Download Speciation

MACROEVOLUTION
AND SPECIATION
How did this
flightless
bird come to
live on the
isolated
Galápagos
Islands?
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Separation of the
Species
 Macroevolution
is
best
observed within the fossil
record,
 Requires the origin of
species, also called
speciation.
 Speciation is the final result
of changes in gene pool
allelic and genotypic
frequencies.
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2
Macroevolution: the origin of new taxonomic groups
Speciation: the origin of new
species
1- Anagenesis (phylogenetic
evolution): accumulation of
heritable changes
2- Cladogenesis (branching
evolution): budding of new
species from a parent species
that continues to exist (basis of
biological diversity)
Species Definitions
 Evolutionary species concept distinguish
species from one another based on:
 Morphological (structural) traits,
 Biological species concept relies primarily on
reproductive isolation rather than trait
differences to define a species.
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What is a species?
 Biological species
concept (ErnstMayr):
a population or group of
populations whose members
have the potential to interbreed
and produce viable, fertile
offspring (genetic exchange is
possible and that is genetically
isolated from other
populations)
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How and why do new
species originate?
 Species are created by a series of evolutionary
processes
 populations become isolated
 geographically isolated
 reproductively isolated
 isolated populations
evolve independently
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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
PREZYGOTIC BARRIERS
Reproductive Isolation (isolation of gene pools)
 Prezygotic barriers: impede mating
between species or hinder the
fertilization of the ova
 Habitat (snakes; water/terrestrial)
 Behavioral (fireflies; mate
signaling)
 Temporal (salmon; seasonal
mating)
 Mechanical (flowers; pollination
anatomy)
 Gametic (frogs; egg coat receptors)
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Habitat isolation: Species occur in same region, but
occupy different habitats so rarely encounter each other
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial
Leopon
http://ahgertz.wordpress.com/2010/07/28/zedonk-isawesome-hybrid-animals/
lions & tigers could
hybridize, but they
live in different
habitats:
 lions in grasslands
 tigers in rainforest
Temporal isolation: Species that breed at
different times of the day, different seasons, or
different years cannot mix their gametes
Eastern spotted skunk
(R) & western spotted
skunk (L) overlap in
range but eastern mates
in late winter & western
mates in late summer
Western spotted skunk
(Spilogale gracilis)
Eastern spotted skunk
(Spilogale putorius)
Behavioral isolation: Courtship rituals and other
behaviors unique to a species are effective
barriers
Courtship ritual of bluefooted boobies
Video: Albatross Courtship Ritual
Video: Giraffe Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
Mechanical isolation: Morphological differences
can prevent successful mating
For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
– lack of “fit” between sexual
organs:
hard to imagine for us… but a
big issue for insects with
different shaped genitals!
Bradybaena with shells
spiraling in opposite
directions
 Gametic isolation: Sperm of one species may
not be able to fertilize eggs of another species
Sea urchins
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
POSTZYGOTIC BARRIERS
 Postzygotic barriers prevent the hybrid
zygote from developing into a viable, fertile
adult:
 Zygote mortality (Reduced hybrid viability)
 Hybrid Sterility (Reduced hybrid fertility)
 F2 Fitness (Hybrid breakdown)
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Zygote mortality (Reduced hybrid
viability): Genes of the different parent species
may interact and impair the hybrid development
Ensatina hybrid
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Hybrid Sterility (Reduced hybrid fertility):
Even if hybrids are vigorous, they may be sterile
Donkey
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F2 Fitness (Hybrid breakdown): Some firstgeneration hybrids are fertile, but when they mate
with another species or with either parent species,
offspring of the next generation are feeble or sterile
Hybrid cultivated
rice plants with
stunted offspring
(center)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
REPRODUCTIVE
ISOLATION REVIEW
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Speciation can take place with
or without a geographic barrier
 Geographic
speciation can
occur in two
ways:
 Allopatric speciation
 Sympatric
speciation
(a) Allopatric speciation
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(b) Sympatric speciation
Allopatric
(Other
Country)
Speciation
 In allopatric speciation, gene flow is
interrupted or reduced when a population is
divided into geographically isolated
subpopulations
Evidence of Allopatric Speciation
• Regions with many geographic barriers
typically have more species than do regions
with fewer barriers
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Allopatric Speciation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lake male
River male
Lake female
River female
a. Sockeye salmon at Pleasure Point Beach, Lake Washington

b. Sockeye salmon in Cedar River .The river connects with
Lake Washington.
