Natural History of Sharks, Skates, and Rays Metabolism & Energy MARE 394 Dr. Turner Summer 2009
Natural History of Sharks, Skates, and Rays Reproductive Biology MARE 394 Dr. Turner Summer 2008.
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Transcript of Natural History of Sharks, Skates, and Rays Reproductive Biology MARE 394 Dr. Turner Summer 2008.
Natural History of Sharks, Skates, and Rays
Reproductive Biology
MARE 394Dr. Turner
Summer 2008
Reproductive BiologyReproductive adaptations have contributed to evolutionary success & genetic continuity
Reproductive processes for most sharks remains unknown
Fish ReproductionPrimitive model for fish reproduction – oviparity
↑ large numbers of eggs & sperm are shed into the water - where fertilization occurs
Typical of bony fishes
Fish ReproductionOviparity - 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
Elasmobranch ReproductionDepart from simple oviparity:Internal fertilizationSmall numbers of large youngYoung born active, fully developedDevelop during critical stages within ♀↑ size young, ↓ # potential predators
r-selected species many, smaller offspringK-selected species fewer, larger offspring
Elasmobranch ReproductionMating associated with ∆ in temperatures
Reproductive cycles exist; details unknown
Some sharks reproduce: - all year round - annually - alternate between resting periods
Elasmobranch ReproductionMating involves aggressive courtship - ♂ bites ♀ to hold her into position
In small sharks:♂ wraps body around ♀
In large sharks:♂ parallel to ♀
Love Bites!Aggressive courtship leads to scars & adaptation in ♀ Immature ♀
Mature ♂
Mature ♀
Elasmobranch ReproductionLadies need a thicker skin…
♂ ♀
To counter ♂ aggression, ♀ sharks are larger and have up to 2X thicker epidermis
Elasmobranch ReproductionAll have internal fertilization
Ensures energy-expensive eggs not eaten
Energy passed to embryos; not wasted
2 Groups: Oviparous (egg-laying), Viviparous (live-bearing)
Elasmobranch ReproductionMale (♂) pathway:
Testicle (sperm produced) – epididymis – vas deferens – seminal vesicle- sperm sac – cloaca
Elasmobranch ReproductionMale (♂) pathway:
Clasper draws in water – enters cloaca/vagina – opens like umbrella (anchor) – siphon contracts – expels H2O & sperm
Elasmobranch ReproductionFemale (♀) 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
Elasmobranch ReproductionFemale (♀) 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
Oviparous FormsEnclose eggs in tough horny egg case
Incubation – months to over a year
Oviparous (egg-laying) elasmobranchs – benthic, 1° littoral or bathyal, rarely large*
Oviparous FormsWhale shark found in the Gulf of Mexico in 1953; 30x14x8 cm (12x51/2x3 inches)
Oviparous FormsWhale 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
Oviparous Forms3 families of sharks: Heterodontidae, Scyliorhinidae, & Orectolobidae
& Skates: Rajiformes
Viviparous FormsRetain embryos in uterus during entire development
Divided into placental & aplacental; depending upon placental connection b/w ♀ & offspring
Aplacental ViviparityNo placental connection (formerly ovoviviparity)
Modes of nourishment vary widely:1) depend upon yolk reserves2) are oophagous (egg-eating)3) are nourished via placental analogues
Yolk DependencyEmbryos depend solely upon yolk deposited in egg at time of fertilization – no supplemental
Relatively small at birth
Include Squaliformes, Hexanchiformes, Squantinaformes, etc
CompartmentalizationLife History strategy – one embryo – one uterus; leaves only 2 offspring…therefore, subdivide…
Eliminates - oophagy
OophagyOvaries grow to tremendous size
Eggs small; most exist to nourish young
First few weeks – utilize yolk form own eggAfter – ingest other eggs in the uterus
Some produce single (thresher) or multiple embryos (sandtiger – 12) per oviduct
Thunderdome!Bigeye Thresher Shark – No compartmentalizationOne uteri – one surviving embryoMany embryo enter – one embryo leave…
Placental Analogues“Uterine milk” (embryotroph/histotroph) is produced by long villi (trophonemata)
Common in rays
Placental ViviparityEmbryos 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
Success!