Download The Origin of Species

The Origin of Species
AP Chapter 24
Microevolution vs macroevolution
• Microevolution – changes in gene
frequencies within population
• Macroevolution – origin of new
taxonomic groups, ie – species level
and above
Speciation is at the boundary
between microevolution and
macroevolution.
What is a species?
•Species is a Latin word meaning “kind”
or “appearance.”
•Traditionally, morphological differences
have been used to distinguish species.
•Today, differences in body function,
biochemistry, behavior, and genetic
makeup are also used to differentiate
species.
4 approaches to species concept
1. Biological – reproductive isolation
2. Morphological – anatomical
differences
3. Ecological – unique roles in
environment
4. Phylogenetic – based on evolutionary
lineage with distinct morphology and
molecular sequences
Mayr’s concept of species
• 1942
• Potential to interbreed and
produce fertile offspring
The biological species concept is based on
interfertility rather than physical similarity
Figure 24.2a
Figure 24.2b The biological species concept is based on interfertility
rather than physical similarity
Interfertility concept does
not apply to
• Asexually reproducing organisms
• Extinct species
Barriers to speciation
• Prezygotic – prevent mating or
successful fertilization
• Postzygotic - prevent the
hybrid zygote from developing
into a viable, fertile adult.
Prezygotic barriers
• Habitat isolation
• Temporal isolation – different breeding
times
• Behavioral isolation
• Mechanical isolation
• Gametic isolation
Fig. 24-4h
(f)
Mechanical Isolation
Bradybaena with shells
spiraling in opposite
directions
Fig. 24-4e
(c)
Temporal Isolation
Eastern spotted skunk
(Spilogale putorius)
Western spotted skunk
(Spilogale gracilis)
These skunks have different breeding times.
Fig. 24-4g
(e)
Behavioral Isolation
Courtship ritual of bluefooted boobies
Fig. 24-4k
(g)
Gametic
isolation in sea urchins
Sea urchins – Their gametes will not fuse with
other gametes of other species.
Postzygotic Barriers
•Reduced hybrid viability - Genetic incompatibility
between the two species may abort the development of
the hybrid at some embryonic stage or produce frail
offspring.
•Reduced hybrid fertility - Even if the hybrid offspring
are vigorous, the hybrids may be infertile and the
hybrid cannot backbreed with either parental species.
Reduced hybrid breakdown – In some cases, first
generation hybrids are viable and fertile.However,
when they mate with either parent species or with each
other, the next generation is feeble or sterile.
Fig. 24-4m
Reduced Hybrid Fertility
(i)
Mules are infertile.
Modes of speciation
1) Allopatric – geographical separation
Figure 24.7 Allopatric speciation of squirrels in the Grand Canyon
Modes of speciation
2. Sympatric – biological barriers prevent
gene flow in overlapping populations
as in autopolyploidy, allopolyploidy,
mate preference, etc.
Figure 24.8 Has speciation occurred during geographic isolation?
Examples of Sympatric Speciation involving
polyploidy (extra sets of chromosomes) which
can lead to new species.
• Autopolyploidy – more than two sets of
chromosomes; meiotic failure of
chromosomes to separate, common in selfpollination in plants
• Allopolyploidy * – interspecific hybrid; may
become fertile due to nondisjunction in
formation of gametes
• * more common
Sympatric speciation by autopolyploidy in plants
Notice that the chrom
do not separate!
Figure 24.15
One mechanism for allopolyploid speciation in
plants
“allo” means coming from another place,
in this case another species.
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)
• Around 1870, a new species of grass turned up at the salt
marches near the coast of the English Channel: Spartina
townsendii . It was taller than the indigenous Spartina
alternifolia.
• Another relative, Spartina stricta, inhabits the NorthAmerican east coast. It was brought in to Europe and
began to occupy the sites of Spartina alternifolia.
• It was now suspected that Spartina townsendii was a
hybrid of the two original species. The fact that Spartina
townsendii has 2n = 126 chromosomes, Spartina
alternifolia has 2n = 70 and Spartina stricta has 2n = 56
chromosomes makes this suggestion seem likely.
