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Chapter 14 : The Origin of Species
Evolution is the source of biological diversity
Most changes are minor
Definition of species:
Linnaeus invented Genus species naming
system
But… it is complicated…
Some species look alike but can’t interbreed
Some vary greatly but can interbreed
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Species Concepts
Morphological Species Concept
Ecological Species Concept
Phylogenetic Species Concept
Biological Species Concept
Biological Species Concept
“Group of populations whose members
have the potential to interbreed in nature
and produce fertile offspring.” - Ernst Mayer, 1942
Systematics and the Origin of Species
Reproductive isolation
pre-zygotic
post-zygotic
inviable or infertile offspring
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Emma Hickerson, NYTimes
Speciation
Allopatric
Geographic barrier arrises
Populations diverge genetically
Genetic divergence accidentally
causes reproductive isolation
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Reinforcement
Controversial step
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If hybrids between 2 evolving species
are less fit - inviable or infertile, it
pays for females to be choosy
about mates.
=
Direct selection to evolve prezygotic isolation
Evidence
Koopman (1950), Coyne and Orr
(1989), Noor (1995)
Speciation
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Sympatric
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http://evolution.berkeley.edu
no geographic barrier
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Polyploidy
Speciation in one generation!
2N
4n
Caused by failure of cell division after
chromosome duplication
Most common in plants
auto vs allo-polyploidy
Fig. 14-5a-1
1
Parent species
2n = 6
Tetraploid
cells
4n = 12
Fig. 14-5a-2
2
1
Parent species
2n = 6
Tetraploid
cells
4n = 12
Diploid
gametes
2n = 6
Fig. 14-5a-3
3
2
1
Parent species
2n = 6
Selffertilization
Tetraploid
cells
4n = 12
Diploid
gametes
2n = 6
Viable, fertile
tetraploid
species
4n = 12
Fig. 14-5b-1
Species A
2n = 4
Species B
2n = 6
Gamete
n=2
Gamete
n=3
Fig. 14-5b-2
Chromosomes not
homologous
(cannot pair)
1
Species A
2n = 4
2
Gamete
n=2
Sterile hybrid
n=5
Species B
2n = 6
Gamete
n=3
Fig. 14-5b-3
Chromosomes not
homologous
(cannot pair)
1
Species A
2n = 4
2
3
Gamete
n=2
Sterile hybrid
n=5
Species B
2n = 6
Gamete
n=3
Viable, fertile
hybrid species
2n = 10
Fig. 14-6b
´
AA
Triticum monococcum
(14 chromosomes)
BB
1
Wild
Triticum
(14 chromosomes)
Hybridization
AB
Sterile hybrid
(14 chromosomes)
2
Cell division error
and self-fertilization
´
AA BB
DD
T. turgidum
Emmer wheat
(28 chromosomes)
T. tauschii
(wild)
(14 chromosomes)
3
Hybridization
ABD
Sterile hybrid
(21 chromosomes)
4
Cell division error
and self-fertilization
AA BB DD
T. aestivum
Bread wheat
(42 chromosomes)
Estimate that 80% of living plant
species arose by polyploidy
Many food crops
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Plant geneticists use chemicals that
cause mitotic and meiotic errors to
make more.
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Sympatric speciation in animals
Polyploid occurs occasionally
More likely through
habitat differentiation
sexual selection
Genetics of Speciation
2 major genetic modes of speciation
1. Polyploidy
2. Modern Synthesis
Modern Synthesis
Darwin’s Paradox
how to get through sterile stage?
Dobzhansky-Muller Model (1930)
the conflicting alleles never meet
Does Natural Selection Cause Speciation?
Evidence so far says:
The genes are in a variety of classes
Very rapidly evolving
Evolving by selection!
Reproductive barriers evolve
Dodd experiment
single genes
multiple genes
Fig. 14-7a
Initial sample
of fruit flies
Starch medium
Maltose medium
Female
Starch Maltose
22
9
8
20
Results
Mating frequencies
in experimental groups
Female
Population Population
#1
#2
Male
Pop#2 Pop#1
Maltose Starch
Male
Mating experiments
18
15
12
15
Mating frequencies
in starch control groups
Fig. 14-7b
Hybrid Zones
Coyne and Orr
Cichlids
Darwin’s finches
Adaptive Radiation
Evolution of many diverse species from one
common ancestor.
A few organisms colonize an unexploited
area
Or environmental changes cause
extinctions
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Phylogeny for Greater Antillean Anolis lizards showing reconstruction of microhabitat
specialization via maximum likelihood. Microhabitat divergence occurred relatively
early in the radiation. Subsequent speciation events have been associated with
differentiation along other resource axes.
R. Glor
www.lacertilia.com
Speciation Rates
Punctuated Equilibrium
SJ Gould and Eldridge
Gradual