External Fertilization

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External Fertilization

• WFSC 422 Ethology
• Presentation 8.2

Dr. Jane M. Packard, WFSC TAMU j-packard_at_tamu.edu
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What is external fertilization?

• Eggs sperm both released outside bodies
• Fertilization occurs in water
• More instinctive than learned
• Typical of ancient species
• Also modern adaptations to
• Unpredictable land environments (treefrog)
• Predictable predation (fish)

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Example- sea urchin
source Arriving Trials of Life
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Oceanic ancestors

• PC Mechanisms
• Males release sperm into the ocean
• Females release eggs (millions)
• UF Functions
• Recombinant DNA- diversity
• Planktivore predator swamping
• Lottery analogy- chance patchy environments

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Herring (predator swamping)
source Arriving Trials of Life
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Oceanic ancestors

• PC Mechanisms
• Schooling fish move to coast
• Sperm eggs released at same time
• UF Functions
• Recombinant DNA
• Lottery analogy
• Widespread dispersal
• Shorebird predator swamping

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Example- Xmas Island crabs
source Arriving Trials of Life
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Oceanic ancestors

• PC Mechanisms
• Synchronized by moon high tide
• Land crabs- move to ocean
• Release eggs sperm into water
• UF Functions
• Recombination of DNA
• Lottery analogy
• Widespread dispersal between islands

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Example Trinidad treefrog
source Arriving Trials of Life
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Unpredictable land conditions

• PC Mechanisms
• Male treefrog holds female in amplexus
• Female lays egg in curled leaf
• Male releases sperm
• After eggs hatch, tadpoles drop in pond
• UF Functions
• Recombinant DNA
• Mate guarding/ egg protection
• Optimal conditions related to seasonal rain

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Example- Midas cichlid
source Arriving Trials of Life
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Predictable predation (UF)

• PC Mechanisms
• Male nest digging guarding
• Female spawns on rock male fertilizes
• Transfer hatchlings to nest oxygenation
• Swimming fry feed on mucous
• UF Functions
• Optimal conditions for fry- stable environment
• Nest guarding- paternity assurance
• Reduce risk of predation on fry

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SUMMARY function (example)

• H1 ancestral trait (e.g. sea urchin, herring,
  Xmas Is. Crab)
• H2 derived trait unpredictable land
  environments(treefrog)
• H3 derived trait predictable predation (midas
  cichlid)

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Action Items

• Do answers for Q8.3, Q8.4
• Search idealibrary for external fertilization
  Ryan, Michael J
• Search Animal Behavior for treefrog
• Post examples and sources on WebCT Discussion for
  Unit 8