Transcript Speciation PPT

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 24
The Origin of Species
Lectures by
Erin Barley
Kathleen Fitzpatrick
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Video: Galápagos Tortoise
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How did this flightless bird come to live on the isolated Galápagos Islands?
Animation: Macroevolution
Right-click slide / select “Play”
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Process of species change
• Speciation, the origin of new species, is at the
focal point of evolutionary theory
Scale of evolution:
• Microevolution consists of changes in allele
frequency in a population over time
• Macroevolution refers to broad patterns of
evolutionary change above the species level
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Concept 24.1: The biological species
concept emphasizes reproductive isolation
• Biological Species Concept (one way to divide species):
– A species is a group of populations whose members can breed
and produce viable, fertile offspring
– Ability to mate = formation of a species
– Gene flow between populations holds together the phenotype of
a population (ongoing exchange of alleles)
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It’s all about ability to breed
(a) Similarity between different species
(b) Diversity within a species
Reproductive Isolation is the driving force
behind Speciation
• A new species will form when reproductive isolation occurs
– Absence of gene flow
• Reproductive Isolation:
– The existence of biological factors (barriers) that prevent two
individuals of a species from mating and producing viable and
fertile offspring
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Figure 24.3_b
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
Individuals
of
different
species
(a)
MATING
ATTEMPT
(c)
(d)
(b)
Gametic
Isolation
Mechanical
Isolation
Behavioral
Isolation
(e)
(f)
FERTILIZATION
(g)
Figure 24.3_c
Postzygotic barriers
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(h)
(i)
(j)
(k)
(l)
Limitations of the Biological Species Concept
• The biological species concept cannot be
applied 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
– HYBRIDS: For example, grizzly bears and
polar bears can mate to produce “grolar
bears”
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Figure 24.4
Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Hybrid “grolar bear”
Other Definitions of Species
1. morphological species concept:
– A species is characterized by its body shape
– It applies to sexual and asexual species but relies on
subjective criteria
2. ecological species concept:
– A species is characterized by its ecological niche
– It applies to sexual and asexual species and emphasizes
the role of disruptive selection
3. phylogenetic species concept:
– A species is the smallest group of individuals that share a
common ancestor
– It applies to sexual and asexual species, but it can be
difficult to determine the degree of difference required for
separate species
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Video: Albatross Courtship Ritual
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Video: Giraffe Courtship Ritual
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Video: Blue-footed Boobies Courtship Ritual
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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
• What do the route words mean?
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Figure 24.5
(a) Allopatric speciation.
A population forms a
new species while
geographically isolated
from its parent population.
(b) Sympatric speciation.
A subset of a population
forms a new species
without geographic
separation.
Allopatric (“Other Country”) Speciation
• In allopatric speciation, gene flow is
interrupted or reduced when a population is
divided into geographically isolated
subpopulations
– For example, the flightless cormorant of the
Galápagos likely originated from a flying
species on the mainland
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The Process of Allopatric Speciation
• The definition of barrier depends on the ability of a
population to disperse
– For example, a canyon may create a barrier for
small rodents, but not birds, coyotes, or pollen
A. harrisii
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A. leucurus
ALLOPATRIC SPECIATION
A. formosus
A. nuttingi
Atlantic Ocean
Isthmus of Panama
Pacific Ocean
A. panamensis
A. millsae
• What types of regions have the greatest
isolation?
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EXPERIMENT
Initial population
of fruit flies
(Drosophila
pseudoobscura)
Some flies raised on
maltose medium
Some flies raised
on starch medium
Mating experiments
after 40 generations
RESULTS
Female
22
9
8
20
Male
Maltose
Starch
Starch
population 1 population 2
Number of matings
in experimental group
Starch
Starch
population 2 population 1
Starch
Starch
Male
Female
Maltose
Figure 24.10
18
15
12
15
Number of matings
in control group
Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place
in geographically overlapping populations
• How can this occur if parent species is in same
area? Provide an example.
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Sympatric (“Same Country”) Speciation
• In sympatric speciation, speciation takes place
in geographically overlapping populations
• In a sympatric speciation, various factors can
limit gene flow:
– Polyploidy
– Habitat differentiation
– Sexual selection
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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.
Why do you think?
• An autopolyploid is an individual with more than two
chromosome sets, derived from one species
– When would this originate?
• An allopolyploid is a species with multiple sets of
chromosomes derived from different species (see
diagram on proceeding slides)
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Figure 24.11-1
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Figure 24.11-2
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Figure 24.11-3
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Normal
gamete
n=3
Unreduced gamete
with 7 chromosomes
Figure 24.11-4
Species A
2n = 6
Normal
gamete
n=3
Species B
2n = 4
Meiotic error;
chromosome number not
reduced from 2n to n
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Normal
gamete
n=3
Unreduced gamete
with 7 chromosomes
New species:
viable fertile hybrid
(allopolyploid) 2n = 10
• Many important crops (oats, cotton, potatoes,
tobacco, and wheat) are polyploids
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Habitat Differentiation
• Sympatric speciation can also result from the
appearance of new ecological niches
• For example, the North American maggot fly can
live on native hawthorn trees as well as more
recently introduced apple trees
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Sexual Selection: Sexual selection for mates of different colors has
likely contributed to speciation in cichlid fish in Lake Victoria
EXPERIMENT
P. pundamilia
P. nyererei
Normal light
Monochromatic
orange light
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
• Can you think of an example of where and how
this would occur?
