Download AP Biology Big Idea 1 part C

Big Idea #1 Part C
Evolution Continues in a
Changing Environment
1. Speciation and Extinction
(Rates/adaptive radiation)
2. Role of Reproductive Isolation
3. Populations continue to evolve
The Biological Species
Concept
 The biological species concept states that
a species 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
 Gene flow between populations holds the
phenotype of a population together
© 2011 Pearson Education, Inc.
Figure 24.2
(a) Similarity between different species
(b) Diversity within a species
Reproductive Isolation
 Reproductive isolation is the existence of
biological 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
© 2011 Pearson Education, Inc.
Figure 24.3_a
Prezygotic barriers
Habitat
Isolation
Temporal
Isolation
(a)
Gametic
Isolation
Mechanical
Isolation
Behavioral
Isolation
Individuals
of
different
species
Postzygotic barriers
MATING
ATTEMPT
(c)
(d)
(e)
Reduced Hybrid
Viability
Reduced Hybrid
Fertility
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(f)
(g)
(h)
(i)
(j)
(b)
(k)
(l)
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)
 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.
Figure 24.3a
Figure 24.3b
 Habitat isolation: Two species
encounter each other rarely, or not
at all, because they occupy
different habitats, even though not
isolated by physical barriers
© 2011 Pearson Education, Inc.
Figure 24.3c
 Temporal isolation: Species that
breed at different times of the day,
different seasons, or different years
cannot mix their gametes
© 2011 Pearson Education, Inc.
Figure 24.3e
(e)
 Behavioral isolation: Courtship
rituals and other behaviors unique
to a species are effective barriers
Video: Albatross Courtship Ritual
Video: Giraffe Courtship Ritual
Video: Blue-footed Boobies Courtship Ritual
© 2011 Pearson Education, Inc.
Figure 24.3f
(f)
 Mechanical isolation: Morphological
differences can prevent successful
mating
© 2011 Pearson Education, Inc.
Figure 24.3g
(g)
 Gametic Isolation: Sperm of one
species may not be able to fertilize
eggs of another species
© 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
© 2011 Pearson Education, Inc.
Figure 24.3h
(h)
 Reduced hybrid viability: Genes
of the different parent species may
interact and impair the hybrid’s
development
© 2011 Pearson Education, Inc.
Figure 24.3i
(i)
 Reduced hybrid fertility: Even
if hybrids are vigorous, they
may be sterile
© 2011 Pearson Education, Inc.
Figure 24.3l
(l)
 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
© 2011 Pearson Education, Inc.
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
 For example, grizzly bears and polar bears
can mate to produce “grolar bears”
© 2011 Pearson Education, Inc.
Figure 24.4
Grizzly bear (U. arctos)
Polar bear (U. maritimus)
Hybrid “grolar bear”
Other Definitions of Species
 Other species concepts emphasize the unity within
a species rather than the separateness of different
species
 The morphological species concept
defines a species by structural features
 It applies to sexual and asexual species
but relies on subjective criteria
© 2011 Pearson Education, Inc.
 The ecological species concept views a
species in terms of its ecological niche
 It applies to sexual and asexual species and
emphasizes the role of disruptive selection
 The phylogenetic species concept defines
a species as the smallest group of
individuals on a phylogenetic tree
 It applies to sexual and asexual species, but it
can be difficult to determine the degree of
difference required for separate species
© 2011 Pearson Education, Inc.
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.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 24.6
A. harrisii
A. leucurus
 Separate populations may evolve
independently through mutation,
natural selection, and genetic drift
 Reproductive isolation may arise as a
result of genetic divergence
 For example, mosquitofish in the
Bahamas comprise several isolated
populations in different ponds
© 2011 Pearson Education, Inc.
Figure 24.7
(a) Under high predation
(b) Under low predation
Evidence of Allopatric
Speciation
 15 pairs of sibling species of snapping
shrimp (Alpheus) are separated by the
Isthmus of Panama
 These species originated 9 to 13 million
years ago, when the Isthmus of Panama
formed and separated the Atlantic and
Pacific waters
© 2011 Pearson Education, Inc.
