V. SPECIATION

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V. SPECIATION   A. Allopatric Speciation   B.
Parapatric Speciation (aka Local or
Progenitor - Derivative)   C. Adaptive
Radiation   D. Sympatric Speciation
Polyploidy
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A. Allopatric Speciation   different homes
  1. subdivision   a. geographic isolation
-- non-biological   b. extinction of
intermediate pops.   c. result NO GENE FLOW

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2. gradual accumulation of mutations   3.
genetic divergence over time   4. reproductive
isolation follows divergence BUT  5.
intercontinental disjunct congeners in plants are
fertile! e.g. Datisca, Platanus, Magnolia,
Liriodendron, etc.
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Platanus
P. orientalis SW Asia
P. occidentalis SE USA
P. acerifolia
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Datisca glomerata California
Datisca cannabina SW Asia
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Neis genetic identity 0.142
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Molecular Clocks I.Molecular divergence is
positively correlated with time (Zuckerkandl
Pauling, 1965) A. difficult with protein data
not neutral B. today there is abundant DNA
data, but the accuracy of molecular clocks is
questionable e.g. Hillis et al. 1996, Molecular
Systematics p. 531-541
r K / 2T r rate for neutral mutations T
divergence time K number of substitutions per
site
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• II. Clock Calibrations the Achilles heal
• Estimates of T are never precise,
• subject to under and overestimates
• 1.volcanic islands
• e.g. Hawaii, Canary Islands
• 2.biogeographic reconstruction
• a. Gondwanan and Laurasian distributions
• b. 2-25 mya estimates for 12 E. Asian- E. N.
  Am. disjuncts see Wen ARES 30421-55, 1999
• c. long distance dispersal is always a
  possibility

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3. Fossils a. relationship to extant taxa
uncertain b. no unequivocal fossil DNA c. DNA
degradation confounds mutation rate
estimates III. Model-based approaches 1. see
Sanderson, 1998 (Mol. Syst. Plants 2) for an
introduction 2. take into account the
stochasticity of divergence estimates, and
imprecision of time estimates
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B. Local Speciation (Progenitor -
Derivative) Parapatric Speciation   1.
isolation   a. migration   b. long
distance dispersal   c. peripheral population
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2. genetic bottlenecks   a. population
reduction   b. increased inbreeding genetic
drift   c. adaptation ?? maybe, maybe
not   i.e. selection pressure could cause the
fixation of genetic differences, but so might
random events 3. examples of adaptation a.
edaphic endemics serpentine, limestone, heavy
metals b. pollinators
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4. fixation of mutations between
populations a. with or without reproductive
isolation   b. faster than allopatry   c.
reduced genetic diversity in derivative   d.
relatively high genetic identity betw.
progenitor derivative  
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5. Chromosomal Rearrangements   a.
rearrangement established e.g.
translocation   b. hybrid sterility   ex.
Clarkia species (H. Lewis L. Gottlieb)  
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6. Mating System Change   a. self-compatibility
arising from self-incompatibility   e.g.
Stephanomeria malheurensis Oregon endemic,
described in 1975  
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C. Adaptive Radiation     1. open habitats
  2. little competition   3. radiation into
new ecological niches -   4. often w/o genetic
reproductive isolation   5. generally w/o much
genetic divergence   6. can result in a star
phylogeny
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Hawaiian tarweed adaptive radiation
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Rapid diversification, inferred from short
branches unresolved polytomy