Not Necessarily on Purpose: Domestication and Speciation in the Canidae Family

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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 Whos Best Friend?

• The dog is said to be a mans (humans) best
  friend, but it could also be said that we are a
  dogs 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 groups previous days
  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 doesnt immediately run off when it sees the
  boy.
• Domestic dogs wouldnt 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) Fox (Kit fox, Red
fox) Wolf (Gray wolf) African wild dog
Members of the Family Canidae
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Domestic dogs look like they are more closely
related to wolves than other canids.
Siberian husky (domestic dog)
Gray wolf
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Of course, looks can be deceiving!
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)
  a closer relationship

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Phylogeny

• The study of evolutionary relationships
• Think of it as a family tree

Recent time Past time
Species A, B, C D all exist in modern times
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Phylogeny

• The study of evolutionary relationships
• Think of it as a family tree

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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CQ1 Which statement can be made about this
phylogeny?

• Species A, B, and C are extinct.
• Species C D shared a common ancestor more
  recently than B D.
• Species D will display the most advanced
  morphological characteristics.
• Species D is most closely related to Species A.
• 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 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 shared common ancestor of
A-D
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In Groups Discuss relationships and create a
cladogram for
Fox
Domestic dog
Jackal
Wolf
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CQ2 Which of the following most closely
resembles your cladogram?
B.
A.
C.
D.
E. Wow, mine looks like none of these
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Canid Phylogeny
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CQ3 According to the molecular evidence shown
in the cladogram, which statement is most true?

• Foxes and wolves are closely related.
• Domestic dogs and wolves are as closely related
  to each other as they are to coyotes.
• Out of the canids tested, a Gray wolf is the most
  likely ancestor of the domestic dog.
• 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 dog-like
  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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CQ4 What is fitness in the evolutionary sense?

• Being the strongest and most able to get food.
• Being able to survive and reproduce more
  successfully than others.
• Being the most aggressive and fending off
  potential predators.
• Being the smartest and remembering where the best
  food resources are.

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CQ5 What characteristic is being selected for
in the ancestral wolf population under Hypothesis
2?

• Ability to interact with humans.
• Capability of eating human waste.
• Behaviors that lead to tolerance of humans being
  around.
• 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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CQ6 What did the first "dogs" give humans that
is the most significant in evolutionary terms?

• An efficient garbage disposal.
• An affectionate pet.
• 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