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Speciation
I. Modes
II. Mechanisms
A. Progressive Genomic Incompatibility
B. Hybrid Incompatibility
C. Differential Selection
D. Hybridization
E. Polyploidy
E. Polyploidy
Autopolyploidy
Allopolyploidy
E. Polyploidy
Allopolyploidy
Spartina
Spartina alternifolia, native to US, was found in southern England
in late1800's. There is a European species Spartina maritima.
Early in the 20th century a sterile hybrid was found and was called
Spartina townsendii This went through a process of diploidization
(increased ploidy) and became a new sexually reproducing
species known as Spartina anglica
S. maritima
sterile hybrid
S. anglica
S. alterniflora
E. Polyploidy
Allopolyploidy
Speciation
I. Modes
II. Mechanisms
III. Rates
III. Rates
Mark Pagel,* Chris Venditti, Andrew Meade .2006. Large Punctuational
Contribution of Speciation to Evolutionary Divergence at the
Molecular Level . Science 314:119.
A long-standing debate in evolutionary biology concerns whether
species diverge gradually through time or by punctuational episodes
at the time of speciation. We found that approximately 22% of
substitutional changes at the DNA level can be attributed to
punctuational evolution, and the remainder accumulates from
background gradual divergence. Punctuational effects occur at more
than twice the rate in plants and fungi than in animals, but the
proportion of total divergence attributable to punctuational change
does not vary among these groups. Punctuational changes cause
departures from a clock-like tempo of evolution, suggesting that they
should be accounted for in deriving dates from phylogenies.
Punctuational episodes of evolution may play a larger role in
promoting evolutionary divergence than has previously been
appreciated.
Origin of Life Hypotheses
4.5 bya: Earth Forms
I. Earth History
I. Earth History
- Earliest Atmosphere - probably of volcanic origin
Gases produced were probably
similar to those created by
modern volcanoes (H2O, CO2,
SO2, CO, S2, Cl2, N2, H2) and
NH3 and CH4
4.0 bya: Oldest Rocks
4.5 bya: Earth Forms
I. Earth History
4.0 bya: Oldest Rocks
3.5 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
4.0 bya: Oldest Rocks
3.5 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
Stromatolites - communities of layered 'bacteria'
2.3-2.0 bya: Oxygen in
Atmosphere
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
0.5 bya: Cambrian
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
0.5 bya: Cambrian
0.24 bya:Mesozoic
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
0.5 bya: Cambrian
0.24 bya:Mesozoic
0.065 bya:Cenozoic
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
0.5 bya: Cambrian
0.24 bya:Mesozoic
0.065 bya:Cenozoic
0.9 bya: first animals
1.8 bya: first eukaryote
2.3-2.0 bya: Oxygen
4.0 bya: Oldest Rocks
3.4 bya: Oldest Fossils
4.5 bya: Earth Forms
I. Earth History
4.5 million to present
(1/1000th of earth
history)
II. Origin of Life Hypotheses
- Oparin-Haldane Hypothesis (1924):
- in a reducing atmosphere, biomonomers would form spontaneously
Aleksandr Oparin
(1894-1980)
J.B.S. Haldane
(1892-1964)
II. Origin of Life Hypotheses
- Oparin-Haldane Hypothesis (1924):
- in a reducing atmosphere, biomonomers would form spontaneously
- Miller-Urey (1953)
all biologically important
monomers have been
produced by these
experiments, even while
changing gas composition
and energy sources
II. Origin of Life Hypotheses
- Oparin-Haldane Hypothesis (1924):
- in a reducing atmosphere, biomonomers would form spontaneously
- Miller-Urey (1953)
- Sydney Fox - 1970 - polymerized protein microspheres
II. Origin of Life Hypotheses
- Oparin-Haldane Hypothesis (1924):
- in a reducing atmosphere, biomonomers would form spontaneously
- Miller-Urey (1953)
- Sydney Fox - 1970 - polymerized protein microspheres
- Cairns-Smith (1960-70) - clays as templates for non-random
polymerization
- 1969 - Murcheson meteorite - amino acids present; some not found on
Earth. To date, 74 meteoric AA's.
