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Ch' 17 Macroevolution

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calibrate (e.g., hemoglobin) measure rate of evolution among ... compare sequences of vertebrate and invertebrates to infer divergence time ... anagenesis? ... – PowerPoint PPT presentation

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Title: Ch' 17 Macroevolution


1
Ch. 17 Macroevolution

2
  • Prior to the Cambrian 543 Ma
  • Ctemophora
  • Cnidaria
  • Ctenophora
  • After the Cambrian
  • Suddenly everything else

3
  • molecular clocks
  • calibrate (e.g., hemoglobin) measure rate of
    evolution among vertebrates with known fossil
    ages
  • compare sequences of vertebrate and invertebrates
    to infer divergence time
  • Independent studies
  • Runnegar 82
  • Levinton and Shapiro 96

4
  • What was the Cambrian explosion?
  • Independent molecular clocks date divergences
    (Ba)
  • 1.2 proto/deuterostomes
  • 1
  • 500 million year discrepancy between fossil
    record and independent molecular clocks

5
  • Cambrian ecological explosion?
  • Due to
  • Rising O2 larger, more energetic organisms
  • Mass extinction opened niches
  • Neoproterozoic fauna were poor fozzilizers

6
  • Rates of evolution
  • Darwin predicted gradual change
  • The actual pattern in the fossil record often
    looks like (a)
  • morphological change is associated with
    speciation
  • circularity morphology defines species in fossil
    record

7
  • Avoiding circularity ancestral and derived
    species co-occur (e.g. bryozoans)
  • O and P co-occur over time therefore speciation
    can be inferred
  • R and S dont co-occur over time is S a new
    species or did R rapidly evolve into S
    (resolution 150k years)
  • Conclusions
  • stasis very high
  • change often associated with bifurcation
    (speciation)
  • speciation or anagenesis?

8
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Punctuated equilibrium (Eldredge and Gould 72)
  • epistatic genetic relationships prevent
    substantial evolution
  • coadaptation disrupted by founder event (genetic
    revolution)

9
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Punctuated equilibrium
  • epistatic genetic relationships prevent
    substantial evolution
  • coadaptation disrupted by founder event (genetic
    revolution)
  • Implications
  • evolution occurs by species selection not by
    genotype selection within populations

10
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Punctuated equilibrium
  • epistatic genetic relationships prevent
    substantial evolution
  • coadaptation disrupted by founder event (genetic
    revolution)
  • Implications
  • evolution occurs by species selection not by
    genotype selection within populations
  • Why this is frass
  • Tremendous number of examples of populations
    evolving substantially without speciating
  • Stasis is overstated fluctuation occurs about a
    mean, implying stabilizing selection

11
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Punctuated equilibrium
  • epistatic genetic relationships prevent
    substantial evolution
  • coadaptation disrupted by founder event (genetic
    revolution)
  • Implications
  • evolution occurs by species selection not by
    genotype selection within populations
  • Why this is frass
  • Tremendous number of examples of populations
    evolving substantially without speciation
  • Stasis is overstated fluctuation occurs about a
    mean, implying stabilizing selection
  • habitat selection in animals can contribute to
    stasis
  • Resolution of fossil record is rarely lt 100,000
    years substantial opportunity for transitions
  • Individual selection should be much faster than
    species selection b/c of greater opportunity
  • Genetic mechanisms undocumented

12
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Speciation preserves change (Futuyma, 1987)
  • 1. different populations are regularly diverging
    to local conditions

time
pop A pop B
habitat A habitat B
morphological trait value
13
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Speciation preserves change (Futuyma, 1987)
  • 1. different populations are regularly diverging
    to local conditions

time
pop A pop B
habitat A habitat B
morphological trait value
14
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Speciation preserves change (Futuyma, 1987)
  • different populations are regularly diverging to
    local conditions
  • these populations are usually brought back
    together before reproductive isolation
  • recombination (interbreeding) erases divergence

pop A pop B
time
pop A pop B
habitat A habitat B
recombination
morphological trait value
15
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Speciation preserves change (Futuyma, 1987)
  • different populations are regularly diverging to
    local conditions
  • these populations are usually brought back
    together before reproductive isolation
  • recombination (interbreeding) erases divergence

pop A pop B
time
pop A pop B
habitat A habitat B
recombination
morphological trait value
16
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Speciation preserves change (Futuyma, 1987)
  • 1. different populations are regularly diverging
    to local conditions
  • 2. these populations are usually brought back
    together before reproductive isolation
  • 3. recombination (interbreeding) erases
    divergence
  • 4. rarely, reproductive isolation evolves before
    (2) in which case morphological changes are not
    erased by recombination and possibly preserved in
    the fossil record

reproductive isolation
time
pop A pop B
habitat A habitat B
No recombination
morphological trait value
17
  • Conclusions stasis very high change often
    associated with bifurcation (speciation)
  • Why?
  • Speciation preserves change (Futuyma, 1987)
  • different populations are regularly diverging to
    local conditions
  • these populations are usually brought back
    together before reproductive isolation
  • recombination (interbreeding) erases divergence
  • rarely, reproductive isolation evolves before (2)
    in which case morphological changes are not
    erased by recombination and possibly preserved in
    the fossil record
  • Consistent with fossil record, extant
    observations, and population genetic theory
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