4. “That mystery of mysteries…”
Darwin never actually tackled
how new species arose…
5. “That mystery of mysteries…”
Darwin never actually tackled
how new species arose…
Both in space and time,
we seem to be brought
somewhat near to that great fact
—that mystery of mysteries—
the first appearance of
new beings on this Earth.
7. So…what is a species?
§ Biological species concept
8. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
9. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
u reproductively compatible
10. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
u reproductively compatible
Eastern Meadowlark Western Meadowlark
11. So…what is a species?
§ Biological species concept
u population whose members can
interbreed & produce viable, fertile
offspring
u reproductively compatible
Distinct species:
songs & behaviors are different
enough to prevent interbreeding
Eastern Meadowlark Western Meadowlark
13. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
14. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
15. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
16. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
17. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
18. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
19. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
20. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
21. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
§ geographic separation
22. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
§ geographic separation
u sympatric
23. How and why do new species originate?
§ Speciation: formation of a new species by the
splitting of an existing species
§ Species are created by a series of
evolutionary processes
u populations become isolated due to various
isolating mechanisms
§ geographically isolated
§ reproductively isolated, etc.
u isolated populations
evolve independently
§ Isolation
u allopatric
§ geographic separation
u sympatric
§ still live in same area
35. Ammospermophilus spp
Geographic isolation
§ Species occur in different areas
u physical barrier
u allopatric speciation
§ “other country”
Harris’s antelope
squirrel inhabits
the canyon’s
south rim (L). Just
a few miles away
on the north rim
(R) lives the
closely related
white-tailed
antelope squirrel
36.
37. • Within each population there are
breeding subunits called demes
38. • Within each population there are
breeding subunits called demes
• Individuals within a deme tend to
breed with each other more
often than with members of
other demes.
39. • Within each population there are
breeding subunits called demes
• Individuals within a deme tend to
breed with each other more
often than with members of
other demes.
• They remain part of the same gene pool, but
…gene flow between separate demes slows, and…
… may even stop.
40. • Within each population there are
breeding subunits called demes
• Individuals within a deme tend to
breed with each other more
often than with members of
other demes.
• They remain part of the same gene pool, but
…gene flow between separate demes slows, and…
… may even stop.
• Each deme may evolve along separate lines, so…
…when reunited they may no longer be able to
interbreed
41. Speciation may occur where different parts of a
population of a species become isolated from
one another.
42. Speciation may occur where different parts of a
population of a species become isolated from
one another.
Example: a species of butterfly is widely distributed
across an area of grassland.
43. Speciation may occur where different parts of a
population of a species become isolated from
one another.
Example: a species of butterfly is widely distributed
across an area of grassland.
47. Climate changes
cause the area to
become wetter… …and a river forms
Because the
butterflies are not
strong fliers…
48. Climate changes
cause the area to
become wetter… …and a river forms
Because the
butterflies are not
strong fliers… …they cannot cross the
river
49. Climate changes
cause the area to
become wetter… …and a river forms
Because the
butterflies are not
strong fliers… …they cannot cross the
river
The two groups of butterflies are now isolated from
each other
53. The selective
pressures are different
on either side of the
river, so…
…the two populations
evolve different wing
patterns
54. NOTE: At this stage
the two populations
may not be different
enough to be
considered as two
separate species…
55. NOTE: At this stage
the two populations
may not be different
enough to be
considered as two
separate species…
…they may be considered
as subspecies or varieties.
60. The two populations of
butterfly can now mix
together, but…
…successful mating requires that they
recognise each other by wing pattern, so…
61. The two populations of
butterfly can now mix
together, but…
…successful mating requires that they
recognise each other by wing pattern, so…
…they do not interbreed.
62. The two populations of
butterfly can now mix
together, but…
…successful mating requires that they
recognise each other by wing pattern, so…
…they do not interbreed.
The two populations are now definitely different species.
