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Dive into the origins of domestic dogs and how natural and artificial selection have influenced speciation within the Canidae family. Understand the relationship between wolves, foxes, and domestic dogs through genetic and morphological analyses. Explore competing hypotheses on how dogs evolved from wolves, considering the roles of intentional domestication and natural selection. Join us on a journey 20,000 years back when the bond between humans and canids likely began.
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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.
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?
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….
20,000 years ago, a boy looked out of a cave …
Jackal (Black-backed jackal) Fox (Kit fox, Red fox) Wolf (Gray wolf) African wild dog Members of the Family Canidae
Coyote Domestic dogs look like they are more closely related to wolves than other canids. Siberian husky (domestic dog) Gray wolf
Domestic dog (Lhasa apso) Gray wolf Of course, looks can be deceiving! Phylogenetic analyses are more convincing.
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 • DNA • More similarities (i.e., fewer dissimilarities) = a closer relationship
Phylogeny A B C D Recent time Past time The study of evolutionary relationships • Think of it as a family tree Species A, B, C & D all exist in modern times
Phylogeny Sp A Sp B Sp C Sp D 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
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 shared common ancestor of A-D
In Groups: Discuss relationships and create a cladogram for: Fox Domestic dog Wolf Jackal
CQ#2: Which of the following most closely resembles your cladogram? Dog Dog B. A. Wolf Wolf Jackal Jackal Fox Fox Dog C. D. Dog Wolf Jackal Jackal Wolf Fox Fox E. Wow, mine looks like none of these
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%.
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.
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.
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.
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.
