1. Process of Speciation
Ch 16.3

2. Intro to Speciation Recall, biologists define a species
as a group of individuals that breed
and produce fertile offspring
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3. Intro to Speciation
Therefore individuals of the same species share a common gene pool.
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4. Intro to Speciation As genetic change occurs in one individual,
it can spread through
the population via
its offspring.
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5. Intro to Speciation
If this change increases “fitness” it will soon be found in many within the population.
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6. Speciation Defined as- The formation of new species
As new species evolve, populations become reproductively isolated

7. Reproductive Isolation
Defined as-
When members of two populations cannot interbreed
* Breeding can be prevented due to changes in behavior (eating, mating rituals, timing) environment (niches, food source, geographic barriers) or mechanics (breeding, fertilization, development)

8. Isolating Mechanisms Reproductive isolation can occur as a result of:
Behavioral Isolation
Geographic Isolation
Temporal Isolation
Mechanical Isolation

9. Behavioral Isolation
Defined as- the isolating mechanism that operates through differences in courtship behavioral patterns
Different mating location, mating time, or mating rituals
If one species displays a certain courtship pattern, it won’t be recognized by those of the other species

10. Behavioral Isolation
This is the mechanism which separates wolfs from dogs, their courtship patterns are different in the wild

11. Behavioral Isolation
Meadowlarks
Western Eastern

12. (Different mating songs)
Behavioral Isolation
Difference in
courtship rituals
Western and Eastern Meadowlark
(Different mating songs)
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13. Behavioral Isolation
Different species of bowerbird construct elaborate bowers and decorate them with different colors in order to woo females. The Satin bowerbird (left) builds a channel between upright sticks, and decorates with bright blue objects, while the MacGregor’s Bowerbird (right) builds a tall tower of sticks and decorates with bits of charcoal. Evolutionary changes in mating rituals, such as bower construction, can contribute to speciation.

14. Behavioral Isolation Feeding Habits - change in food preference
Fruit flies switched from Hawthorn fruit to Apple fruit introduced from England
No gene flow occurs now because they eat, mate, and lay their eggs on different hosts (fruit).
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15. Geographic Isolation
When two populations are separated physically when their original habitat becomes divided by barriers such as rivers, mountains, or bodies of water
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16. Geographic Isolation
Another Example of Speciation due to Geographic Isolation
(Colorado River – 10,000 years ago)
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Abert Squirrel
(Sciurus aberti)
Kaibab Squirrel
(Sciurus aberti kaibabensis)
Grand Canyon

17. Geographic Isolation Island/Bodies of water
Separated the Galapagos finches, tortoises, iguanas, and other species
Island/Bodies of water

18. Geographic Isolation Speciation in action?
In the summer of 1995, at least 15 iguanas survived Hurricane Marilyn on a raft of uprooted trees.
They rode the high seas for a month before colonizing the Caribbean island, Anguilla.
Evolutionary biologists would love to know what happens next:
will the colonizing iguanas die out,
will they survive and change only slightly, or
will they become reproductively isolated from other Iguana iguana and become a new species?

19. Temporal Isolation Two or more species reproduce at different times.
The time periods could differ simply by hours, or by seasons
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20. Temporal Isolation
If one species reproduces in the spring, while the other reproduces in the fall, the two species aren’t able to breed
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21. Temporal Isolation Example: 3 similar species of orchid in same forest
release pollen on different days (can not pollinate one another)
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22. Mechanical Isolation
Deals with the actual mechanics of the reproductive organs
Occurs when there is incompatibility in structure of the male and female sex organs

23. Mechanical Isolation
Isolates species by preventing mating between two different species
Isolation also occurs when the gametes of the two species are chemically incompatible
Prevents fertilization

24. Galapagos Island Finches
Darwin’s Discovery
Galapagos Island Finches
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25. Darwin’s Discovery The finches looked so different he thought
they were blackbirds,
warblers, & other kinds
of birds.
After returning home,
an ornithologist told
him they were all
finches
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26. Darwin’s Discovery He then hypothesized:
They had descended from a common ancestor.
Natural selection shaped the beaks as they adapted to eat different foods
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27. Reproductive Isolation
Concept Map
Reproductive Isolation
results from
Isolating mechanisms
which include
Behavioral isolation
Temporal isolation
Geographic isolation
produced by
produced by
produced by
Behavioral differences
Different mating times
Physical separation
which result in
Independently evolving populations
which result in
Formation of new species

28. Testing Natural Selection in Nature
Two testable assumptions
1. Sufficient Variation among
species
2. Natural Selection due to
“fitness” of the variation
Peter and Rosemary Grant

29. Testing Natural Selection in Nature
What the Grant’s Finch
Research Showed:
There is great variation
among inheritable traits
During drought, food
becomes scarce or gone
and big beaks more likely
to survive.
Big beak birds tend to mate
with other big beak birds,
resulting in increase in average
beak size of the population
The next generation of finches
had bigger beaks than the generations
before
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30. Testing Natural Selection in Nature
After 20 years of banding
& measuring finches, the
Grants had demonstrated
that evolutionary changes
in finch beak size & shape
occur rapidly in response
to severe environmental
changes in the Galapagos
Image:
Peter and Rosemary Grant (Princeton University)

31. Speciation of Finches in the Galapagos IslandsB
South
America
a) Founders Arrive
b) Separation of Populations
c) Changes in the Gene Pool E
Speciation in the Galapagos finches occurred by:
a) Founders Arrive
A few finches travel from South America to one of the islands. There, they survive and reproduce.
b) Separation of Populations
Some birds from species A cross to a second island. The two populations no longer share a gene pool.
c) Changes in the Gene Pool
Seed sizes on the second island favor birds with larger beaks. The population on the second island evolves into a population, B, with larger beaks.
d) Reproductive Isolation
If a few population-B birds cross back to the first island, they will not mate with the birds of population-A. The gene pools are now separate. Populations A and B are separate species.
e) Ecological Competition
As species A ad B compete for seeds on the first island, they continue to evolve. A new species, C, may evolve. Some members of the original species B may travel to a new island.
f) Continued Evolution
The process continues, leading to the formation of all 13 finch species on the Galapagos. D B A C A C A B B B
d) Reproductive Isolation
e) Ecological Competition
f) Continued Evolution

32. Follow these Steps as Review of Speciation in Darwin’s Finches
1. Founders Arrive on an Island 2. Separation of Population (some birds of species A cross to another island) 3. Change in Gene Pool (natural selection causes species A & B to evolve.)
4. Reproductive Isolation (now even if species A & B appear in same locale, gene pool remains isolated) 5. Ecological Competition (increase difference as species A & B compete.) 6. Continued Evolution