Figure 24.8
A. formosus
A. nuttingi
Atlantic Ocean
Isthmus of Panama
Pacific Ocean
A. panamensis
A. millsae
 Regions with many geographic
barriers typically have more
species than do regions with fewer
barriers
 Reproductive isolation between
populations generally increases as
the distance between them
increases
 For example, reproductive isolation
increases between dusky
salamanders that live further apart
© 2011 Pearson Education, Inc.
Degree of reproductive isolation
Figure 24.9
Barriers to reproduction are intrinsic;
separation itself is not a biological barrier
2.0
1.5
1.0
0.5
0
0
50 100
150
200
250
300
Geographic distance (km)
Figure 24.10 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
9
8
20
Male
22
Starch
Starch
population 1 population 2
Number of matings
in experimental group
Starch
Starch
population 2 population 1
Maltose
Starch
Male
Starch
Maltose
Female
18
15
12
15
Number of matings
in control group
Figure 24.10b
RESULTS
Female
Maltose
22
9
8
20
Number of matings
in experimental group
Starch
Starch
population 2 population 1
Starch
Starch
Starch
population 1 population 2
Male
Male
Maltose
Starch
Female
18
15
12
15
Number of matings
in control group
Sympatric (“Same Country”)
Speciation
 In sympatric speciation, speciation takes
place in geographically overlapping
populations
© 2011 Pearson Education, Inc.
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
 An autopolyploid is an individual with
more than two chromosome sets,
derived from one species
© 2011 Pearson Education, Inc.
 An allopolyploid is a species with
multiple sets of chromosomes derived
from different species
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 24.12
EXPERIMENT
Normal light
P. pundamilia
P. nyererei
Monochromatic
orange light
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
© 2011 Pearson Education, Inc.
 In sympatric speciation, a
reproductive barrier isolates 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.
Concept 24.3: Hybrid zones
provide opportunities to study
factors that cause reproductive
isolation
A hybrid zone is a region in
which members of different
species mate and produce
hybrids
Patterns Within Hybrid Zones
 A hybrid zone can occur in a single
band where adjacent species meet
 Hybrids often have reduced fitness
compared with parent species
 The distribution of hybrid zones can be
more complex if parent species are
found in multiple habitats within the
same region
Fig. 24-13
EUROPE
Fire-bellied
toad range
Hybrid zone
0.99
Allele frequency (log scale)
Yellow-bellied toad,
Bombina variegata
Yellow-bellied
toad range
Fire-bellied toad,
Bombina bombina
0.9
0.5
0.1
0.01
40
20
30
10
0
10
20
Distance from hybrid zone center (km)
Fig. 24-13a
Yellow-bellied toad,
Bombina variegata
Fig. 24-13b
Fire-bellied toad,
Bombina bombina
Fig. 24-13c
Fire-bellied
toad range
Hybrid zone
Allele frequency (log scale)
Yellow-bellied
toad range
0.99
0.9
0.5
0.1
0.01
40
20
10
0
30
20
10
Distance from hybrid zone center (km)
Hybrid Zones over Time
When closely related species meet in a hybrid
zone, there are three possible outcomes:
Strengthening of reproductive
barriers
Weakening of reproductive
barriers
Continued formation of hybrid
individuals
Fig. 24-14-1
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
Fig. 24-14-2
Isolated population
diverges
Gene flow
Population
(five individuals
are shown)
Barrier to
gene flow
Fig. 24-14-3
Isolated population
diverges
Hybrid
zone
Gene flow
Hybrid
Population
(five individuals
are shown)
Barrier to
gene flow
Fig. 24-14-4
Isolated population
diverges
Possible
outcomes:
Hybrid
zone
Reinforcement
OR
Fusion
Gene flow
Hybrid
Population
(five individuals
are shown)
OR
Barrier to
gene flow
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
Fig. 24-15
Sympatric male
pied flycatcher
28
Allopatric male
pied flycatcher
Pied flycatchers
24
Number of females
Collared flycatchers
20
16
12
8
4
(none)
0
Females mating Own
Other
with males from: species species
Sympatric males
Own
Other
species species
Allopatric males
Fig. 24-15a
Sympatric male
pied flycatcher
Allopatric male
pied flycatcher
Fig. 24-15b
28
Pied flycatchers
24
Number of females
Collared flycatchers
20
16
12
8
4
(none)
0
Other
Females mating Own
with males from: species species
Sympatric males
Own
Other
species species
Allopatric males
Fusion: Weakening
Reproductive Barriers
 If hybrids are as fit as parents, there
can be substantial gene flow
between species
 If gene flow is great enough, the
parent species can fuse into a single
species
Fig. 24-16
Pundamilia nyererei
Pundamilia pundamilia
Pundamilia “turbid water,”
hybrid offspring from a location
with turbid water
Stability: Continued Formation
of Hybrid Individuals
 Extensive gene flow from outside the hybrid
zone can overwhelm selection for increased
reproductive isolation inside the hybrid zone
 In cases where hybrids have increased
fitness, local extinctions of parent species
within the hybrid zone can prevent the
breakdown of reproductive barriers
Concept 24.4: Speciation can
occur rapidly or slowly and can
result from changes in few or
many genes
Many questions remain concerning how
long it takes for new species to form, or
how many genes need to differ
between species
The Time Course of Speciation
Broad patterns in speciation can
be studied using the fossil
record, morphological data, or
molecular data
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
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
Fig. 24-18
(a) The wild sunflower Helianthus anomalus
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
H. anomalus
Chromosome 3
Experimental hybrid
Key
Region diagnostic for
parent species H. petiolaris
Region diagnostic for
parent species H. annuus
Region lacking information on parental origin
(b) The genetic composition of three chromosomes in H.
