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pec a on
o ay sques ons:I. How o o og stsrecogn zespec es II. Howdoesspeciationoccur? Mechanismsofisolation Mechanismsofdivergence
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I. Howdobiologistsrecognizespecies?Aspeciesisapopulationorgroupofpopulationsinwhichevolutionaryforcesareactingindependently.Speciationisasplittingevent:
Newspeciesarecreatedby:1.Geneticiso ation ac o gene ow2.Geneticdivergence(duetomutation,selection,anddrift) y oesgene c so a oncrea e evo u onar yindependentunits?
Whydoesgeneticdivergencecreatesynapomorphies?
No gene flow to have them become similar. Selection, mutation and drift
can now occur independently.
Because it leads to different traits that can be used as synamophies.
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UseofspeciesconceptsCriteriontoidspecies Advantages DisadvantagesBiologicalspeciesconcept
Morphospecies concept
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Monophyleticgroup(aka,
andALLofitsdescendants
Parap y etic group:anancestor
and
some,
but
not
all,
Polyphyleticgroup:shareatraitthatdidntexistinthecommonancestor.
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LanceletsTunicates
HagfishLampreys
Ray-finned fishes
Lobe-finned fish
Frogs & toadsSalamanders
MammalsLizards and snakes
TurtlCrocodiles(Dinosaurs &) Birds
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Anexampleofthephylogenetic speciesconceptAsianelephants
Africanele hants
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II.Howdoesspeciationoccur?A.Allopatric (differentland)speciation ,evolutionaryforceswillactonthemindependently.1.Dispersal(recallthatfoundereventstriggergene c r
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N.parvuluswes ern s an s
N.trifasciatusGenovesa(Floreana)
N.melanotis(SanCristobal)N.parvulus
Westernislands(Genovesa)
N.macdonaldi(Espaola)
Caribbean
SanCristobal
Floreana Espaola
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e.g.Rhagoletis pomonella (appleandhawthornflies).
2.Mechanismofdivergence:
Flies have a strong preference to scentof a fruit so they are more likely to
mate on that tree. Since they mate in
different habitats, there is reduced
gene flow.
Different environments between the two
trees, so they can now have independent
evolutionary forces.
Apple vs. Hawthorne:
-Time of year.
-Chemistry of fruit.
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e.g.Tragopogon mirus
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Tragopogon mirus
1.Mechanism
of
isolation:
2.Mechanismofdivergence:
Punchline:itispossibletostudy
Gametic barrier to reproductively
isolate. Diploid and tetraploid
would be triploid and they would
be reproductively isolated.
During Meiosis when homologs line
up, the 3 chromosomes would lineup one with another and one
alone.
