Gonads
paired testes
single (usually) ovary
[overhead]
exceptions are
Brown Kiwis
many raptors
some pigeons, gulls and
passerines
testes expand 4-500 xs in mass, nonbreeding season usually a couple of
mm.
Ovary looks like cluslter
of grapes
500- several thousand
primary oocytes
Hormones
Follicle-stimulating
hormone regulates gamete production in both sexes
Luteinizing hormone (from
Pituitary)
controls breeding
physiology in both sexes
regulates hormone
production in testes
stimulates maturation of
ova
controls some secondary
characteristics
Testes and ovary produce estrogen and testosterone, which are both
present in both sexes. Different
ratios and effects.
Secondary characteristics
mostly controlled by
estrogen/testosterone ratios
male breeding plumage
bill color
wattles
Sex determination
females heterogametic
ZW = female
ZZ = male
gynandromorphs II.
Sperm
production
Testes
Produce sperm
secrete hormones (notably
testosterone)
internal - implications?
sperm produced at night
stored in seminal vesicles
in cloacal protruberence
sperm mostly typical of
vertebrates - 3 parts
head - acrosome and nucleus
- the payload
midpiece
- fuel
axial
filament & tail
oscine passerines have spiral head and helical tail membrane III.
Maturation
of the ovum/embryo
parts of the egg
ovum/embryo
food supply
protective layers
yolk added to ovum
in follicle
in layers - most in week
before ovulation
prior to ovulation
follicle ruptures
ovum released into
infandibulum/ostium - funnel end of oviduct
now ready for... IV.
Fertilization
Copulation via cloacal
kiss
some birds have penis-like
structure
most waterfowl (copulation
in water?)
seems taxonomically
haphazard - 1 passerine
female overts cloaca,
exposing end of oviduct
male ejaculates 1.7 to 3.5
billion spermatazoa
Sperm swim toward
infandibulum in 30 minutes
may fertilize an ovum
immediately
but remains viable
for weeks
domestic fowl can lay fertile eggs 72 days after copulation
Laysan Duck
unfertilized eggs can
develop
most die
what sex would they be?
Egg production
birds are all oviparous -
body too hot for embryonic development?
glandular epithelial cells
of oviduct add
albumen-in magnum region - 3 hrs
shell membranes-in isthmus region - 1 hr
shell and pigmentation - 20 hrs.
takes about 24 hrs
3-4 hours in oviduct -
albumen - part of albumen
anchors yolk
shell membranes - porous
19-20 hrs in uterus where shell is formed
mostly calcium carbonate
(CaCO3)
where pesticides can affect
reproduction Diversion on why yolks are yellow.
Carotenoid pigments
Must be incorporated from diet-only by plants some bacteria and fungi
Conspicuous in sexual signals of many animals and may be related to
health.
Powerful antioxidants and immunostimulants
Protect vulnerable tissues from damage by free radicals (Reptile eggs use protein as the main energy source--this is not as high in energy as lipids--and doesn't produce as much metabolic water.) V.
The
Amazing Avian Egg.
usually 1-2 days between
eggs, can be 4-8
eggs range from 0.2 g to 9
kg of elephant birds
usually 2-11% body mass -
(Kiwis an amazing 40%!)
clutch size
depends on
nutrition
daily requirements range
from
40-50%
basal metabolic rate
125-180%
bmr
greatest need during yolk
formation
greatest for precocial young
genetics
varies within species
across species 1 - 23
determinant vs.
indeterminate layers
shapes and color - dictated
by nest structure in part
variation inspired
oologists
huge collections
19th century heyday
indian story
structure - cleidoic
porous - gas exchange to
embryo
water loss
CO2 content of
airspace
freed reptiles from aquatic
reproduction
reptiles eggs leathery -
can absorb water
increased calcification
adds protection
cost is loss of ability to absorb water
compensation is high water content of albumen-principal energy storage is
fat yields more H20 than protein energy storage of reptiles
embryonic needs
O2
get rid of CO2
H2O
- provided by albumen (90% water)
get rid of nitrogenous
wastes
uric acid again is important-water soluble forms of N would be
intolerable inside egg
high, constant temperature
physical protection - shell
very strong
biotic protection
- pores too small for viruses or bacteria to pass through - interior of egg one
of the most sterile environments
extra-embryonic membranes
shell membranes
vitelline membrane around
yolk
stomach & intestines
rich in lipids (21-36%) and protein (16-22%)
chorion
allantois
chorioallantois
site of gas exchange
blood vessels develop - candling eggs shell structure
cuticle - mostly protein,
part of biotic shield
palisade layer
mammilary cone
shell structure an exquisite compromise
extremely strong from
outside
easy to break form inside
more pores -> easier gas
exchange but unacceptable water loss
air space
gets higher in CO2
concentration
fills lungs of young at
hatch
embryo mobilizes calcium
from shell, which increases porosity as embryo needs more O2
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