1. Reproductive Biology of Elasmobranchs
Presented by:
Cori Jobe & Tricia Meredith

2. Introduction Reproduction has proceeded along only a few paths
Great diversity among congeners
- Brood sz., ovarian cycle, gestation period, mating system, nursery
Reproductive processes for most sharks are unknown

3. Introduction Primitive mode in fishes – broadcast spawning & oviparity
Embryos of oviparous fishes:
- Have small amt. of yolk
- Hatch in undeveloped condition
- Highly vulnerable
- Suffer heavy mortality
Reproductive adaptations contribute to evolutionary success
- Diverse group with continuum of reproductive strategies

4. Internal Fertilization
All elasmobranchs have internal fertilization
Females retain fertilized eggs for varying amts. of time
- Oviparous
- Viviparous
Bypassing larval stage:
- Reduces losses to predation
- Young have greater # of potential prey

5. Oviparity Eggs enclosed in cases & deposited No further parental care
Nourished solely by yolk
Slit in case allows for ventilation & oxygenation
R. erinacea egg case

6. Oviparity Oviparous elasmobranchs are:
- Benthic
- Littoral or bathyal
- Usually small
Produce small young – limited amt. of nutrients
Found only in:
- Heretodontidae, Scyliorhinidae, Orectolobidae
- Rajiiformes
Probably ancestral condition in sharks
Swell shark egg case
Juvenile swell shark emerging

7. Viviparity Retain embryos in uterus Embryos born fully developed
Aplacental viviparity
- Yolk dependency
- Oophagy
- Placental analogue
Placental viviparity

8. Aplacental Viviparity
No placental connection between mother and offspring
Previously called ovoviviparity
Variation in modes of embryo nourishment
Ultrasound of egg cases in nurse shark
Sonogram of embryo, post-hatching

9. Yolk Dependency Embryos depend solely on yolk deposited in egg
Do not receive supplemental nourishment from mother during gestation
Retained in uterus for protection
Young are relatively small at birth
Nurse shark uterus

10. Porbeagle embryo with yolk stomach
Oophagy
Large ovary, small eggs
Most eggs exist to nourish developing young
Embryos dependent on yolk for short amt. of time, then begin to ingest other eggs
C. taurus produces “feeding egg cases”
C. taurus utilizes uterine cannibalism
Porbeagle embryo with yolk stomach

11. Placental Analogues
Regions of uterine epithelium that secrete “uterine milk”
Embryotroph secreted by long villi, called trophonemata on uterine lining
Common in rays

12. Placental Viviparity Nourished by yolk sac 1st few weeks
Yolk sac then elongates & become vascularized
Tissues of yolk sac & uterine wall grows together, forming the placenta
Nutrients shunted from mother to embryo

13. Male Reproductive System
Seminal vesicles
Testes
Genital ducts
Efferent ducts
Epididymides
Ampullae epididymis
Urogenital papilla
Siphon sacs
Claspers
Testes
[bonnethead]
Claspers
[Skate]

14. Testes Paired symmetrical structures where sperm is produced
Vary greatly in size during the year and life cycle
Vary among species in morphology and functional arrangement

15. Developmental process
Testis
Ampullae
Spermatocyst
Spermatoblasts
Sertoli cells
Germ cells
Spermozeugma
Spermatophores

16. Ductus efferens
Leydig gland
Epididymis
Ampullae
epididymis
Testes
Ductus deferens
Liver
[spiny dogfish]

17. [dogfish] Ductus deferens Seminal vesicle Sperm sac Marshall’s gland
Urogenital sinus
Cloaca
Urogenital papillae
Clasper
[dogfish]

18. Claspers Paired copulatory organs
Rhipidion
Paired copulatory organs
Form articulations with the pelvic fin upon reaching maturity
During copulation, only one clasper is inserted into the female
A grip on the right pectoral fin positions the female on the male’s left, and the right clasper would be used
Terminal rhipidion serves to anchor the clasper within the reproductive tract of the female (hook or spine)
Sperm is ejected via siphon sacs
Speculation that they may serve to flush the female reproductive tract of semen from previous matings
Clasper
Pelvic fin
Siphon sac
[whitetip reef shark]

19. Mature male?
testis
Ducts deferens
clasper
However, the calcification and rigidity of the clasper, and the ability of the rhipidion to splay open and erect the spur are the best standards for determining maturity in male elasmobranchs.
Immature male
seminal vesicle
Mature male

20. Female Reproductive System
Pelvic fin
Cloacal opening
Ovaries
Oviducts
Ostium
Vagina
Uterus
Oviducal (shell) gland
Ovary
Oviduct
Liver
[blue shark]

21. Ovaries Paired or single structures where ova are produced
Usually both are fxnal, while in galeoid forms only the right is fxnal
Vary among species in morphology and functional arrangement

22. Oviducal (shell) gland
Elasmobranch Ova
Generally large and full of yolk
Oophagous lamnoid sharks
Produce large #’s of small eggs
2 eggs ovulated, 1/oviduct
Oviparous sharks
Egg case provides protection
Viviparous sharks
Egg case incorporated into placenta
Part of the ova not cleaved becomes the yolk sac
Oviducal (shell) gland
Uterus
Ovary
Ova
[spiny dogfish]

23. Sperm Storage Fertilization occurs prior to encapsulation
[salmon shark]
Fertilization occurs prior to encapsulation
Sperm stored in shell gland
Storage times range from 4 wks- >1yr
Lamniformes show no evidence of long-term storage
Lumen

24. Reproductive Cycles Complex and poorly understood Ovarian cycle
How often a female develops a batch of oocytes and ovulates a batch of eggs
Gestation period
Length of time between fertilization and parturition
Concurrent or consecutive?
Some species reproduce every 2 yrs (biennial)
Some species have annual cycles, where females carry developing oocytes and embryos at the same time
Reproductive cycles >3.5 yrs have been postulated

25. Mature female? Immature Mature Ovaries small
Shell gland appears as slight swelling
Vagina sealed by hymen
Mature
Ovaries large with bright yellow oocytes
Shell gland several times the diameter of the oviducts
[bull shark]

26. Mating & Reproductive Behavior
Courtship bites may signal male intent
Precopulatory behaviors result in male grasping female for clasper insertion
Females may be selective
Males may cooperate
Multiple paternity may occur

39. Conclusion
General trend from oviparity to viviparity with small #s of fully developed young
Reproductive adaptations that made them successful now threaten their survival
Understanding reproductive biology can help shape conservation & management

40. References
Carrier JC Identification and closure of nurse shark breeding grounds. The IUCN/SSC Shark Specialist Group. hark News 6: March.
Carrier JC, Murru FL, Walsh MT & Pratt HL Assessing reproductive potential and gestation in nurse sharks (Ginglymostoma cirratum) using ultrasonography and endoscopy: an example of bridging the gap between field research and captive studies. Zoo. Biol. 22:
Castro JI The biology of the nurse shark, Ginglymostoma cirratum, off the Florida east coast and the Bahama Islands. Environ. Biol. Fish. 58: 1-22.
Pratt HL & Carrier JC A review of elasmobranch reproductive behavior with a case study on the nurse shark, Ginglymostoma cirratum. Environ. Biol. Fish. 60: