Download document

Chapter 14
The Origin of Species
RAPID EVOLUTION
• One example of rapid evolution occurred among
mosquitoes who migrated into the London
underground
• In less than 150
years, Culex pipiens
evolved into a new
mosquito species,
Culex molestus
• The origin of new
species is called
speciation
• The isolated mosquitoes adapted to their new
underground environment
– They altered their prey, mating habits, and breeding
patterns
• Environmental barriers that isolate populations
are just one of many mechanisms in the
evolution of species
CONCEPTS OF SPECIES
What is a species?
• Linnaeus used physical appearance to identify
species when he developed the binomial system
of naming organisms
– This system established the basis for taxonomy
• But appearance alone does not always define a
species
– Example: eastern and western meadowlarks
Figure 14.1A
• Similarities between some species and variation
within a species can make defining species
difficult
– Humans exhibit extreme physical diversity
Figure 14.1B
• A ring species may illustrate the process of
speciation
1
OREGON
POPULATION
Sierra
Nevada
COASTAL
POPULATIONS
Yelloweyed
Yellowblotched
2
Gap in
ring
Monterey
INLAND
POPULATIONS
Largeblotched
3
Figure 14.1C
• The biological species concept is not applicable
to fossils or asexual organisms
• Most organisms are classified based on observable
phenotypes
– The morphological species concept
• The genealogical species concept defines a species
as a cluster of organisms representing a specific
evolutionary lineage
• The ecological species concept defines a species
by its ecological role
•
Reproductive barriers keep species
separate
Prezygotic and
postzygotic
reproductive
barriers prevent
individuals of
different species
from interbreeding
Table 14.2
• Courtship ritual in blue-footed boobies is an
example of one kind of prezygotic barrier,
behavioral isolation
• Many plant species have
flower structures that are
adapted to specific
pollinators
– This is an example of
mechanical isolation,
another prezygotic barrier
Figure 14.2A, B
• Hybrid sterility is one type of postzygotic barrier
– A horse and a
donkey may produce
a hybrid offspring, a
mule
– Mules are sterile
Figure 14.2C
MECHANISMS OF SPECIATION
Geographic isolation can lead to
speciation
• When a population is cut off from its parent
stock, species evolution may occur
– An isolated population may become genetically
unique as its gene pool is changed by natural
selection, genetic drift, or mutation
– This is called allopatric speciation
Figure 14.3
Islands are living laboratories of
speciation
• On the
Galápagos
Islands,
repeated
isolation and
adaptation
have resulted
in adaptive
radiation of
14 species of
Darwin’s
finches
Figure 14.4A
• Adaptive radiation on an island chain
1
A
Species A
from mainland
2
B
B
3
B
C
B
4
C
C D
C
C
D
5
Figure 14.4B
New species can also arise within
the same geographic area as the
parent species
• In sympatric speciation, a new species may arise
without geographic isolation
– A failure in meiosis can produce diploid gametes
– Self-fertilization can then produce a tetraploid zygote
Parent species
Zygote
Meiotic
error
Selffertilization
2n = 6
Diploid
Offspring may
be viable and
self-fertile
4n = 12
Tetraploid
Unreduced diploid gametes
Figure 14.5A
• Sympatric speciation by polyploidy was first
discovered by Dutch botanist Hugo de Vries in
the early 1900s
Figure 14.5B
Connection: Polyploid plants clothe
and feed us
• Many plants are polyploid
– They are the products of
hybridization
– The modern bread wheat is
an example
Figure 14.6A
• The evolution
of wheat
AA
BB
Wild
Triticum
(14 chromosomes)
Triticum
monococcum
(14 chromosomes)
AB
Sterile hybrid
(14 chromosomes)
Meiotic error and
self-fertilization
AABB
DD
T. turgidum
EMMER WHEAT
(28 chromosomes)
T. tauschii
(wild)
(14 chromosomes)
ABD
Sterile hybrid
Meiotic error and
self-fertilization
AA BB DD
T. aestivum
BREAD WHEAT
(42 chromosomes)
Figure 14.6B
Reproductive barriers may evolve as
populations diverge
• This has been
documented
by
Initial sample
of fruit flies
Starch medium
Maltose medium
Results of
mating experiments
Female
populations
Same
Different
8
20
Mating frequencies
in experimental group
Same
9
Different
22
Male
populations
Female
Starch
Maltose
Male
Maltose Starch
– laboratory
studies
(fruit flies)
18
15
12
15
Mating frequencies
in control group
Figure 14.7A
– examples in natural populations
(pupfish in Death Valley)
Figure 14.7B
The tempo of speciation can appear
steady
or
jumpy
• According to the
gradualist model of the
origin of species
– new species evolve by
the gradual accumulation
of changes brought about
by natural selection
• However, few gradual
transitions are found in
the fossil record
Figure 14.8A
• The punctuated
equilibrium model
suggests that speciation
occurs in spurts
– Rapid change occurs
when an isolated
population diverges from
the ancestral stock
– Virtually no change
occurs for the rest of the
species’ existence
Figure 14.8B