Natural History of Sharks, Skates, and Rays Reproductive Biology MARE 380 Dr. Turner

1. Natural History of Sharks, Skates, and Rays Reproductive Biology MARE 380 Dr. Turner

2. Reproductive Biology Reproductive adaptations have contributed to evolutionary success & genetic continuity Reproductive processes for most sharks remains unknown

3. Fish Reproduction Primitive model for fish reproduction – oviparity ↑ large numbers of eggs & sperm are shed into the water - where fertilization occurs Typical of bony fishes

4. Fish Reproduction Oviparity - primitive model for fish reproduction – typical of bony fishes ↑ large numbers of eggs & sperm are shed into the water - where fertilization occurs Embryos – small amount of yolk; hatch undeveloped Eggs & young highly vulnerable to predators & environmental factors

5. Elasmobranch Reproduction Depart from simple oviparity: Internal fertilization Small numbers of large young Young born active, fully developed Develop during critical stages within ♀ ↑ size young, ↓ # potential predators r-selected species many, smaller offspring K-selected species fewer, larger offspring

6. Elasmobranch Reproduction Mating associated with ∆ in temperatures Reproductive cycles exist; details unknown Some sharks reproduce: - all year round - annually - alternate between resting periods

7. Elasmobranch Reproduction Mating involves aggressive courtship - ♂ bites ♀ to hold her into position In small sharks: ♂ wraps body around ♀ In large sharks: ♂ parallel to ♀

8. Love Bites! Aggressive courtship leads to scars & adaptation in ♀ Immature ♀ Mature ♀ Mature ♂

9. Elasmobranch Reproduction Ladies need a thicker skin… ♂ ♀ To counter ♂ aggression, ♀ sharks are larger and have up to 2X thicker epidermis

10. Elasmobranch Reproduction All have internal fertilization Ensures energy-expensive eggs not eaten Energy passed to embryos; not wasted 2 Groups: Oviparous (egg-laying), Viviparous (live-bearing)

11. Elasmobranch Reproduction Male (♂) pathway: Testicle (sperm produced) – epididymis – vas deferens – seminal vesicle- sperm sac – cloaca

12. Elasmobranch Reproduction Male (♂) pathway: Clasper draws in water – enters cloaca/vagina – opens like umbrella (anchor) – siphon contracts – expels H2O & sperm

13. Elasmobranch Reproduction Female (♀) pathway: Ova produced in both or just right ovary – released into abdominal cavity – cilia draw into oviduct – reach nidamental (shell gland – secretes “shell”) where fert takes place – down to uterus until egg laid or hatch/birth

14. Elasmobranch Reproduction Female (♀) pathway: Ova produced in both or just right ovary – released into abdominal cavity – cilia draw into oviduct – reach nidamental (shell gland – secretes “shell”) where fert takes place – down to uterus until egg laid or hatch/birth

15. Oviparous Forms Enclose eggs in tough horny egg case Incubation – months to over a year Oviparous (egg-laying) elasmobranchs – benthic, 1° littoral or bathyal, rarely large*

16. Oviparous Forms Whale shark found in the Gulf of Mexico in 1953; 30x14x8 cm (12x51/2x3 inches)

17. Oviparous Forms Whale shark harpooned in Taiwanese fishery - 300 embryos developing inside thin egg cases within the mother Determined whales sharks - ovoviviparous; eggs hatch within the uterus of the mother and remain until development is complete

18. Oviparous Forms 3 families of sharks: Heterodontidae, Scyliorhinidae, & Orectolobidae & Skates: Rajiformes

19. Viviparous Forms Retain embryos in uterus during entire development Divided into placental & aplacental; depending upon placental connection b/w ♀ & offspring

20. Aplacental Viviparity No placental connection (formerly ovoviviparity) Modes of nourishment vary widely: 1) depend upon yolk reserves 2) are oophagous (egg-eating) 3) are nourished via placental analogues

21. Yolk Dependency Embryos depend solely upon yolk deposited in egg at time of fertilization – no supplemental Relatively small at birth Include Squaliformes, Hexanchiformes, Squantinaformes, etc

22. Compartmentalization Life History strategy – one embryo – one uterus; leaves only 2 offspring… therefore, subdivide… Eliminates - oophagy

23. Oophagy Ovaries grow to tremendous size Eggs small; most exist to nourish young First few weeks – utilize yolk form own egg After – ingest other eggs in the uterus Some produce single (thresher) or multiple embryos (sandtiger – 12) per oviduct

24. Thunderdome! Bigeye Thresher Shark – No compartmentalization One uteri – one surviving embryo Many embryo enter – one embryo leave…

25. Placental Analogues “Uterine milk” (embryotroph/histotroph) is produced by long villi (trophonemata) Common in rays

26. Placental Viviparity Embryos nourished by yolk in yolk sac during first few weeks Once exhausted – yolk sac elongates and distal surface vascularized – touches uterine wall Grows into placenta – nourished now directly from female

27. Success!