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Patterns Within Hybrid Zones
• A hybrid zone can occur in a single band where
adjacent species meet
– For example, two species of toad in the genus
Bombina interbreed in a long and narrow hybrid
zone (see next slide)
– Would you expect hybrids to have more, less and
the same fitness as the parents?
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Figure 24.13
EUROPE
Fire-bellied
toad range
Hybrid zone
Fire-bellied toad, Bombina bombina
Yellow-bellied
toad, Bombina
variegata
Frequency of
B. variegata-specific allele
Yellow-bellied
toad range
0.99
Hybrid
zone
0.9
Yellow-bellied
toad range
0.5
Fire-bellied
toad range
0.1
0.01
40
10
0
20
10
20
30
Distance from hybrid zone center (km)
Frequency of
B. variegata-specific allele
Figure 24.13b
0.99
Hybrid
zone
0.9
Yellow-bellied
toad range
0.5
Fire-bellied
toad range
0.1
0.01
40
30
10
0
20
10
20
Distance from hybrid zone center (km)
Hybrid Zones over Time
• When closely related species meet in a hybrid
zone, there are three possible outcomes:
– Reinforcement
– Fusion
– Stability
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Figure 24.14-1
Gene flow
Population
Barrier to
gene flow
Formation of a hybrid zone and possible outcomes for hybrids over time.
Isolated
population
diverges
Gene flow
Population
Barrier to
gene flow
Figure 24.14-3
Isolated
population
diverges
Hybrid
zone
Gene flow
Population
Barrier to
gene flow
Hybrid
individual
Figure 24.14-4
Possible
outcomes:
Isolated
population
diverges
Hybrid
zone
Reinforcement
OR
Fusion
OR
Gene flow
Population
Barrier to
gene flow
Hybrid
individual
Stability
Reinforcement: Strengthening Reproductive
Barriers
• The reinforcement of barriers occurs when
hybrids are less fit than the parent species
• Over time, the rate of hybridization decreases
• Where reinforcement occurs, reproductive barriers
should be stronger for sympatric than allopatric
species
– For example, in populations of flycatchers, males
are more similar in allopatric populations than
sympatric populations
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Figure 24.15
Females choosing between
these males:
28
Number of females
24
Females choosing between
these males:
Sympatric pied male
Allopatric pied male
Sympatric collared male
Allopatric collared male
20
16
12
8
4
(none)
0
Own
species
Other
species
Female mate choice
Own
species
Other
species
Female mate choice
Fusion: Weakening Reproductive Barriers
• If hybrids are as fit as parents, there can be
substantial gene flow between species
– How would increasing gene flow affect separate
species?
• For example, researchers think that pollution
in Lake Victoria has reduced the ability of
female cichlids to distinguish males of
different species
– How would this affect different cichlid species?
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Figure 24.16
Pundamilia nyererei
Pundamilia pundamilia
Pundamilia “turbid water,”
hybrid offspring from a location
with turbid water
Concept 24.4: Speciation can occur rapidly
or slowly and can result from changes in
few or many genes
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The Time Course of Speciation
• By what tools can we determine rate of
speciation?
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The Time Course of Speciation
• By what tools can we determine rate of
speciation?
– fossil record,
– morphological data, or
– molecular data
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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 equilibria to describe periods of
apparent stasis punctuated by sudden change
– Compare punctuated equlibrium to uniformitarianism.
– Which model is more correct?
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Figure 24.17
(a) Punctuated
pattern
Time
(b) Gradual
pattern
Represent these two models in
graphic form
Speciation Rates
• The punctuated pattern in the fossil record and
evidence from lab studies suggest that speciation
can be rapid
– For example, the sunflower Helianthus anomalus
originated from the hybridization of two other
sunflower species
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Figure 24.18
EXPERIMENT
H. annuus
gamete
H. petiolarus
gamete
How does hybridization lead to
speciation in sunflowers??
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
RESULTS
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
Average rates of speciation
• The interval between speciation events can range
from 4,000 years (some cichlids) to 40 million
years (some beetles), with an average of 6.5
million years
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Studying the Genetics of Speciation
• A fundamental question of evolutionary biology
persists: How many genes change when a new
species forms?
For example:
• In Japanese Euhadra snails, the direction of
shell spiral affects mating and is controlled by a
single gene
• In monkey flowers (Mimulus), two loci affect flower
color, which influences pollinator preference
– Pollination that is dominated by either hummingbirds
or bees can lead to reproductive isolation of the
flowers
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Figure 24.20
(a) Typical
Mimulus
lewisii
(b) M. lewisii with an
M. cardinalis flower-color
allele
(c) Typical
Mimulus
cardinalis
(d) M. cardinalis with an
M. lewisii flower-color
allele
VOCAB REVIEW
• The cumulative effect of many
speciation and extinction events is
called ________________ .
• The ____________species concept
defines a species by structural features.
• The sudden change in a species after a
long period of no change is called
____________.
Figure 24.UN01
Cell
division
error
The new
species would
be called a
___________.
2n = 6
4n = 12
2n
2n
Gametes produced
New species
(4n)
Figure 24.UN02
Fill in the
blanks
Original population
_______ speciation
________ speciation
Answers to VOCAB REVIEW
•
•
•
•
•
•
Macroevolution
Morphological
Punctuated equlibrium
Polyploid, or tetraploid more specifically
Allopatric
Sympatric
TRY…Test Your Understanding,
question 10
Figure 24.UN03
Ancestral species:
Triticum
monococcum
(2n = 14)
Test Your Understanding, question 10
Wild
Triticum
(2n = 14)
Product:
T. aestivum
(bread wheat)
(2n = 42)
Wild
T. tauschii
(2n = 14)
Figure 24.UN04