67. Sympatric Speciation
•Speciation which occurs when some factor (other
than geographic barriers) prevents two populations
living in the same area from interbreeding
68. Sympatric Speciation
•Speciation which occurs when some factor (other
than geographic barriers) prevents two populations
living in the same area from interbreeding
•‘Sympatric’ means ‘same fatherland’
69. Ecological isolation
§ Species occur in same area, but occupy
different habitats so rarely encounter
each other
70. Ecological isolation
§ Species occur in same area, but occupy
different habitats so rarely encounter
each other
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial
71. Ecological isolation
§ Species occur in same area, but occupy
different habitats so rarely encounter
each other
2 species of garter snake, Thamnophis,
occur in same area, but one lives in water &
other is terrestrial
lions & tigers could
hybridize, but they
live in different
habitats:
§ lions in grasslands
§ tigers in rainforest
72. Temporal isolation
§ Species that breed during different
times of day, different seasons, or
different years cannot mix gametes
u sympatric speciation
§ “same country”
73. Temporal isolation
§ Species that breed during different
times of day, different seasons, or
different years cannot mix gametes
u sympatric speciation
§ “same country”
Eastern spotted skunk
(L) & western spotted
skunk (R) overlap in
range but eastern mates
in late winter & western
mates in late summer
75. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
Blue footed boobies mate
only after a courtship display
unique to their species
76. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
u identifies members of species
Blue footed boobies mate
only after a courtship display
unique to their species
77. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
u identifies members of species
u attract mates of same species
Blue footed boobies mate
only after a courtship display
unique to their species
78. sympatric speciation?
Behavioral isolation
§ Unique behavioral patterns & rituals isolate species
u identifies members of species
u attract mates of same species
§ courtship rituals, mating calls
Blue footed boobies mate
only after a courtship display
unique to their species
80. Recognizing your
own species
courtship display of
Gray-Crowned Cranes, Kenya
81. Recognizing your
own species
courtship display of
Gray-Crowned Cranes, Kenya
What can you say?
82. Recognizing your
own species
courtship songs of sympatric
species of lacewings
courtship display of
Gray-Crowned Cranes, Kenya
firefly courtship displays
85. Sympatric speciation: Example 1
Chiffchaff Willow warbler
(Phylloscopus (Phylloscopus trochilus)
collybita)
Two small insect-eating birds
which spend summer in Britain
86. Sympatric speciation: Example 1
Chiffchaff Willow warbler
(Phylloscopus (Phylloscopus trochilus)
collybita)
Two small insect-eating birds
which spend summer in Britain
They are difficult to tell apart by their appearance.
87. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
88. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
Their songs are
very different
89. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
Their songs are
very different
Successful mating will only result from the correct
behaviour pattern, so…
90. For both species,
their songs are an important part of courtship
Willow warbler Chiffchaff
Their songs are
very different
Successful mating will only result from the correct
behaviour pattern, so…
… willow warblers and chiffchaffs do not interbreed
95. Example 3: Production of Infertile Hybrids
Carrion crow Hooded crow
(Corvus corone) (Corvus cornix)
96. Example 3: Production of Infertile Hybrids
Carrion crow Hooded crow
(Corvus corone) (Corvus cornix)
Found in England, Found in Northern
Wales and Scotland and
Southern Scotland Ireland
98. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
99. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
… carrion crows and hooded crows do interbreed to
produce hybrids, but…
100. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
… carrion crows and hooded crows do interbreed to
produce hybrids, but…
… hybrids are not as fertile as the parents, so…
101. Carrion crow Hooded crow
Territories of the
two species do
overlap slightly,
so…
… carrion crows and hooded crows do interbreed to
produce hybrids, but…
… hybrids are not as fertile as the parents, so…
… selection favours the parents.
103. sympatric speciation?
Mechanical isolation
§ Morphological differences can prevent
successful mating
Plants
Even in closely related
species of plants, the
flowers often have distinct
appearances that attract
different pollinators.
These 2 species of monkey
flower differ greatly in
shape & color, therefore
cross-pollination does not
happen.
109. Bees can distinguish between corn poppies and other
species of poppy.
Papaver alpinum Papaver orientale Papaver somniferum
Bees visiting one species will not visit another
species, so…
110. Bees can distinguish between corn poppies and other
species of poppy.
Papaver alpinum Papaver orientale Papaver somniferum
Bees visiting one species will not visit another
species, so…
…pollen is not transferred between species and
interbreeding does not occur.
112. Mechanical isolation Animals
§ For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
Damsel fly penises
113. Mechanical isolation Animals
§ For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
u lack of “fit” between sexual organs:
hard to imagine for us… but a big issue for insects with
different shaped genitals!
Damsel fly penises
114. Mechanical isolation Animals
§ For many insects, male &
female sex organs of
closely related species do
not fit together, preventing
sperm transfer
u lack of “fit” between sexual organs:
hard to imagine for us… but a big issue for insects with
different shaped genitals!
I can’t even imagine!
Damsel fly penises
116. sympatric speciation?
Gametic isolation
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
117. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
118. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
119. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
120. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
w receptor recognition: lock & key between egg & sperm
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
121. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
w receptor recognition: lock & key between egg & sperm
§ chemical incompatibility
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
122. sympatric speciation?
