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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
© 2011 Pearson Education, Inc.
Overview: That “Mystery
y
y of Mysteries”
y
• In the Galápagos Islands Darwin discovered
plants
l t and
d animals
i l ffound
d nowhere
h
else
l on E
Earth
th
© 2011 Pearson Education, Inc.
Video: Galápagos Tortoise
© 2011 Pearson Education, Inc.
Figure 24.1
• Speciation, the origin of new species, is at the
focal point of evolutionary theory
• Evolutionary theory must explain how new species
originate and how populations evolve
• Microevolution consists of changes in allele
frequencyy in a population over time
• Macroevolution refers to broad patterns of
evolutionary change above the species level
© 2011 Pearson Education, Inc.
Animation: Macroevolution
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
Concept
p 24.1: The biological
g
species
p
concept emphasizes reproductive isolation
• Species is a Latin word meaning “kind” or
“appearance”
• Biologists compare morphology, physiology,
biochemistry, and DNA sequences when
grouping organisms
© 2011 Pearson Education, Inc.
The Biological
g
Species
p
Concept
p
• The biological species concept states that a
species
i is
i a group off populations
l ti
whose
h
members
b
have the potential to interbreed in nature and
produce viable
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
Figure 24.2a
(a) Similarity between different species
Figure 24.2b
(b) Diversity within a species
Figure 24.2c
Figure 24.2d
Figure 24.2e
Figure 24.2f
Figure 24.2g
Figure 24.2h
Figure 24.2i
Figure 24.2j
Reproductive
p
Isolation
• Reproductive isolation is the existence of
bi l i l ffactors
biological
t
(b
(barriers)
i ) th
thatt iimpede
d ttwo
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
IIsolation
l ti
Mechanical
I l i
Isolation
Behavioral
Isolation
Individuals
of
different
species
Postzygotic barriers
MATING
ATTEMPT
(c)
(d)
(e)
Reduced Hybrid
Vi bilit
Viability
Reduced Hybrid
F tilit
Fertility
Hybrid
Breakdown
B
kd
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
y
Reduced Hybrid
Fertility
y
Hybrid
Breakdown
VIABLE,
FERTILE
OFFSPRING
FERTILIZATION
(h)
(i)
(j)
(k)
(l)
• Prezygotic barriers block fertilization from
occurring
i b
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
( )
(a)
Figure 24.3b
(b)
• Habitat isolation: Two species encounter each
other
th rarely,
l or nott att all,
ll b
because th
they occupy
different habitats, even though not isolated by
physical barriers
© 2011 Pearson Education, Inc.
Figure 24.3c
(c)
Figure 24.3d
(d)
• Temporal isolation: Species that breed at
diff
different
t ti
times off the
th day,
d
diff
differentt seasons,
or different years cannot mix their gametes
© 2011 Pearson Education, Inc.
Figure 24.3e
(e)
• Behavioral isolation: Courtship rituals and other
b h i
behaviors
unique
i
tto a species
i are effective
ff ti
barriers
© 2011 Pearson Education, Inc.
Video: Albatross Courtship Ritual
© 2011 Pearson Education, Inc.
Video: Giraffe Courtship Ritual
© 2011 Pearson Education, Inc.
Video: Blue-footed Boobies Courtship Ritual
© 2011 Pearson Education, Inc.
Figure 24.3f
(f)
• Mechanical isolation: Morphological differences
can preventt successful
f l mating
ti
© 2011 Pearson Education, Inc.
Figure 24.3g
(g)
• Gametic Isolation: Sperm of one species may not
b able
be
bl tto ffertilize
tili eggs off another
th species
i
© 2011 Pearson Education, Inc.
• Postzygotic barriers prevent the hybrid zygote
f
from
developing
d
l i iinto
t a viable,
i bl ffertile
til adult:
d lt
– Reduced hybrid viability
– Reduced
R d
dh
hybrid
b id ffertility
tilit
– Hybrid breakdown
© 2011 Pearson Education, Inc.
Figure 24.3h
(h)
• Reduced hybrid viability: Genes of the different
parentt species
i may iinteract
t
t and
d impair
i
i th
the
hybrid’s development
© 2011 Pearson Education, Inc.