anomalus and in experimental hybrids
Fig. 24-18a
(a) The wild sunflower Helianthus anomalus
Fig. 24-18b
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
H. anomalus
Chromosome 3
Experimental hybrid
Key
Region diagnostic for
parent species H. petiolaris
Region diagnostic for
parent species H. annuus
Region lacking information on parental origin
(b) The genetic composition of three chromosomes in H.
anomalus and in experimental hybrids
Studying the Genetics of
Speciation
 The explosion of genomics is
enabling researchers to identify
specific genes involved in some
cases of speciation
 Depending on the species in
question, speciation might require
the change of only a single allele or
many alleles
Fig. 24-19
Fig. 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
From Speciation to
Macroevolution
 Macroevolution is the cumulative
effect of many speciation and
extinction events
Fig. 24-UN1
Original population
Allopatric speciation
Sympatric speciation
Fig. 24-UN2
Ancestral species:
AA
Triticum
monococcum
(2n = 14)
BB
Wild
Triticum
(2n = 14)
Product:
AA BB DD
T. aestivum
(bread wheat)
(2n = 42)
DD
Wild
T. tauschii
(2n = 14)
Fig. 24-UN3
You should now be able to:
1. Define and discuss the limitations of the four
species concepts
2. Describe and provide examples of prezygotic
and postzygotic reproductive barriers
3. Distinguish between and provide examples of
allopatric and sympatric speciation
4. Explain how polyploidy can cause
reproductive isolation
5. Define the term hybrid zone and describe
three outcomes for hybrid zones over time
Concept 25.4: The rise and fall of
dominant groups reflect continental
drift, mass extinctions, and adaptive
radiations
 The history of life on Earth has seen the rise
and fall of many groups of organisms
Video: Volcanic Eruption
Video: Lava Flow
Continental Drift
 At three points in time, the land masses of
Earth have formed a supercontinent: 1.1 billion,
600 million, and 250 million years ago
 Earth’s continents move slowly over the
underlying hot mantle through the process of
continental drift
 Oceanic and continental plates can collide,
separate, or slide past each other
 Interactions between plates cause the
formation of mountains and islands, and
earthquakes
Fig. 25-12
North
American
Plate
Crust
Juan de Fuca
Plate
Eurasian Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Mantle
Pacific
Plate
Outer
core
Inner
core
(a) Cutaway view of Earth
Indian
Plate
Cocos Plate
Nazca
Plate
South
American
Plate
African
Plate
Scotia Plate
(b) Major continental plates
Antarctic
Plate
Australian
Plate
Fig. 25-12a
Crust
Mantle
Outer
core
Inner
core
(a) Cutaway view of Earth
Fig. 25-12b
North
American
Plate
Juan de Fuca
Plate
Eurasian Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Scotia Plate
(b) Major continental plates
African
Plate
Antarctic
Plate
Australian
Plate
Consequences of Continental Drift
 Formation of the supercontinent Pangaea
about 250 million years ago had many
effects
 A reduction in shallow water habitat
 A colder and drier climate inland
 Changes in climate as continents moved
toward and away from the poles
 Changes in ocean circulation patterns
leading to global cooling
Fig. 25-13
Cenozoic
Present
Eurasia
Africa
65.5
South
America
India
Madagascar
251
Mesozoic
135
Paleozoic
Millions of years ago
Antarctica
Fig. 25-13a
Cenozoic
Millions of years ago
Present
65.5
Eurasia
Africa
South
America
India
Madagascar
Antarctica
251
Mesozoic
135
Paleozoic
Millions of years ago
Fig. 25-13b
 The break-up of Pangaea lead to
allopatric speciation
 The current distribution of fossils reflects
the movement of continental drift
 For example, the similarity of fossils in
