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

Tom Horvath Department of Biology SUNY College at Oneonta

1

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.

2

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?

3

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….

4

20,000 years ago, a boy looked out of a cave …

5

The Family Canidae

6

Jackal (Black-backed jackal)

Members of the Family Canidae

Fox (Kit fox, Red fox) Wolf (Gray wolf) African wild dog

7

Domestic dogs look like they are more closely related to wolves than other canids.

Gray wolf Siberian husky (domestic dog) Coyote 8

Of course, looks can be deceiving!

Gray wolf Domestic dog (Lhasa apso)

Phylogenetic analyses are more convincing.

9

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

10

A

Phylogeny

The study of evolutionary relationships

–

Think of it as a family tree B C D Recent time Species A, B, C & D all exist in modern times Past

11

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

12

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

13

Cladograms are another way to look at phylogenies

14

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

15

shared common ancestor of A-D

In Groups: Discuss relationships and create a cladogram for:

Domestic dog Fox Wolf Jackal

16

A.

CQ#2: Which of the following most closely resembles your cladogram?

Dog B.

Dog Wolf Wolf Jackal Jackal Fox Fox C.

D.

Dog Jackal Dog Wolf Wolf Fox Jackal Fox

17

E. Wow, mine looks like none of these

Canid Phylogeny

18

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.

19

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%.

20

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.

21

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.

22

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.

23

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.

24

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.

25

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.

26

What did humans give dogs?

• • •

Easy access to high-quality food.

A safe “home” to raise pups.

What else…

27

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.

28

Phylogeny of Domestic Dog Breeds – Result of Artificial Selection

29

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

30