Transcript dog evolution

Not Necessarily on Purpose:
Domestication and Speciation
in the Canidae Family
Tom Horvath
Department of Biology
SUNY College at Oneonta
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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.
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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?
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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….
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20,000 years ago,
a boy looked out of a cave …
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The Family Canidae
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Jackal
(Black-backed jackal)
Members
of the
Family
Canidae
Fox
(Kit fox, Red fox)
Wolf
(Gray wolf)
African wild
dog
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Domestic dogs look like they are more
closely related to wolves than other
canids.
Siberian husky
(domestic dog)
Gray wolf
Coyote
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Of course, looks can be deceiving!
Gray wolf
Domestic dog
(Lhasa apso)
Phylogenetic analyses are more convincing.
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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) =
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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
Past11
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
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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
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Cladograms are another way to
look at phylogenies
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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
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shared common ancestor of A-D
In Groups: Discuss relationships
and create a cladogram for:
Domestic dog
Fox
Wolf
Jackal
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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
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E. Wow, mine looks like none of these
Canid Phylogeny
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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 is the most likely ancestor
of the domestic dog.
D. The domestic dog is the most
evolved of the canids.
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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%.
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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.
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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.
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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.
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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.
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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.
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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.
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What did humans give dogs?
• Easy access to high-quality food.
• A safe “home” to raise pups.
• What else…
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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.
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Phylogeny of Domestic Dog
Breeds – Result of Artificial
Selection
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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
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