Salmon that matured at Pleasure Point Beach do not
reproduce with those that matured in the Cedar River.
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23
Adaptive Radiation
 Adaptive Radiation
 When members of a
species invade
several new
geographically
separate
environments
 The populations
become adapted to
the different
environments
 Many new species
evolve from the
single ancestral
species
 This is an example of
allopatric speciation
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Sympatric (“Same Country”)
Speciation
 In sympatric speciation, speciation takes
place in geographically overlapping populations
 Caused by chromosomal
abnormalities….abnormal number of
chromosomes
 Nonrandom mating (lowers gene flow)
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Polyploidy
 Polyploidy is the presence of extra sets of
chromosomes due to accidents during cell
division
• Polyploidy is much more common in plants
than in animals
• Many important crops (oats, cotton, potatoes,
tobacco, and wheat) are polyploids
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Autopolyploidy
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Allopolyploidy
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Alloploidy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
seeds
diploid
banana (2n)
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no
seeds
polyploid
banana
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Allopatric and Sympatric
Speciation: A Review
 In allopatric speciation, geographic isolation
restricts gene flow between populations
 Reproductive isolation may then arise by
natural selection, genetic drift, or sexual
selection in the isolated populations
 Even if contact is restored between
populations, interbreeding is prevented
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Patterns in the Fossil
Record
 The fossil record includes examples of species that
appear suddenly, persist essentially unchanged for
some time, and then apparently disappear
 Niles Eldredge and Stephen Jay Gould coined the
term punctuated equilibrium to describe periods
of apparent stasis punctuated by sudden change
 The punctuated equilibrium model contrasts with a
model of gradual change in a species’ existence
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Fig. 24-17
(a) Punctuated pattern
Time
(b) Gradual pattern
Speciation Rates
 The punctuated pattern in the fossil record and
evidence from lab studies suggests that
speciation can be rapid
 The interval between speciation events can
range from 4,000 years (some cichlids) to
40,000,000 years (some beetles), with an
average of 6,500,000 years
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Principles of Macroevolution
 Macroevolution
 Evolution at the species or higher level of classification
 Occurs gradually
 Evolutionists support a gradualistic model
 Speciation occurs after populations become isolated
 Each group continuing its own evolutionary pathway
 The gradualistic model suggests that it is difficult to
indicate when speciation occurred
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34
Principles of Macroevolution
 Macroevolution
 Some paleontologists believe that
 Species can appear quite suddenly
 Remain essentially unchanged phenotypically during a period
of stasis (sameness) until they undergo extinction.
 Based on these findings, they developed a punctuated
equilibrium model to explain the pace of evolution.
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35
Developmental Genes and
Macroevolution
 Genes can bring about radical changes in body shapes
and organs.
 Gene Expression Can Influence Development
 A change in gene expression could stop developmental process
or continue it beyond its normal time.
 Using modern technology researchers discovered genes whose
differential expression can bring about changes in body shapes
and organs.
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36
Pax6 Gene and Eye
Development
(Left): © Carolina Biological Supply/Photo Researchers, Inc.; (Center): © Vol. OS02/PhotoDisc/Getty Images; (Right): © Aldo Brando/Peter Arnold, Inc.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
37
Evolution is not
goal-oriented
An evolutionary trend does
not mean that evolution is
goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well
Remember that for
humans as well!
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Evolution is not
the survival of the
fittest. Rather it is
the survival of the
just good enough.
From Speciation to
Macroevolution
 Macroevolution is the cumulative effect of
many speciation and extinction events
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings