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8/14/2019 AP Bio Chapter 24.pdf
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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITIONJane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
2011 Pearson Education, Inc.
Lectures by
Erin Barley
Kathleen Fitzpatrick
The Origin of Species
Chapter 24
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Overview: That Mystery of Mysteries
In the Galpagos Islands Darwin discoveredplants and animals found nowhere else on Earth
Darwin referred to the origin of species as thatmystery of mysteries (1), and despite decades of
study, evolutionary biologists still cannot agree on
the underlying processes that have produced the
great diversity of life around us
2011 Pearson Education, Inc.
Video: Galpagos Tortoise
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Figure 24.1
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Speciation, the origin of new species, is at thefocal point of evolutionary theory (2)
Evolutionary theory must explain how new speciesoriginate and how populations evolve
Microevolutionconsists of changes in allelefrequency in a population over time
Macroevolution refers to broad patterns ofevolutionary change above the species level (3)
2011 Pearson Education, Inc.
Animation: Macroevolution
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Concept 24.1: The biological species
concept emphasizes reproductive isolation
Speciesis a Latin word meaning kind or
appearance
2011 Pearson Education, Inc.
The biological species concept states that aspecies is a group of populations whose members
have the potential to interbreed in nature and
produce viable, fertile offspring; they do not breed
successfully with other populations (4)
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L imitations of the Biological Species Concept
The biological species concept cannot beapplied to fossils or asexual organisms
(including all prokaryotes)
The biological species concept emphasizes
absence of gene flow
However, gene flow can occur between
distinct species
For example, grizzly bears and polar bearscan mate to produce grolar bears
2011 Pearson Education, Inc.
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Figure 24.4Grizzly bear (U. arctos )
Polar bear (U. mari t imus )
Hybrid grolar bear
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Reproductive I solation
Reproductive isolation is the existence ofbiological factors (barriers) that impede two
species from producing viable, fertile offspring
Hybrids are the offspring of crosses between
different species
Reproductive isolation can be classified by
whether factors act before or after fertilization
(5-6)
2011 Pearson Education, Inc.
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Figure 24.3_a
Prezygotic barriers
Habitat
IsolationTemporal
Isolation
Behavioral
Isolation
Mechanical
Isolation
Gametic
IsolationReduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
Individualsof
differentspecies
MATINGATTEMPT FERTILIZATION
VIABLE,FERTILE
OFFSPRING
Postzygotic barriers
(a) (c) (e)
(d)
(b)
(g)
(k)
(h) (i)
(j)
(l)(f)
(9)
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Prezygotic barriers block fertilization from
occurring by:
Impeding different species from attempting to
mate
Preventing the successful completion of mating
Hindering fertilization if mating is successful
2011 Pearson Education, Inc.
Postzygotic barriers prevent the hybrid zygote
from developing into a viable, fertile adult:Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown (7)
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Habitat isolation: Two species encounter each
other rarely, or not at all, because they occupy
different habitats, even though not isolated byphysical barriers
2011 Pearson Education, Inc.
Temporal isolation: Species that breed at
different times of the day, different seasons,
or different years cannot mix their gametes Behavioral isolation: Courtship rituals and other
behaviors unique to a species are effective
barriers Gametic Isolation: Sperm of one species may not
be able to fertilize eggs of another species Mechanical isolation: Morphological differences
can prevent successful mating (8 partial)
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Video: Blue-footed Boobies Courtship Ritual
Video: Giraffe Courtship Ritual
Video: Albatross Courtship Ritual
http://localhost/var/www/apps/conversion/tmp/scratch_5/24_03eAlbatrossCourtship_SV.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_5/24_03eGiraffeCourtship_SV.mpghttp://localhost/var/www/apps/conversion/tmp/scratch_5/24_03eBoobiesCourtship_SV.mpg8/14/2019 AP Bio Chapter 24.pdf
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Reduced hybrid viability: Genes of the differentparent species may interact and impair the
hybrids development
2011 Pearson Education, Inc.
Hybrid breakdown: Some first-generation hybrids
are fertile, but when they mate with anotherspecies or with either parent species, offspring of
the next generation are feeble or sterile (8 rest)
Reduced hybrid fertility: Even if hybrids arevigorous, they may be sterile
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Concept 24.2: Speciation can take place
with or without geographic separation
Speciation can occur in two ways:
Allopatric speciation
Sympatric speciation
2011 Pearson Education, Inc.
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Figure 24.5
(a) (b)Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.
(10)
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The Process of Allopatric Speciation
The definition of barrier depends on the ability of a
population to disperse (11)
For example, a canyon may create a barrier for
small rodents, but not birds, coyotes, or pollen
2011 Pearson Education, Inc.
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Separate populations may evolve independentlythrough mutation, natural selection, and geneticdrift
Reproductive isolation may arise as a result of
genetic divergence For example, mosquitofish in the Bahamas
comprise several isolated populations in differentponds
2011 Pearson Education, Inc.
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Sympatric (Same Country) Speciation
In sympatric speciation, speciation takes placein geographically overlapping populations
This can occur through polyploidy, habitat
differentiation, and sexual selection. (12)
2011 Pearson Education, Inc.
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Polyploidy
Polyploidy is the presence of extra sets ofchromosomes due to accidents during cell
division
Polyploidy is much more common in plants
than in animals
An autopolyploid is an individual with more
than two chromosome sets, derived from one
species
2011 Pearson Education, Inc.
Fi 24 UN01
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Figure 24.UN01Cell
division
error
2n= 6 Tetraploid cell
4n= 12
2n
2nNew species
(4n)Gametes produced
by tetraploids
(13)
Figure 24 11 4
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Figure 24.11-4
Species A
2n= 6
Species B
2n= 4
Normal
gamete
n= 3
Meiotic error;
chromosome number not
reduced from 2nto n
Unreduced gamete
with 4 chromosomes
Hybrid with7 chromosomes
Unreduced gamete
with 7 chromosomes
Normal
gameten= 3
New species:
viable fertile hybrid
(allopolyploid) 2n= 10
(14)
Allopolyploids have
more than 2 haploid
sets of chromosomes
derived from 2 different
species.
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Sexual Selection
Sexual selection can drive sympatric speciation Sexual selection for mates of different colors has
likely contributed to speciation in cichlid fish in
Lake Victoria (15)
2011 Pearson Education, Inc.
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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 naturalselection, genetic drift, or sexual selection in the
isolated populations
Even if contact is restored between populations,
interbreeding is prevented
2011 Pearson Education, Inc.
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In sympatric speciation, a reproductive barrierisolates a subset of a population without
geographic separation from the parent species
Sympatric speciation can result from polyploidy,
natural selection, or sexual selection
2011 Pearson Education, Inc.
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Concept 24.3: Hybrid zones reveal factors
that cause reproductive isolation
A hybrid zone is a region in which members of
different species mate and produce hybrids
Hybrids are the result of mating between specieswith incomplete reproductive barriers (16)
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The fossil record includes examples of species
that appear suddenly, persist essentially
unchanged for some time, and then apparentlydisappear (17)
Niles Eldredge and Stephen Jay Gould coined the
term punctuated equilibria 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
2011 Pearson Education, Inc.
Many questions remain concerning how long it
takes for new species to form, or how many genes
need to differ between species
Figure 24 17
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Figure 24.17
(a) Punctuated
pattern
Time
(b) Gradual
pattern
(18)