- 2004 - Szostak - clays could catalyze
formation of RNA's
III. Acquiring the Characteristics of Life
A. Three Primary Attributes:
- Barrier (phospholipid membrane)
- Metabolism (reaction pathways)
- Genetic System
III. Acquiring the Characteristics of Life
B. Barrier (phospholipid membrane)
- form spontaneously in aqueous solutions
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- problem:
how can pathways with useless intermediates evolve?
These represent 'maladaptive valleys', don't they?
A
B
C
D
How do you get from A to E, if B, C, and D are non-functional?
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
A
B
C
D
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
suppose E is a useful molecule, initially available in the env.
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
suppose E is a useful molecule, initially available in the env.
As protocells gobble it up, the concentration drops.
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
D
Anything that can absorb something else (D) and MAKE E is
at a selective advantage...
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
D
Anything that can absorb something else (D) and MAKE E is
at a selective advantage...
but over time, D may drop in concentration...
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
C
D
So, anything that can absorb C and then make D and E will
be selected for...
E
III. Acquiring the Characteristics of Life
C. Metabolic Pathways
- Solution - reverse evolution
A
B
C
D
and so on until a complete pathway
evolves.
E
III. Acquiring the Characteristics of Life
D. Genetic Systems
- conundrum... which came first, DNA or the proteins they
encode?
DNA
RNA
(m, r, t)
protein
III. Acquiring the Characteristics of Life
D. Genetic Systems
- conundrum... which came first, DNA or the proteins they
encode?
DNA
DNA stores info, but proteins
are the metabolic catalysts...
RNA
(m, r, t)
protein
III. Acquiring the Characteristics of Life
D. Genetic Systems
- conundrum... which came first, DNA or the proteins they
encode?
- Ribozymes
info storage AND
cataylic ability
III. Acquiring the Characteristics of Life
D. Genetic Systems
- conundrum... which came first, DNA or the proteins they
encode?
- Ribozymes
- Self replicating molecules
- three stage hypothesis
IV. Early Life
- the first cells were probably
heterotrophs that simply absorbed
nutrients and ATP from the
environment.
- as these substances became rare,
there was strong selection for cells
that could manufacture their own
energy storage molecules.
- the most primitive cells are
methanogens, but these are NOT
the oldest fossils.
IV. Early Life
- the second type of cells were probably like green-sulphur bacteria,
which used H2S as an electron donor, in the presence of sunlight, to
photosynthesize.
IV. Early Life
- the evolution of oxygenic photosynthesis was MAJOR. It allowed life
to exploit more habitats, and it produced a powerful oxidating agent!
These stromatolites, which date to > 3 bya are microbial communities.
IV. Early Life
- about 2.3-1.8 bya, the concentration of oxygen began to increase in
the ocean and oxidize eroded materials minerals... deposited as
'banded iron formations'.
IV. Early Life
- 2.0-1.7 bya - evolution of eukaryotes.... endosymbiosis.
IV. Early Life
Eukaryote Characteristics
- membrane bound nucleus
- organelles
- sexual reproduction
infolding of membrane
IV. Early Life
Origins
IV. Early Life
B. Origins
endosymbiosis - mitochondria and
chloroplasts (Margulis - 1970's)
IV. Early Life
Relationships among life forms - deep ancestry and the last "concestor"
IV. Early Life
Woese - r-RNA analyses reveal a
deep divide within the bacteria
IV. Early Life
IV. Early Life
IV. Early Life
Curiously, the very root of
life may be invisible to
genetic analysis. Bacteria
transfer genes by division
(to 'offspring'), but they also
transfer genes "laterally" to
other living bacteria. This
makes reconstructing
bacterial phylogenies
difficult.
IV. Early Life
So, reconstructing
the patterns of
relatedness
among these
ancient life forms
is difficult.
Different genes
give different
patterns of
relatedness
among domains
IV. Early Life
C. Domains - "Ring of Life" hypothesis (2004)