Transcript Tree-Thinking_Modules_&_Lab_Exercises_files/Tree thinking farm

Breeding Belayev’s Pets
by J. Phil Gibson, University of Oklahoma
Objectives:
– Understand how artificial selection supports
Darwin’s Theory of Evolution by Natural Selection
– Understand how artificial selection can change
characteristics of a breeding population.
– Investigate changes that occur as a result of
domestication.
CQ#1
Which of these forms of data did Darwin
not use in developing his Theory of
Natural Selection?
a. fossils
b. domesticated species
c. Mendelian genetics
d. structural homology
e. Darwin used all of these forms of data
CQ#2
Domestication involves selectively breeding
for . . .
a. many separate, genetically-based traits
specifically chosen by the breeder.
b.genetically-based traits that arise at random
due to the species’ need for those traits.
c. some genetically-based traits and
unpredictable changes in other traits that
were not specifically chosen.
d.genetically-based and environmentally
caused traits.
Darwin’s Data
In addition to examples of adaptation,
structural homology, the fossil record, and
biogeography, Darwin used domesticated
species as support for his theory evolution.
Why do you think domesticated species would
be an important part of his theory?
4
Darwin’s & Inheritance
Because Mendel’s work was not yet known and
discovery of DNA was almost a century in the
future, domesticated species provided the only
information on heritable traits and how breeders
can change in a lineage over time, a process
Darwin called ARTIFICIAL SELECTION which is
similar to NATURAL SELECTION.
5
Artificial Selection
Pigeons, cattle, and other domesticated species
provided Darwin with examples of how breeders
choose individuals with particular traits and by
allowing those individuals to breed, desired parental
traits become more common and the population
changes over time.
Darwin’s Observations
In addition to traits intentionally chosen by
breeders, Darwin noted this observation
in The Origin of Species, “. . . not a
single domestic animal can be named
which has not in some country
developed drooping ears.”
Darwin’s Observations
Not only drooping ears, but other unexpected
traits also appear in domesticated species
including piebald coloration (most
domesticated mammals), wavy hair (sheep,
poodles, horses, pigs, goats, mice, guinea
pigs), rolled tails (dogs, pigs), shorter tails
(dogs, cats, sheep), and changes in
reproductive cycles (domesticated mammals
excluding sheep).
What could this mean?
Dogs, the first domesticated animal
species, were domesticated from
gray wolves in Southwest Asia over
15,000 years ago.
Canis lupus
Canis lupus familiaris
9
Two questions about dogs in
particular and domestication in
general have interested
biologists for many years.
1. What changes occur during
domestication?
2. How quickly could
domestication occurr?
How would you approach this
Dogs of King Antef from Egyptian problem scientifically ?
relief (2323 BC. to 2134 BC).
10
The Farm-Fox Experiment
In 1959, Dr. Dimitry K. Belyaev, Director of the
Institute of Cytology and Genetics in the
U.S.S.R. began investigating the genetics of
dog domestication by selectively breeding
another canine, silver foxes, from local fur
production farms.
Vulpes vulpes
CQ#3
Dr. Belyaev hypothesized that variation in tameness
is linked to genes. Domestication is a strong
selective pressure that will change tameness of a
fox population over time.
How long do you think it will take for a population to
become “tame” or considered domesticated?
a. Very quickly, just a few generations
b. Moderate time, a slow start but quickly after the
first generations of breeding.
c. Fairly slow, a gradual change over many
generations
The Farm-Fox Experiment
Procedure
• Fox pups (called kits) were scored for tameness
and assigned to classes:
– Class 3: flee or aggressive response to experimenter
– Class 2: allow petting but no emotional response to
experimenter
– Class 1: friendly to experimenter (wag tail, whine, etc.)
• Bred the most friendly Elite Class 1 (E1) foxes
over many generations.
What specific changes would you expect to observe
over time as the experiment proceeded?
Farm-Fox Experiment Results
The number of E1 foxes increased in frequency
and showed significant increases in “dog-like”
behavior (docile, eager to please, lick hands,
compete for attention) in relatively few
generations.
Generation
%1E foxes
10
18
20
35
35
70-80
Farm-Fox Experiment Results
But, there were other changes as well.
Generation
Observations
2
decreased aggressive response
4
tail wagging, petting allowed
6
friendly kits follow and lick humans
9
floppy ears, piebald fur, forehead star
appear
13
tail curls
15
shorter tail, fewer vertebrae
The Farm-Fox Experiment
17
CQ#4
The results so far indicate. . .
a. domestication is a slow process.
b. selecting on one trait can lead to changes in
another, unselected trait.
c. fox domestication has little to do with dog
domestication.
d. domestication proceeds by changing one trait at a
time.
e. None of the above.
Farm-Fox Experiment Data
In addition to appearance, other changes occurred. The time when different
maturation events occur in dogs and foxes are show below. Complete the
figure for when you think these events should occur in domesticated foxes.
DAYS
7 8 9 10 11 12 13 14 15 16 17 18 19
WEEKS
4 6 8 10 12
DOGS
WILD
FOXES
DOMESTICATED
FOXES
eyes fully open
response
to sound
window of
socialization
The Farm-Fox Experiment
Having seen the changes produced by selective
breeding, what should the researchers study next to
support the idea that artificial selection for tameness
has produced an evolutionary change in the fox
population?
Think of a follow-up research question, develop an
hypothesis, and design an experiment you would
conduct to test it.
CQ#5
Studies have found changes in hormone levels
such as corticosteroids rise at 2-4 months in wild
foxes, but come much later in domesticated fox.
If all of the observed these changes are
genetically based, what would you expect if they
bred for aggressive instead of docile behavior.
a.aggression should decrease in those lineages
b. aggression should increase in those lineages
c. no changes should occur in those lineages
CQ#6
As predicted, fox lineages bred for aggression
became more so. Comparisons of the docile and
aggressive foxes have identified multiple genetic
differences between them. This indicates that . . .
a. domestication involves relatively few genes.
b. domestication affect genes for traits being
selected as well as other traits.
c. domestication changes only those traits selected.
d. domestication is basically the same as training an
animal to behave.
Epilogue
Genetic analysis of the aggressive and
domesticated silver fox lineages have
identified two regions that are distinct
between them.
Studies of these regions and the genome of
other domesticated species will not only
provide deeper insights into the genetic
changes caused by domestication but
may also provide insights into changes
that occurred in human evolution as well.
23
CQ#7
Suppose researchers were to take a kit from an aggressive
mother fox and have it nursed by a docile mother fox
What would you predict would happen?
a. The kit would become docile due to hormones in her
milk.
b. The kit would cause the docile mother to become
aggressive.
c. The kit would be more easily trained than if the
aggressive mother raised it.
d. The kit would mature to become an aggressive adult.
e. No predictions can be made because breeding is
unpredictable.
Deeper Thinking
You have rescued a puppy from a local animal shelter. As it
grows, you and your friends make different guesses
about what breeds its parents were.
One day you notice a web site that
announces it can tell you the
breeds of dog produced your
lovable mutt simply by sending
them a swab of the cells from the
inside of your puppy’s mouth.
Using accurate terminology, describe or diagram how this
company’s offer could possibly work.