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Chapter 24
The Origin of
Species
Species
Hummingbirds of Costa Rica
Species
Biological Species Concept
A population whose members can
potentially interbreed in nature
to produce viable, fertile offspring
In practice, we recognize two populations as
separate species if each has distinguishing
characteristics relative to the other, and
members of each population lack the
potential to interbreed in nature with
members of the other population
Reproductive Barriers
Isolate populations from one another
A complete barrier
would result in no
gene flow
An incomplete
barrier could still
reduce gene flow
Reproductive Barriers
Pre-zygotic vs. post-zygotic
A complete barrier
would result in no
gene flow
An incomplete
barrier could still
reduce gene flow
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Eurasian spoonbill
Roseate spoonbill
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
North America
Madagascar
Central America
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Rhagoletis pomonella
Hawthorns or apples
for oviposition
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Galapagos
Islands
Red-footed booby
Blue-footed boobies
Satin Bowerbirds & their
bowers
Australia
Tooth-billed Catbird’s
leaf display
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Temporal isolation
Dog-day
(17 year)
Periodical
(12 year)
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Temporal isolation
Mechanical isolation
C. wapleri
Thompson Creek, W. Feliciana Parish
Reproductive Barriers
Pre-zygotic
Habitat isolation
Geographic isolation
Ecological isolation
Behavioral (mate choice) isolation
Temporal isolation
Mechanical isolation
Gametic isolation
head
acrosome
tail
midpiece
ovum
Buffon (1811)
Reproductive Barriers
Post-zygotic
Reduced hybrid viability
Reduced hybrid fertility
Hybrid sterility (in the extreme)
♀
x
=
♂
sterile
Reproductive Barriers
Post-zygotic
Reduced hybrid viability
Reduced hybrid fertility
Hybrid sterility (in the extreme)
Hybrid breakdown
(reduced viability or fertility
occurs in the offspring of
hybrids)
Reproductive Barriers
Habitat
isolation
Temporal
isolation
Individuals
of different
species
HABITAT ISOLATION
Behavioral
isolation
Mechanical
isolation
Mating
attempt
TEMPORAL ISOLATION
Figure 24.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
BEHAVIORAL ISOLATION
MECHANICAL ISOLATION
Reproductive Barriers
Gametic
isolation
Reduce
hybrid
viability
Fertilization
GAMETIC ISOLATION
REDUCED HYBRID
VIABILITY
Figure 24.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Reduce
hybrid
fertility
Hybrid
breakdown
Viable
fertile
offspring
REDUCED HYBRID FERTILITY HYBRID BREAKDOWN
Speciation
The process by which new species form
Two requirements:
Reproductive isolation of
populations (gene flow
sufficiently reduced)
Genetic divergence (divergent
evolution)
Two main modes:
Allopatric vs. sympatric
Allopatric speciation
Divergence occurs in geographic isolation
Sympatric speciation
Divergence occurs despite lack of geographic isolation
Allopatric vs. sympatric speciation
Figure
24.5
Sympatric speciation
Rhagoletis pomonella
Hawthorns or apples
for oviposition
Sympatric speciation
Divergence occurs despite lack of geographic isolation
Polyploids
Organisms with extra sets of
chromosomes; can result in sympatric
speciation in one generation
The origin of a polyploid individual is
usually a mistake in meiosis or mitosis
Autopolyploidy vs. allopolyploidy
Sympatric speciation
An autopolyploid
Is an individual that has > two chromosome
sets, all from a single species
Failure of cell division
in a cell of a growing
diploid plant produces a
tetraploid branch.
Gametes produced
by flowers on this
branch will be diploid.
If offspring are viable
and fertile, it is a new
biological species.
2n
2n = 6
4n = 12
Figure 24.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4n
Sympatric speciation
An allopolyploid
Is an individual with > two chromosome sets,
derived from different species
Unreduced gamete
with 4 chromosomes
Hybrid with
7 chromosomes
Species A
2n = 4
Unreduced gamete
with 7 chromosomes
Viable fertile
hybrid
Meiotic error;
chromosome
number not
reduced from
2n to n
2n = 10
Normal gamete
n=3
Species B
2n = 6
Figure 24.9
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Normal gamete
n=3
Polyploidy is
especially common
in plants
From Micro- to MacroEvolution
Microevolution –
Population and
species-level
evolution,
including
speciation
Macroevolution –
Speciation and
all broader-scale
evolutionary
patterns and
processes
Anagenesis
Sufficient microevolutionary
changes may
occur that
the earlier
population is
considered a
separate species
from the later
population
Figure
24.2
time
Cladogenesis
Branching
evolution
occurs as
speciation
events
accumulate.
The formation
of each new
branch is a
macroevolutionary
event.
Anagenesis
Sufficient microevolutionary
changes may
occur that
the earlier
population is
considered a
separate species
from the later
population
Figure
24.2
time
Cladogenesis
Branching
evolution
occurs as
speciation
events
accumulate
The formation
of each new
branch is a
macroevolutionary
event
Broad patterns across
the resulting tree are
also within the scope
of macroevolution
Adaptive Radiation
One species gives rise to many others in a
geologically short period of time
E.g., Darwin’s
finches
Islands are
good places to
find adaptive
radiations
Adaptive Radiation
E.g., Hawaiian silverswords
Figure 24.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Tempo of Evolution
time
Gradualism
Figure 24.13
Punctuated
Equilibrium
Tempo of Evolution
time
Gradualism
Figure 24.13
Punctuated
Equilibrium
Evolutionary Novelties
Evolutionary
novelties usually
arise as
modifications of
existing traits
Figure 24.14
Evolutionary Development (Evo-Devo)
Slight alterations in development can have
profound effects on adults
Heterochrony =
change in the
rate or timing of
development,
relative to an
ancestor
E.g., paedomorphosis = heterochronic
retention of juvenile structures in
adulthood
Evolutionary Development (Evo-Devo)
Slight alterations in development can have
profound effects on adults
Heterotopy = change
in the physical
position of a trait
during development,
relative to an
ancestor
E.g., feathers from one
part of a bird’s body
may become expressed
on another part
Evolutionary Development (Evo-Devo)
Allometric growth =
relative growth rates
of different body
parts within a
species during
development
Evolutionary Development (Evo-Devo)
Allometric growth =
relative growth rates
of different body
parts within a
species during
development
E.g., allometric
growth in horned
scarab beetles;
certain clusters of
cells grow faster than others
Evolutionary Development (Evo-Devo)
Evolutionary Development (Evo-Devo)
Phanaeus imperator
Evolution is not “goal oriented”
Evolution is a genetic response to the interaction
between the individuals of a population and their
current environment (which includes other
individuals)
Natural selection can only act on the phenotypic
variation present, and selection can only cause
evolutionary change if phenotypic variation
results (at least in part) from genetic variation
Evolution is not “goal oriented”
Therefore, even if female tigers in a population
would prefer blue males, blue tigers will never
evolve if the population lacks variation that
includes blue fur
YES! But he
exists only
in my dreams.
He’s not blue,
but he’s better
than nothing!