FORAMINIFERA: PART 3 - DIMORPHISM

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FORAMINIFERAPART 3 - DIMORPHISM
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DIMORPHISM

• Dimorphic life cycle is complex
• Alternation of sexual and asexual generations
• Microspheric form
• Megalospheric I form
• Trimorphism may be present
• Add a megalospheric II form
• Creates taxonomic problems
• Some once designated as separate species
• Some were even designated as separate genera

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DIMORPHISM

• Microspheric form
• Larger
• More chambers
• Smaller proloculus
• Early stages may be different
• Illustrates "ontogeny recapitulates phylogeny"
• Megalospheric form
• Smaller
• Fewer chambers
• Larger proloculus
• Early stages missing

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Alternation of Generations

• Duration of a cycle varies
• 1 year in tropics
• 2-3 years at higher latitudes
• Cycle stages vary
• Among different Foraminifera
• Short circuits occur
• Microspheric (asexual or agamont or schizont)
  form
• Diploid Multinucleated
• Reproduces asexually
• Usually during the winter
• Protoplasm withdraws
• Meiosis (reduction division) occurs
• Haploid cells produced
• Proloculus forms
• Release of young megalospheric (gamont) forms

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Alternation of Generations

• Megalospheric (gamont) form
• One nucleus until reproduction
• Matures during the summer
• Withdraws protoplasm and undergoes mitosis
• Haploid, biflagellated gametes produced
• Same haploid chromosome number as parent
• Released from test of parent which empties
• Gametes fuse with gametes from another gamont
• Diploid zygote (first cell) results
• Secretes a small proloculus
• Zygote develops a microspheric test (agamont or
  schizont)

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Foram Life Cycle

• Alternation of generations

Megalospheric
Microspheric
( agamont)
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Foram Life Cycle

• Alternation of generations

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Alternation of Generations
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Gamontogamy
Megalospheric
Microspheric
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Gamontogamy
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Asexual Reproduction
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Agamontic Asexual Reproductions May Repeat Many
Times
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Autogamy
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Gametogamy
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Dimorphism
(sexual)

• What is the 3rd mode on this curve?

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Dimorphism

• Cornuspira sp. with embryonic coil at the center
  of the microspheric form that is lacking in the
  megalospheric form

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Dimorphism
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Dimorphism

• Summary comparison between microspheric and
  megalospheric tests of the same species

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Examples of Trimorphism

• Trimorphism
• A) Nodosaria sp.
• B) Dentalina sp.
• C) Marginulina sp.
• Pyrgo sp.
• D) Microspheric quinqueloculine to triloculine to
  biloculine stages (smallest proloculus)
• E) Megalospheric I triloculine to biloculine
  stages
• F) Megalospheric II biloculine stage only
  (largest proloculus)

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END OF FILE

• Vulvulina sp.
• Is this microspheric or megalospheric?
• Last 2 chambers
• Middle 12 chambers
• First 4 chambers