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Transcript
Today…
• Turn in your Hardy Weinberg labs &
practice problems
• Turn in PKU Case Study
• Test corrections due FRIDAY
• Today – Speciation & Cladograms! 
1
The Origin of Species
Mom, Dad…
There’s something
you need to know…
I’m a MAMMAL!
2010-2011
Speciation
• Changes in allele frequency are so
great that a new species is formed
• Can be slow and gradual or in
“bursts”
• Extinction rates can be rapid and
then adaptive radiation follows
when new habitats are available
Correlation of speciation to food sources
Seed
eaters
Flower
eaters
Insect
eaters
Rapid speciation:
new species filling niches,
because they inherited
successful adaptations.
Adaptive radiation
So…what is a species?
• Population whose members can
interbreed & produce viable, fertile
offspring
• Reproductively compatible
Distinct species:
songs & behaviors are different
enough to prevent interbreeding
Eastern Meadowlark Western Meadowlark
How do new species originate?
• When two populations become
reproductively isolated from each other.
• Speciation Modes:
– allopatric
• geographic separation
• “other country”
– sympatric
• still live in same area
• “same country”
Allopatric Speciation
 Physical/geographical
separation of two
populations
 Allele frequencies diverge
 After a length of time the two
population are so different
that they are considered
different species
 If the barrier is removed
interbreeding will still not
occur due to pre/post zygotic
isolation
Sympatric Speciation
Formation of a new species without geographic isolation.
Causes:
– Pre-zygotic barriers exist to mating
– Polyploidy (only organism with an even number of
chromosomes are fertile…speciation occurs quickly)
– Hybridization: two different forms of a species mate in
common ground (hybrid zone) and produce offspring
with greater genetic diversity than the
parents….eventually the hybrid diverges from both sets
of parents
Sympatric Speciation
Gene flow has been reduced between flies that feed on
different food varieties, even though they both live in the
same geographic area.
Pre-zygotic Isolation
Sperm never gets a chance to meet egg
•Geographic isolation: barriers prevent
mating
•Ecological isolation: different habitats in
same region
•Temporal isolation: different populations
are fertile at different times
•Behavior Isolation: they don’t recognize
each other or the mating rituals
•Mechanical isolation: morphological
differences
•Gamete Isolation: Sperm and egg do not
recognize each other
PRE-Zygotic barriers
• Obstacle to mating or to fertilization if
mating occurs
geographic isolation
behavioral isolation
ecological isolation
temporal isolation
mechanical isolation
gametic isolation
Post Zygotic Isolation
• Hybrid Inviability –
the embryo cannot
develop inside the
mothers womb
• Hybrid Sterility –
Adult individuals can
be produced BUT
they are not fertile
• Hybrid Breakdown –
each successive
generation has less
fertility than the
parental generation
Evolutionary Time Scale
• Microevolution – changing
of allele frequencies in a
population over time.
• Macroevolution – patterns
of change over geologic
time. Determines
phylogeny
– Gradualism – species
are always slowly
evolving
– Punctuated equilibrium –
periods of massive
evolution followed by
periods with little to no
evolution
Patterns of Evolution
• Divergent Evolution (adaptive radiation)
• Convergent Evolution
– Two or more species that share a common
environment but not a common ancestor
evolve to be similar
Is it a shark or a
dolphin??
Coevolution
• Two or more species
reciprocally
affect each other’s evolution
– predator-prey
• disease & host
– competitive species
– mutualism
• pollinators & flowers
Not Necessarily on Purpose:
Domestication and Speciation
in the Canidae Family
Did Dogs Co-evolve with
Humans?
16
Who is Who’s Best Friend?
The dog is said to be a man’s (human’s)
best friend, but it could also be said that
we are a dog’s best friend.
Objectives:
– How to interpret phylogenetic diagrams.
– Understand how natural selection can work
on a population to cause speciation.
– Distinguish between natural and artificial
selection.
17
Dog Breeds
The winner of Best of Show
at the 2009 Westminster
Dog Show was a Sussex
Spaniel.
