Speciation and
Macroevolution
Chapter 20
Learning Objective 1
•
What is the biological species concept?
•
List two potential problems with the
concept
Biological Species Concept
•
Species
•
•
•
•
one or more populations
members interbreed in nature
produce fertile offspring
do not interbreed with different species
Sterile Hybrid
Problems
•
Biological species concept applies only to
sexually reproducing organisms
•
Individuals assigned to different species
may occasionally successfully interbreed
KEY CONCEPTS
•
According to the biological species
concept, a species consists of individuals
that can successfully interbreed with one
another but not with individuals from other
species
Learning Objective 2
•
What is the significance of reproductive
isolating mechanisms?
•
Distinguish among different prezygotic and
postzygotic barriers
Reproductive Isolating Mechanisms
•
Restrict gene flow between species
•
Prezygotic barriers
•
•
prevent fertilization from taking place
Postzygotic barriers
•
prevent gene flow after fertilization has taken
place (reproductive isolating mechanisms)
Prezygotic Barriers (1)
•
Temporal isolation
•
•
two species reproduce at different times of
day, season, or year
Habitat isolation
•
two closely related species live and breed in
different habitats in same geographic area
Temporal Isolation
Fig. 20-2a, p. 430
Fig. 20-2b, p. 430
Leopard
frog
Mating activity
Wood
frog
March 1
April 1
May 1
Fig. 20-2c, p. 430
Insert “Temporal isolation
among cicadas”
temporal_isolation.swf
Prezygotic Barriers (2)
•
Behavioral isolation
•
•
distinctive courtship behaviors prevent mating
between species
Mechanical isolation
•
incompatible structural differences in
reproductive organs of similar species
Behavioral Isolation
Mechanical Isolation
Prezygotic Barriers (3)
•
Gametic isolation
•
gametes from different species are
incompatible because of molecular and
chemical differences
Postzygotic Barriers (1)
•
Hybrid inviability
•
•
interspecific embryos die during development
Hybrid sterility
•
prevents interspecific hybrids that survive to
adulthood from reproducing successfully
Hybrid Sterility
Postzygotic Barriers (2)
•
Hybrid breakdown
•
prevents offspring of hybrids that survive to
adulthood and successfully reproduce from
reproducing beyond one or a few generations
KEY CONCEPTS
•
The evolution of different species begins
with reproductive isolation, in which two
populations are no longer able to
interbreed successfully
Insert “Reproductive
isolating mechanisms”
isolating_mechanisms_m.swf
Explore reproductive isolation by
clicking on the figures in
ThomsonNOW
Learning Objective 3
•
What is allopatric speciation?
•
Give an example
Allopatric Speciation (1)
•
Evolution of a new species
•
•
from ancestral population
Population becomes geographically
isolated from rest of species
•
subsequently diverges
Allopatric Speciation (2)
•
More likely to occur if original isolated
population is small
•
•
makes genetic drift more significant
Examples:
•
•
•
Death Valley pupfishes
Kaibab squirrels
Porto Santo rabbits
Allopatric Speciation
KEY CONCEPTS
•
In allopatric speciation, populations
diverge into different species due to
geographic isolation, or physical
separation
Insert “Allopatric speciation
on an archipelago”
archipelago.swf
Explore allopatric speciation by
clicking on the figures in
ThomsonNOW.
Learning Objective 4
•
What is sympatric speciation?
•
Give plant and animal examples
Sympatric Speciation
•
Does not require geographic isolation
•
More common in plants than animals
Sympatric Speciation in Plants
•
Usually results from allopolyploidy
•
•
polyploid individual (>2 sets of chromosomes)
is hybrid derived from two species
Examples:
•
•
kew primroses
hemp nettles
Allopolyploidy
in Plants
Species A
2n=6
Species B
2n=4
P generation
n=2
n=3
Gametes
Hybrid AB
F1 generation
Fig. 20-9a, p. 435
No doubling of
chromosome number
Doubling of
chromosome number
2 n = 10
Chromosomes either
cannot pair or go
through erratic meiosis
Pairing now
possible
during meiosis
n=5
No gametes or sterile
gametes — no sexual
reproduction possible
Viable gametes — sexual
reproduction possible (selffertilization)
Fig. 20-9b, p. 435
Species A
2n=6
Species B
2n=4
P generation
n=2
n=3
Gametes
Hybrid AB
F1 generation
No doubling of
chromosome number
Doubling of chromosome
number
2 n = 10
Chromosomes either
Pairing now
cannot pair or go through
possible
erratic meiosis
n=5
during
meiosis
No gametes or sterile
gametes — no sexual
reproduction possible
Viable gametes — sexual
reproduction possible (selffertilization)
Stepped Art
Fig. 20-9b, p. 435
Sympatric Speciation
Sympatric Speciation in Animals
•
Fruit maggot flies
Sympatric Speciation in Animals
•
Cichlids
Fig. 20-12a, p. 437
Fig. 20-12b, p. 437
Fig. 20-12c, p. 437
KEY CONCEPTS
•
In sympatric speciation, populations
become reproductively isolated from one
another despite living in the same
geographic area
Insert “Sympatric
speciation in wheat”
wheat_speciation.swf
Explore sympatric speciation by
clicking on the figure in
ThomsonNOW.