parts of South America and Africa is
consistent with the idea that these
continents were formerly attached
Mass Extinctions
 The fossil record shows that most
species that have ever lived are now
extinct
 At times, the rate of extinction has
increased dramatically and caused a
mass extinction
The “Big Five” Mass Extinction
Events
 In each of the five mass extinction events,
more than 50% of Earth’s species became
extinct
Fig. 25-14
800
700
15
600
500
10
400
300
5
200
100
0
Era
Period
542
E
O
Paleozoic
S
D
488 444 416
359
C
Tr
P
299
251
Mesozoic
C
J
200
145
Time (millions of years ago)
Cenozoic
P
65.5
N
0
0
Number of families:
Total extinction rate
(families per million years):
20
 The Permian extinction defines the boundary
between the Paleozoic and Mesozoic eras
 This mass extinction occurred in less than 5
million years and caused the extinction of
about 96% of marine animal species
 This event might have been caused by
volcanism, which lead to global warming, and a
decrease in oceanic oxygen
 The Cretaceous mass extinction 65.5 million
years ago separates the Mesozoic from the
Cenozoic
 Organisms that went extinct include about half
of all marine species and many terrestrial
plants and animals, including most dinosaurs
Fig. 25-15
NORTH
AMERICA
Yucatán
Peninsula
Chicxulub
crater
 The presence of iridium in
sedimentary rocks suggests a
meteorite impact about 65 million
years ago
 The Chicxulub crater off the
coast of Mexico is evidence of a
meteorite that dates to the same
time
Is a Sixth Mass Extinction Under
Way?
 Scientists estimate that the current rate of
extinction is 100 to 1,000 times the typical
background rate
 Data suggest that a sixth human-caused mass
extinction is likely to occur unless dramatic
action is taken
Consequences of Mass
Extinctions
 Mass extinction can alter ecological
communities and the niches available to
organisms
 It can take from 5 to 100 million years for
diversity to recover following a mass extinction
 Mass extinction can pave the way for adaptive
radiations
Predator genera
(percentage of marine genera)
Fig. 25-16
50
40
30
20
10
0
Paleozoic
Mesozoic
Era
D
C
P
C
E
O S
J
Tr
Period
359
488 444 416
542
299 251
200
145
Time (millions of years ago)
Cenozoic
P
65.5
N
0
Adaptive Radiations
 Adaptive radiation is the evolution of diversely
adapted species from a common ancestor
upon introduction to new environmental
opportunities
Worldwide Adaptive Radiations
 Mammals underwent an adaptive radiation
after the extinction of terrestrial dinosaurs
 The disappearance of dinosaurs (except birds)
allowed for the expansion of mammals in
diversity and size
 Other notable radiations include photosynthetic
prokaryotes, large predators in the Cambrian,
land plants, insects, and tetrapods
Fig. 25-17
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324 species)
Eutherians
(placental
mammals;
5,010 species)
250
200
100
150
Millions of years ago
50
0
Regional Adaptive Radiations
 Adaptive radiations can occur when organisms
colonize new environments with little
competition
 The Hawaiian Islands are one of the world’s
great showcases of adaptive radiation
Fig. 25-18
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7 LANAI
million
years
1.3
MAUI million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Fig. 25-18a
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7
million
years
1.3
MAUI million
years
LANAI
HAWAII
0.4
million
years
Fig. 25-18b
Close North American relative,
the tarweed Carlquistia muirii
Fig. 25-18c
Dubautia waialealae
Fig. 25-18d
Dubautia laxa
Fig. 25-18e
Dubautia scabra
Fig. 25-18f
Argyroxiphium sandwicense
Fig. 25-18g
Dubautia linearis