Modes of Speciation
3. Parapatric Speciation
• Involves both time and space
• Is speciation at the perimeter of the ancestral
species range where the environment
changes in a qualitative way
• Local environment or resources available at
the margin of the species range are
sufficiently different that natural selection
selects for different adaptations
• Natural selection would be against the
hybrids
Hybrid zones
• Where divergent allopatric and
parapatric populations come back and
interbreed
Three outcomes…
With renewed or continued contact between two
populations, there are three possible outcomes:
1. Individuals can hybridize readily.
No speciation
2. Individuals do not hybridize at all (reinforcement)
Full speciation
3. Individuals hybridize but offspring
have reduced fitness.
Speciation in progress. Selection for evolution of strong
reproductive barriers.
32
Fig. 24-14-4
Strengthening of
reproductive
barriers
Isolated population
diverges
Possible
outcomes:
Hybrid
zone
Reinforcement
OR
Fusion
Gene flow
Hybrid
OR
Barrier
to is great
If gene
flow
gene flow
Population
enough,
the parent species
Stability
(five individuals
can
fuse
into
a
single
are shown)
species
Hybrids continue to be produced between
the two species in the area of their
overlap, but the gene pools of both parent
species remain distinct.
Fig. 24-15
Sympatric male
pied flycatcher
28
Allopatric male
pied flycatcher
Pied flycatchers
24
Collared flycatchers
Number of females
Reinforcement
of barriers to
reproduction,
has to be
strong in
sympatric
species
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. 24-16
Pundamilia nyererei
Pundamilia pundamilia
Gene pools
have fused.
Pundamilia “turbid water,”
hybrid offspring from a location
with turbid water
Timing of evolution?
• Gradual (Lyell, Darwin)
• Punctuated equilibrium (Gould) –
evolution occurs in spurts and
interspersed within long periods of
stasis
Species undergo
most morphological modifications
when they
first bud from their
parent
population.
After establishing
themselves
as separate
species, they
remain static for
the vast
majority of their
existence.
Anagenesis vs cladogenesis
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
Case Study
As the Worm Turns:
Are apple maggot
flies and hawthorn
maggot flies
different species?
5 primary forces affect genetic
composition of populations and cause
evolution
•
•
•
•
•
Natural selection
Mutation
Gene flow
Genetic drift
Mate choice
Species
• Species contain groups of
interbreeding populations connected
by gene flow.
• The species is a natural and
fundamental unit of evolution
• Each species is the product of a unique
and independent evolutionary pathway.
How to define species
• Biological concept – reproductively
isolation
• Phylogenetic concept – if a
phylogenetic tree, each species
uniquely occupies the tip of a tree
branch
• Morphological concept – consistent,
distinguishing physical differences
• Ecological concept
How species form:
Allopatric
Sympatric
Parapatric
Founder Effect
Three outcomes if hybridization
With renewed or continued contact between two
populations, there are three possible outcomes:
1. Individuals can hybridize readily.
No speciation
2. Individuals do not hybridize at all.
Full speciation
3. Individuals hybridize but offspring
have reduced fitness.
Speciation in progress. Selection for evolution of strong
reproductive barriers.
46
How hybrids determine species
• Are they reproductively isolated?
• Can they interbreed back with parent
groups?
• Are they a separate but “weak” group
that can interbreed?
1. Are they different species?
2. What species definition might apply here?
3. If they are (or are you thinking they might be),
how did the speciation occur? Develop this
idea.
4. Which evidences are the most important for
your choice? Star those on your sheet.
5. What else do you need to know to validate your
conclusion? Go online and research what you
can find out. Think of a specific question you
are trying to answer. (HW)
Test Review
• About Darwin
• Evolution as defined by Darwin and concept today
• Scientists/theories influenced development of the
theory
• Points of Darwin’s Theory
• Evidences (4) for evolution
• Homologous vs analogous structures
• Vestigial structures
• Microevolution vs macroevolution
• Origins of genetic variation
• Average heterozygosity
• Hardy-Weinberg – how to do problems, conditions that
maintain genetic equilibrium
• How gene frequencies can be altered
• Difference in types of genetic drift – bottleneck, founder
effect
• Relative fitness
• Types of natural selection
• Sexual selection – types
• How to preserve genetic variation
• 4 concepts of species
• Types of reproductive isolation (prezygotic and
postzygotic, types of each)
• 3 main types of speciation, how differ
• Autoploidy and allopolyploidy in sympatric speciation
• Role of hybrids in determining speciation
• Punctuated equilibrium vs gradual change in timing of
evolution