Figure 24.3i
(i)
Figure 24.3j
(j)
Figure 24.3k
(k)
• Reduced hybrid fertility: Even if hybrids are
vigorous,
i
th
they may b
be sterile
t il
© 2011 Pearson Education, Inc.
Figure 24.3l
(l)
• Hybrid breakdown: Some first-generation hybrids
are fertile,
f til b
butt when
h th
they mate
t with
ith another
th
species or with either parent species, offspring of
the next generation are feeble or sterile
© 2011 Pearson Education, Inc.
Limitations off the Biological
g
Species
p
Concept
p
• The biological species concept cannot be
applied
li d tto ffossils
il or asexuall organisms
i
(including all prokaryotes)
• The biological species concept emphasizes
absence of gene flow
• However,
However gene flow can occur between
distinct species
– For example,
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”
Figure 24.4a
Grizzly bear (U
(U. arctos)
Figure 24.4b
Polar bear (U. maritimus)
Figure 24.4c
Hybrid “grolar bear”
Other Definitions of Species
p
• Other species concepts emphasize the unity within
a species
i rather
th th
than th
the separateness
t
off different
diff
t
species
• The
Th morphological
h l i l species
i conceptt defines
d fi
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
i tterms off its
in
it ecological
l i l niche
i h
– 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
p 24.2: Speciation
p
can take p
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
p
((“Other Country”)
y ) Speciation
p
• In allopatric speciation, gene flow is
i t
interrupted
t d or reduced
d
d when
h a population
l ti iis
divided into geographically isolated
subpopulations
– For example, the flightless cormorant of the
Galápagos
p g likely
y originated
g
from a flying
y g
species on the mainland
© 2011 Pearson Education, Inc.
The Process off Allopatric
p
Speciation
p
• The definition of barrier depends on the ability of a
population
l ti tto di
disperse
– For example, a canyon may create a barrier for
small rodents
rodents, but not birds,
birds coyotes,
coyotes or pollen
© 2011 Pearson Education, Inc.
Figure 24.6
A. harrisii
A. leucurus
Figure 24.6a
A. harrisii
Figure 24.6b
A. leucurus
Figure 24.6c
• Separate populations may evolve independently
through mutation
mutation, natural selection
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
Figure 24.7a
Figure 24.7b
Evidence off Allopatric
p
Speciation
p
• 15 pairs of sibling species of snapping shrimp
(Al h
(Alpheus)
) are separated
t d by
b th
the IIsthmus
th
off
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
Figure 24.8a
Figure 24.8b
Atlantic Ocean
Isthmus of Panama
Pacific Ocean
Figure 24.8c
A formos
A.
formosus
s
Figure 24.8d
A. panamensis
p
Figure 24.8e
A nuttingi
A.
tti i
Figure 24.8f
A millsae
A.
• 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 o
of reprod
ductive isolation
Figure 24.9
2.0
1.5
1.0
0.5
0
0
50
100
150
200
250
Geographic distance (km)
300
• Barriers to reproduction are intrinsic;
separation
ti it
itself
lf iis nott a bi
biological
l i lb
barrier
i
© 2011 Pearson Education, Inc.
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
S
po
opulation 2 pop
pulation 1
Starch
Starch
S
Male
Female
Maltose
M
Figure 24.10
18
15
12
15
Number of matings
in control group
Figure 24.10a
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
Figure 24.10b
RESULTS
Female
Maltose
22
9
8
20
Number of matings
in experimental group
Starch
Starc
ch
population 2 populattion 1
Starch
Starch
Starch
population 1 population 2
Male
M
M
Male
Maltose
M
Starrch
Female
18
15
12
15
Number of matings
in control group
Sympatric
y p
((“Same Country”)
y ) Speciation
p
• In sympatric speciation, speciation takes place
i geographically
in
hi ll overlapping
l
i populations
l ti
© 2011 Pearson Education, Inc.
Polyploidy
yp
y
• Polyploidy is the presence of extra sets of
chromosomes
h
d
due tto accidents
id t d
during
i cellll
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
t off chromosomes
h
derived
d i d ffrom diff
differentt
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,
t b
tobacco,
and
d wheat)
h t) are polyploids
l l id
© 2011 Pearson Education, Inc.