“Stump” the spaniel competed against
170 other breeds of domestic dog (an
intraspecies competition).
Where do so many breeds come from?
How did the species we recognize as the
domestic dog arise?
18
The start of our story…
A young boy is sitting near the edge of a cave 20,000
years ago. He has just taken out the garbage from the
group’s previous day’s activities. The garbage consists
of mostly bones and scraps of food from a recent
successful hunt. As dusk approaches, the wolves start
to arrive. The boy is not frightened. He has seen the
wolves many times before. In fact, their arrival is almost
ritualistic. They move in from the forest and wait until all
the humans have gone into the cave for the night. The
boy notices that the same wolf is the first one to get to
the good scraps. It doesn’t immediately run off when it
sees the boy.
Domestic dogs wouldn’t appear on the scene for
another 5,000 years….
19
20,000 years ago,
a boy looked out of a cave …
20
The Family Canidae
21
Jackal
(Black-backed jackal)
Members
of the
Family
Canidae
Fox
(Kit fox, Red fox)
Wolf
(Gray wolf)
African wild
dog
22
Domestic dogs look like they are more
closely related to wolves than other
canids.
Siberian husky
(domestic dog)
Gray wolf
Coyote
23
Of course, looks can be deceiving!
Gray wolf
Domestic dog
(Lhasa apso)
Phylogenetic analyses are more convincing.
24
Phylogenetic Analysis
• Phylogenies can be based on
morphology
– Similarity of many morphological
characteristics are used (color, size,
structure, etc.)
• Most recent phylogenies are based on
molecular similarities
– E.g., similarities of mitochondrial DNA
(mtDNA) sequences
– More similarities (i.e., fewer dissimilarities) =
25
a closer relationship
Phylogeny
The study of evolutionary relationships
– Think of it as a family tree
A
B
C
D Recent
time
Species A, B, C & D all
exist in modern times
Past26
time
Phylogeny
The study of evolutionary relationships
– Think of it as a family tree
Sp A
Sp B
Sp C
Sp D
Unique
ancestor
of D only
Common ancestor
of both C & D, but
not A & B
Common ancestor
of A, B, C & D
27
CQ#1: Which statement can be made
about this phylogeny?
A. Species A, B, and C are extinct.
B. Species C & D shared a common ancestor
more recently than B & D.
C. Species D will display the most advanced
morphological characteristics.
D. Species D is most closely related to Species
A.
E. Species D evolved from Species C.
Sp A
Sp B
Sp C Sp D
28
CQ#1: Which statement can be made
about this phylogeny?
A. Species A, B, and C are extinct. – ALL MODERN
B. Species C & D shared a common ancestor
more recently than B & D.
C. Species D will display the most advanced
morphological characteristics. – Just different
D. Species D is most closely related to Species A. –
Just, no.
E. Species D evolved from Species C. – common
ancestor only
Sp A
Sp B
Sp C Sp D
29
Cladograms are another way to
look at phylogenies
30
Species A
Species B
Species C
Species D
Species E
Species F
Species A & B are more similar to each other than they are to any other
species
Species A-D are more similar to each other than they are to either species
E or F
Species C & D shared a common ancestor in more recent times than the
31
shared common ancestor of A-D
In Groups: Discuss relationships
and create a cladogram for:
Domestic dog
Fox
Wolf
Jackal
32
CQ#2: Which of the following most
closely resembles your cladogram?
A.
Dog
B.
Wolf
C.
Dog
Jackal
Wolf
Jackal
Fox
Fox
Dog
D.
Dog
Wolf
Jackal
Wolf
Fox
Jackal
Fox
33
E. Wow, mine looks like none of these
Canid Phylogeny
34
CQ#3: According to the molecular
evidence shown in the cladogram, which
statement is most true?
A. Foxes and wolves are closely
related.
B. Domestic dogs and wolves are
as closely related to each other
as they are to coyotes.
