foraminifera: part 3 - dimorphism. dimorphism dimorphic life cycle is complex –alternation of...
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PART 3 - DIMORPHISM
DIMORPHISMDimorphic life cycle is complexAlternation of sexual and asexual generationsMicrospheric formMegalospheric I formTrimorphism may be presentAdd a megalospheric II formCreates taxonomic problemsSome once designated as separate speciesSome were even designated as separate genera
DIMORPHISMMicrospheric formLargerMore chambersSmaller proloculusEarly stages may be differentIllustrates "ontogeny recapitulates phylogeny"Megalospheric formSmallerFewer chambersLarger proloculusEarly stages missing
Alternation of GenerationsDuration of a cycle varies1 year in tropics2-3 years at higher latitudesCycle stages varyAmong different ForaminiferaShort circuits occurMicrospheric (asexual or agamont or schizont) formDiploid & MultinucleatedReproduces asexuallyUsually during the winterProtoplasm withdrawsMeiosis (reduction division) occursHaploid cells producedProloculus formsRelease of young megalospheric (gamont) forms
Alternation of GenerationsMegalospheric (gamont) formOne nucleus until reproductionMatures during the summerWithdraws protoplasm and undergoes mitosisHaploid, biflagellated gametes producedSame haploid chromosome number as parentReleased from test of parent which emptiesGametes fuse with gametes from another gamontDiploid zygote (first cell) resultsSecretes a small proloculusZygote develops a microspheric test (agamont or schizont)
Foram Life CycleAlternation of generationsMegalosphericMicrospheric(= agamont)
Foram Life CycleAlternation of generations
Alternation of Generations
Agamontic Asexual Reproductions May Repeat Many Times
DimorphismWhat is the 3rd mode on this curve?(sexual)
DimorphismCornuspira sp. with embryonic coil at the center of the microspheric form that is lacking in the megalospheric form
DimorphismSummary comparison between microspheric and megalospheric tests of the same species
Examples of TrimorphismTrimorphism: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 stagesF) Megalospheric II biloculine stage only (largest proloculus)
END OF FILEVulvulina sp.Is this microspheric or megalospheric?
Last 2 chambers
Middle 12 chambers
First 4 chambers