Habitat Differentiation
ff
• Sympatric speciation can also result from the
appearance off new ecological
l i l niches
i h
• 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
P. nyererei
Monochromatic
orange light
Figure 24.12a
Normal light
P. pundamilia
Figure 24.12b
Normal light
P. nyererei
Figure 24.12c
Monochromatic
orange light
P. pundamilia
Figure 24.12d
Monochromatic
orange light
P. nyererei
Allopatric
p
and Sympatric
y p
Speciation:
p
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
i l t a subset
isolates
b t off a population
l ti without
ith t
geographic separation from the parent species
• Sympatric
S mpatric speciation can result
res lt from pol
polyploidy,
ploid
natural selection, or sexual selection
© 2011 Pearson Education, Inc.
Concept
p 24.3: Hybrid
y
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 species
with incomplete reproductive barriers
© 2011 Pearson Education, Inc.
Patterns Within Hybrid
y
Zones
• A hybrid zone can occur in a single band where
adjacent
dj
t species
i meett
– For example, two species of toad in the genus
Bombina interbreed in a long and narrow hybrid
zone
© 2011 Pearson Education, Inc.
Figure 24.13
EUROPE
Fire-bellied
toad range
Hybrid zone
Fire-bellied toad, Bombina bombina
Yellow-bellied
toad Bombina
toad,
variegata
Frequency of
B. variega
ata-specific allele
Yellow-bellied
toad range
0.99
Hybrid
zone
0.9
Yellow-bellied
toad range
g
0.5
Fire-bellied
toad range
g
0.1
0.01
40
10
0
20
10
20
30
Distance from hybrid zone center (km)
Figure 24.13a
EUROPE
Fire-bellied
toad range
Hybrid zone
Yellow-bellied
toad range
Frequency of
B. variiegata-s
specific allele
Figure 24.13b
0.99
Hybrid
zone
0.9
Yellow-bellied
Yellow
bellied
toad range
0
0.5
Fire-bellied
Fire
bellied
toad range
01
0.1
0.01
40
30
10
0
20
10
20
Distance from hybrid zone center (km)
Figure 24.13c
Fire-bellied toad, Bombina bombina
Figure 24.13d
Yellow-bellied toad, Bombina variegata
• Hybrids often have reduced fitness compared with
parentt species
i
• The distribution of hybrid zones can be more
comple if parent species are fo
complex
found
nd in patches
within the same region
© 2011 Pearson Education, Inc.
Hybrid
y
Zones over Time
• When closely related species meet in a hybrid
zone, there
th
are th
three possible
ibl outcomes:
t
– Reinforcement
– Fusion
F i
– Stability
© 2011 Pearson Education, Inc.
Figure 24.14-1
Gene flow
Population
Barrier to
gene flow
Figure 24.14-2
Isolated
population
diverges
Gene flow
Population
Barrier to
gene flow
Figure 24.14-3
Isolated
population
diverges
Gene flow
Population
Barrier to
gene flow
Hybrid
zone
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:
f
Strengthening
g
g Reproductive
p
Barriers
• The reinforcement of barriers occurs when
hybrids are less fit than the parent species
• Over
O
time,
ti
the
th rate
t off hybridization
h b idi ti d
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
© 2011 Pearson Education, Inc.
Figure 24.15
Females choosing between
these males:
28
Nu
umber of fe
emales
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
p
species
Other
species
p
Female mate choice
Own
species
Other
p
species
Female mate choice
Fusion: Weakeningg Reproductive
p
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
• For example, researchers think that pollution
in Lake Victoria has reduced the abilityy of
female cichlids to distinguish males of
different species
• This
Thi might
i ht be
b causing
i th
the ffusion
i off many
species
© 2011 Pearson Education, Inc.
Figure 24.16
Pundamilia nyererei
Pundamilia pundamilia
Pundamilia
P
d ili “turbid
“t bid water,”
t ”
hybrid offspring from a location
with turbid water
Figure 24.16a
Pundamilia nyererei
Figure 24.16b
Pundamilia pundamilia
Figure 24.16c
Pundamilia “turbid water,” hybrid offspring from a
location with turbid water
Stability:
y Continued Formation off Hybrid
y
Individuals
• Extensive gene flow from outside the hybrid zone
can overwhelm selection for increased
reproductive
d ti iisolation
l ti iinside
id th
the h
hybrid
b id zone
© 2011 Pearson Education, Inc.