Learning Objective 5
•
Debate the pace of evolution by
representing the views of either
punctuated equilibrium or gradualism
Evolution
•
Punctuated equilibrium model
•
•
•
evolution proceeds in spurts
short periods of active speciation
interspersed with long periods of stasis
Gradualism model
•
populations slowly diverge from one another
by accumulation of adaptive characteristics
Punctuated Equilibrium
and Gradualism
Stasis
Slow, gradual
changes
Extinction of
original species
Stasis
Stasis
Time
Time
Divergence
is sudden,
with rapid
changes
Stasis (little
change)
Structural changes
Divergence is
gradual
Structural changes
Fig. 20-13, p. 438
KEY CONCEPTS
•
Speciation may require millions of years
but sometimes occurs much more quickly
Learning Objective 6
•
What is macroevolution?
Macroevolution
•
Large-scale phenotypic changes in
populations
•
•
in taxonomic groups species level and higher
new species, genera, families, orders,
classes, phyla, kingdoms, or domains
KEY CONCEPTS
•
The evolution of species and higher taxa is
known as macroevolution
Learning Objective 7
•
Discuss novel features of macroevolution,
including preadaptations, allometric
growth, and paedomorphosis
Macroevolution
•
Includes evolutionary novelties
•
•
due to changes during development
Slight changes in regulatory genes
•
cause major structural changes in organism
Preadaptations
•
Structures originally fulfilled one role
•
•
changed and adapted for different role
Example: feathers
Allometric Growth
•
Varied rates of growth for different parts of
body
•
•
causes overall changes in shape of organism
Examples:
•
•
ocean sunfish
male fiddler crab
Allometric Growth
•
Ocean sunfish
Tail
approx. 1 mm
Newly hatched
ocean sunfish
Adult
ocean sunfish
Fig. 20-14a, p. 440
Fig. 20-14b, p. 440
Fig. 20-14b, p. 440
Paedomorphosis
•
Juvenile characteristics retained in adult
•
•
due to changes in timing of development
Example: adult axolotl salamanders
•
with external gills and tail fins
Paedomorphosis
•
Salamander
Learning Objective 8
•
What is the macroevolutionary significance
of adaptive radiation and extinction?
Adaptive Radiation (1)
•
Diversification of ancestral species into
many new species
•
Adaptive zones
•
new ecological opportunities not exploited by
ancestral organism
Adaptive Radiation (2)
•
When many adaptive zones are empty
•
•
colonizing species diversify and exploit them
Example: Hawaiian honeycreepers and
silverswords
•
after ancestors colonized Hawaiian Islands
Adaptive Radiation
•
Hawaiian honeycreepers
Rips away bark to
find insects
Maui parrot bill
Kauai
Sips flower nectar
‘I‘iwi
Oahu
Forages among
leaves and branches
Maui creeper
Maui
Chisels holes in
bark to get insects
Akiapolaau
Extinct Sipped
flower nectar
Black mamo
Extinct
Habits unknown
Ula-ai-hawane
Hawaii
Picks food from
cracks in the bark
Akialoa
Sips flower nectar
Apapane
Feeds on snails and
Sips flower nectar
invertebrates
Poo-uli
Crested honeycreeper
Fig. 20-16, p. 441
Adaptive Radiation
•
Hawaiian silverswords
Extinction (1)
•
Death of a species
•
When species become extinct
•
•
adaptive zones they occupied become vacant
allows other species to evolve and fill zones
Extinction (2)
•
Background extinction
•
•
continuous, low-level extinction of species
Mass extinction
•
•
extinction of numerous species, higher
taxonomic groups
in both terrestrial and marine environments
Mass
Extinction
Common
ancestor of
birds and
saurischians
Archosaur
common
ancestor
Fig. 20-18a, p. 443
Birds
Saurischians
(dinosaurs,
extinct)
Ornithischians
(dinosaurs,
extinct)
Pterosaurs
(flying reptiles,
extinct)
Crocodilians
(alligators,
crocodiles)
Fig. 20-18b, p. 443
Paleozoic
Permian
Triassic
Mesozoic
Jurassic
Theropods
(carnivorous
saurischians)
Archosaurs
Cenozoic
Cretaceous
Tertiary / Quaternary
Birds
Sauropods
(herbivorous
saurischians)
Common
ancestor
Stegosaurs
and other
ornithischians
Crocodilians
Pterosaurs
Crocodiles
Fig. 20-18b, p. 443