C. Out of the canids tested, a Gray
wolf shares the most recent
ancestor of the domestic dog.
D. The domestic dog is the most
evolved of the canids.
35
CQ#3: According to the molecular
evidence shown in the cladogram, which
statement is most true?
A. Foxes and wolves are closely
related. –
B. Domestic dogs and wolves are
as closely related to each other
as they are to coyotes.
C. Out of the canids tested, a Gray
wolf shares the most recent
ancestor of the domestic dog.
D. The domestic dog is the most
evolved of the canids.
36
Comparing wolves with dogs
• Morphological comparisons (examples)
• Dogs tend to have curled tails, wolves
have straight tails.
• Dogs tend to have smooth short coats.
• Skull shape differs.
• Molecular comparisons
• Gray wolves and dogs differ by no more
than 0.2% in their mtDNA sequence.
• In contrast, gray wolves and coyotes differ
by at least 4%.
37
How did dogs evolve
from wolves?
Competing hypotheses
– Ancestral wolf pups were domesticated
intentionally by early humans – Artificial
selection.
– Ancestral wolf populations experienced
natural selection forces that favored doglike characteristics.
38
Hypotheses 1 – Artificial Selection
• Arguments for
– It makes intuitive sense that ancestral
wolves could be domesticated easily since
they are so dog-like. Early humans would
have intentionally bred ancestral wolves.
• Arguments against
– Why would any human want to deal with an
animal that avoids humans?
– Modern wolves can not be “domesticated”
by training alone. It takes intensive and
sophisticated selective breeding.
39
Hypothesis 2 – Natural Selection
• Canids are very resourceful & would have
found human waste piles good foraging –
wolves were living close to humans.
• Wolves are shy, skittish animals – only
“adventurous” wolves would have stayed
close to the waste piles while humans
were around.
• The “adventurous” wolves were the best
fed and hence had high fitness.
40
CQ#4: What is fitness in the evolutionary
sense?
A. Being the strongest and most able to
get food.
B. Being able to survive and reproduce
more successfully than others.
C. Being the most aggressive and
fending off potential predators.
D. Being the smartest and remembering
where the best food resources are.
41
CQ#4: What is fitness in the evolutionary
sense?
A. Being the strongest and most able to
get food.
B. Being able to survive and reproduce
more successfully than others.
C. Being the most aggressive and
fending off potential predators.
D. Being the smartest and remembering
where the best food resources are.
42
CQ#5: What characteristic is being
selected for in the ancestral wolf
population under Hypothesis 2?
A. Ability to interact with humans.
B. Capability of eating human waste.
C. Behaviors that lead to tolerance of
humans being around.
D. Inability to run away from humans.
43
CQ#5: What characteristic is being
selected for in the ancestral wolf
population under Hypothesis 2?
A. Ability to interact with humans.
B. Capability of eating human waste.
C. Behaviors that lead to tolerance of
humans being around.
D. Inability to run away from humans.
44
A Plausible Series of Events
• Those ancestral wolves that tended to
tolerate humans would have had the
best access to high-quality food
(scraps).
• Canids likely would have protected
their scrap piles from other invading
animals and possibly even strange
humans.
45
What did humans give dogs?
• Easy access to high-quality food.
• A safe “home” to raise pups.
• What else…
46
CQ#6: What did the first "dogs" give
humans that is the most significant
in evolutionary terms?
A. An efficient garbage disposal.
B. An affectionate pet.
C. An early warning system that
someone or something was
approaching.
47
CQ#6: What did the first "dogs" give
humans that is the most significant
in evolutionary terms?
A. An efficient garbage disposal.
B. An affectionate pet.
C. An early warning system that
someone or something was
approaching.
48
Epilogue
• Molecular data suggest multiple
“domestications” in multiple areas.
• Canids artificially selected for tameness
also showed characteristics common to
domestic dogs:
– Curled tails
– Mottled coats
– Floppy ears
49
Cladogram Activity
• If you don’t finish in class, it will be
homework due NEXT time.
50