Gametic isolation
§ Sperm of one species may not be able to fertilize
eggs of another species
u mechanisms
§ biochemical barrier so sperm cannot penetrate egg
w receptor recognition: lock & key between egg & sperm
§ chemical incompatibility
w sperm cannot survive in female reproductive tract
Sea urchins release sperm
& eggs into surrounding
waters where they fuse &
form zygotes. Gametes of
different species— red &
purple —are unable to fuse.
125. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
u reduced hybrid viability
zebroid
126. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
u reduced hybrid viability
u reduced hybrid fertility
zebroid
127. Post-reproduction barriers
§ Prevent hybrid offspring from
developing into a viable, fertile adult
u reduced hybrid viability
u reduced hybrid fertility
u hybrid breakdown
zebroid
129. sympatric speciation?
Reduced hybrid viability
§ Genes of different parent species may
interact & impair the hybrid’s development
Species of salamander
genus, Ensatina, may
interbreed, but most
hybrids do not complete
development & those
that do are frail.
132. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
133. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
134. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
135. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
136. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64
chromosomes
(32 pairs)
137. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) (31 pairs)
138. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)
139. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)
140. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)
141. Reduced hybrid fertility
§ Even if hybrids are vigorous
they may be sterile
u chromosomes of parents may differ in number
or structure & meiosis in hybrids may fail to
produce normal gametes
Mules are vigorous,
but sterile
Horses have 64 Donkeys have 62
chromosomes chromosomes
(32 pairs) Mules have 63 chromosomes! (31 pairs)
143. sympatric speciation?
Hybrid breakdown
§ Hybrids may be fertile & viable in first
generation, but when they mate offspring
are feeble or sterile
In strains of cultivated rice,
hybrids are vigorous but
plants in next generation are
small & sterile.
On path to separate species.
144. Speciation through Polyploidy
§ Polyploidy results from failed meiosis
which leads to an organism that has
two sets of chromosomes.
§ Polyploid types are labelled according
to the number of chromosome sets in
the nucleus
ex. Tetraploid, hexaploid, etc.
145. Polyploidy
§ Most common in plants because they are able
to self-fertilize
§ 2n + 2n = 4n
§ Most polyploids display heterosis relative to
their parental species, and may display
variation or morphologies that may contribute
to the process of speciation
§ Polyploid plants, even though they are sterile
can reproduce vegetatively. Through chance,
the chromosome number may double again,
making it fertile again…and therefore a new
species!
146. Rate of Speciation
Niles Eldredge
Curator
American Museum of Natural History
147. Rate of Speciation
§ Current debate:
Niles Eldredge
Curator
American Museum of Natural History
148. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
Niles Eldredge
Curator
American Museum of Natural History
149. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
Niles Eldredge
Curator
American Museum of Natural History
150. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
Niles Eldredge
Curator
American Museum of Natural History
151. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
Niles Eldredge
Curator
American Museum of Natural History
152. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
u Punctuated equilibrium
Niles Eldredge
Curator
American Museum of Natural History
153. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
u Punctuated equilibrium
§ Stephen Jay Gould
Niles Eldredge
Curator
American Museum of Natural History
154. Rate of Speciation
§ Current debate:
Does speciation happen gradually or
rapidly
u Gradualism
§ Charles Darwin
§ Charles Lyell
u Punctuated equilibrium
§ Stephen Jay Gould
§ Niles Eldredge
Niles Eldredge
Curator
American Museum of Natural History
157. Gradualism
§ Slow change from
one form to another
§ Gradual divergence
over long spans of
time
158. Gradualism
§ Slow change from
one form to another
§ Gradual divergence
over long spans of
time
u assume that big
changes occur as
the accumulation
of many small ones
162. Punctuated Equilibrium
§ Rate of speciation is
not constant
u rapid bursts of
change
u long periods of little
or no change
Time
163. Punctuated Equilibrium
§ Rate of speciation is
not constant
u rapid bursts of
change
u long periods of little
or no change
u species undergo
rapid change when
they 1st bud from
parent population
Time
164. Stephen Jay Gould (1941-2002)
§ Harvard paleontologist &
evolutionary biologist
u punctuated equilibrium
u prolific author
§ popularized evolutionary thought
166. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
167. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
168. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well
169. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well
170. Evolution is not goal-oriented
An evolutionary trend does not mean that
evolution is goal-oriented.
Surviving species
do not represent
the peak of
perfection. There
is compromise &
random chance
involved as well
Remember that for
humans as well!
