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
