Transcript Reproductive Biology of Elasmobranchs

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
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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
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•
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[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.