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Reproductive Biology of Elasmobranchs Presented by: Cori Jobe & Tricia Meredith 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 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 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 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 Oviparity • Oviparous elasmobranchs are: - Benthic - Littoral or bathyal - Usually small • Produce small young – limited amt. of nutrients • Found only in: Swell shark egg case - Heretodontidae, Scyliorhinidae, Orectolobidae - Rajiiformes • Probably ancestral condition in sharks Juvenile swell shark emerging Viviparity • Retain embryos in uterus • Embryos born fully developed • Aplacental viviparity - Yolk dependency - Oophagy - Placental analogue • Placental viviparity 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 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 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 Placental Analogues • Regions of uterine epithelium that secrete “uterine milk” • Embryotroph secreted by long villi, called trophonemata on uterine lining • Common in rays 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 Male Reproductive System 1. Testes 2. Genital ducts Seminal vesicles Testes – Efferent ducts – Epididymides – Ampullae epididymis 3. Urogenital papilla 4. Siphon sacs 5. Claspers [bonnethead] Claspers [Skate] 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 Testis Developmental process Ampullae Spermatocyst Spermatoblasts Sertoli cells Germ cells Spermozeugma Spermatophores Ductus efferens Leydig gland Epididymis Ampullae epididymis Testes Ductus deferens Liver [spiny dogfish] Seminal vesicle Sperm sac Ductus deferens Marshall’s gland Urogenital sinus Cloaca Urogenital papillae Clasper [dogfish] Claspers • Paired copulatory organs • Form articulations with the pelvic fin upon reaching maturity • During copulation, only one clasper is inserted into the female Rhipidion Clasper Pelvic fin – 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 Siphon sac – Speculation that they may serve to flush the female reproductive tract of semen from previous matings [whitetip reef shark] Mature male? testis Ducts deferens Immature male seminal vesicle Mature male 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. Female Reproductive System Cloacal opening 1. Ovaries 2. Oviducts Pelvic fin Ostium Vagina Uterus Ovary Oviducal (shell) gland Oviduct Liver [blue shark] 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 Elasmobranch Ova • Generally large and full of yolk • Oophagous lamnoid sharks – Produce large #’s of small eggs – 2 eggs ovulated, 1/oviduct • Uterus Oviducal (shell) gland Ovary Oviparous sharks – Egg case provides protection Ova • Viviparous sharks – Egg case incorporated into placenta – Part of the ova not cleaved becomes the yolk sac [spiny dogfish] Sperm Storage • • • • [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 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 Mature female? • Immature – 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] 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 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 References Carrier JC. 1996. Identification and closure of nurse shark breeding grounds. The IUCN/SSC Shark Specialist Group. hark News 6: March. http://www.flmnh.ufl.edu/fish/organizations/ssg/sharknews/sn6/shark6news9.htm Carrier JC, Murru FL, Walsh MT & Pratt HL. 2003. 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: 179-187. Castro JI. 2000. 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. 2001. A review of elasmobranch reproductive behavior with a case study on the nurse shark, Ginglymostoma cirratum. Environ. Biol. Fish. 60: 157-188.