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4603133 Overview of Sexual Reproduction in Sharks

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Overview of Sexual Reproduction in
Sharks
Cindy A Tribuzio
UW School of Aquatic and Fisheries Sciences
Discussion Outline
• Introduction
• Basic Shark
Reproduction
• Lamna ditropis,
Squalus acanthias
reproduction
• Research Areas
– Reproductive
Anatomy
– Hormone
Concentrations
– Uterine
Examinations
– Shell Gland
Histology
Shark Reproduction
• All elasmobranchs are internally fertilized
Variations in Reproduction
• Population
Structures-separation
of sexes
• Seasonality
• Different
Reproductive
Strategies
– Oviparity
– Viviparity
– Aplacental vivparity
Male Reproductive System
Male Internal Anatomy
Female Reproductive System
Female Internal Anatomy
Uterus, Ovaries, Shell Gland, etc
Oviparity “egg-laying”
• After mating occurs,
fertilized eggs are
encapsulated
• Shell structure varies
• Anchoring
• Incubation time
• No larval stage
Hatching
Viviparous-”placental”
• Used by about 10% of shark species
• After fertilization, eggs are encapsulated in
tertiary egg (this eventually develops into
the “placenta”)
• Shell glands much smaller, but
morphologically similar
• Early embryonic development occurs in
egg, within the uterus (no implantation)
• During mid gestation, yolk begins to
degenerate
• Placenta forms during latter stages of
gestation (paraplacenta)
• In most species, nutrient exchange has to
occur across an egg membrane
Uterine Structure
Placental Blue Shark
Undifferentiated Uterus
Developing Ovary
Immature
Yolked eggs
Fertilized Egg
Mature
Early Gestation
Mid
Late
Yolk Stalk Becomes
Umbilical Cord
Placenta Forms
Ovovivparous (aplacental vivparity)
• 3 types:
– Aplacental yolk sac
– Aplacental with trophonemata
– Aplacental with oophagy and intrauterine
cannibalism
Aplacental Yolk-Sac
• Embryo
develops in the
uterus
• Nourished via
yolk sac
• High number of
young produced
Aplacental with Trophonemata
• Relatively few, large, young develop in the
uterus
• Uterus is highly vascularized, and has a
very high surface area due to
trophonemata
• Secretion of histotroph
Aplacental with oophagy and
intrauterine cannibalism
• Exclusive to a few species
of Lamnidae sharks.
• Early development is similar
to aplacental yolk-sac.
• After that, they are
nourished by the yolk in
ovulated eggs
• The sand tiger shark,
practices intrauterine
cannibalism
• Smaller number of offspring
Lamna ditropis Reproduction
• Usual size range caught: 6-7.5ft
• Distribution:Throughout the North Pacific,
recorded as far south as California
• Partially endothermic: maintains body
temp ~15F above ambient water temp
• Ovovivparous, oophagy, litters usually 4-5
pups
Sample Collections
Blood Hormone Concentrations
• Blood samples can be collected from
animals to be released as well as from
those sacrificed for further dissection.
• Analyzed by radio-immunoassay for
concentrations of estradiol, testosterone
and progesterone.
• Comparison to gonadosomatic index, for
correlation
[E2] vs. Length of L. ditropis
#01-34
[E2] (pg/ml)
1000.0
800.0
600.0
400.0
200.0
0.0
170
175
180
185
190
Length (cm)
195
200
Uterine Examinations
Sample from #01-34
Shell Gland Histology
Spiny Dogfish Reproduction
Importance of this Research
• Basic Biological
information on
species
• Regional/Seasonal
Differences
• Applications for
Management
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