Concept
p 24.4: Speciation
p
can occur rapidly
p y
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
© 2011 Pearson Education, Inc.
The Time Course of Speciation
p
• Broad patterns in speciation can be studied
using
i th
the ffossilil record,
d morphological
h l i ld
data,
t or
molecular data
© 2011 Pearson Education, Inc.
Patterns in the Fossil Record
• The fossil record includes examples of species
th t appear suddenly,
that
dd l persist
i t essentially
ti ll
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
• The punctuated equilibrium model contrasts with a
model of gradual change in a species’ existence
© 2011 Pearson Education, Inc.
Figure 24.17
(a) Punctuated
pattern
Time
(b) Gradual
pattern
Speciation
p
Rates
• The punctuated pattern in the fossil record and
evidence
id
ffrom llab
b studies
t di suggestt th
thatt speciation
i ti
can be rapid
– For example,
example the sunflower Helianthus anomalus
originated from the hybridization of two other
sunflower species
p
© 2011 Pearson Education, Inc.
Figure 24.18
Figure 24.19
EXPERIMENT
H. annuus
gamete
H. petiolarus
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes are shown)
RESULTS
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
Figure 24.19a
EXPERIMENT
H. annuus
H
gamete
H. petiolarus
H
gamete
F1 experimental hybrid
(4 of the 2n = 34
chromosomes
h
are shown)
h
)
Figure 24.19b
RESULTS
H. anomalus
Chromosome 1
Experimental hybrid
H. anomalus
Chromosome 2
Experimental hybrid
• The interval between speciation events can range
f
from
4,000
4 000 years ((some cichlids)
i hlid ) tto 40 million
illi
years (some beetles), with an average of 6.5
million years
© 2011 Pearson Education, Inc.
Studying
y g the Genetics of Speciation
p
• A fundamental question of evolutionary biology
persists:
i t How
H
many genes change
h
when
h a new
species forms?
• Depending
D
di on th
the species
i iin question,
ti
speciation
i ti
might require the change of only a single allele or
many alleles
– For example, in Japanese Euhadra snails, the
direction of shell spiral
p
affects mating
g and is
controlled by a single gene
© 2011 Pearson Education, Inc.
• In monkey flowers (Mimulus), two loci affect flower
color,
l which
hi h iinfluences
fl
pollinator
lli t preference
f
• Pollination that is dominated by either
h
hummingbirds
i bi d or b
bees can llead
d tto reproductive
d ti
isolation of the flowers
• In other species
species, speciation can be influenced by
larger numbers of genes and gene interactions
© 2011 Pearson Education, Inc.
Figure 24.20
( ) Typical
(a)
T i l
Mimulus
lewisii
M lewisii with an
(b) M.
M. cardinalis flower-color
allele
(c) Typical
Mimulus
cardinalis
(d) M.
M cardinalis with an
M. lewisii flower-color
allele
Figure 24.20a
( ) Typical
(a)
T i l Mimulus
Mi l lewisii
l i ii
Figure 24.20b
(b) M. lewisii with an
M cardinalis
M.
di li flower-color
fl
l
allele
Figure 24.20c
(c) Typical Mimulus cardinalis
Figure 24.20d
(d) M. cardinalis with an
M lewisii flower-color
M.
allele
From Speciation
p
to Macroevolution
• Macroevolution is the cumulative effect of many
speciation
i ti and
d extinction
ti ti events
t
© 2011 Pearson Education, Inc.
Figure 24.UN01
Cell
division
error
2 =6
2n
Tetraploid
T
t
l id cell
ll
4n = 12
2n
2n
Gametes produced
by tetraploids
New species
(4n)
Figure 24.UN02
Original population
Allopatric speciation
Sympatric speciation
Figure 24.UN03
Ancestral species:
Triticum
monococcum
(2n = 14)
Wild
Triticum
(2n = 14)
Product:
T. aestivum
((bread wheat))
(2n = 42)
Wild
T. tauschii
(2n = 14)
Figure 24.UN04