Process of Speciation

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

3
Intro to Speciation

• Therefore individuals of the same species share a
  common gene pool.

4
Intro to Speciation

• As genetic change
• occurs in one individual,
• it can spread through
• the population via
• its offspring.

5
Intro to Speciation

• If this change increases fitness it will soon
  be found in many within the population.

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 wont berecognized bythose 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
Meadowlarks
Behavioral Isolation

• Western Eastern

12
Behavioral Isolation

• Difference in
• courtship rituals

Western and Eastern Meadowlark (Different mating
songs)
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 MacGregors 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).
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

16
Geographic Isolation

• Another Example of Speciation due to Geographic
  Isolation
• (Colorado River 10,000 years ago)

Kaibab Squirrel (Sciurus aberti
kaibabensis)
Abert Squirrel (Sciurus aberti)
Grand Canyon
17
Geographic Isolation

• 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 iguanaand 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

20
Temporal Isolation

• If one species reproduces in the spring, while
  the other reproduces in the fall, the two species
  arent able to breed

21
Temporal Isolation

• Example
• 3 similar species of
• orchid in same forest
• release pollen on different days (can
  not pollinate one another)

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
Darwins Discovery

• Galapagos Island Finches

25
Darwins 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

26
Darwins Discovery

• He then hypothesized
• They had descended from a common ancestor.
• Natural selection shaped the beaks as they
  adapted to eat different foods

27
Concept Map
Reproductive Isolation
results from
Isolating mechanisms
which include
produced by
produced by
produced by
which result in
Independentlyevolving populations
which result in
Formation ofnew 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 Grants 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

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

Peter and Rosemary Grant (Princeton
University)
31
Speciation of Finches in the Galapagos Islands
Galapagos Islands
South America
a) Founders Arrive
b) Separation of Populations
c) Changes in the Gene Pool
d) Reproductive Isolation
e) Ecological Competition
f) Continued Evolution
32
Follow these Steps as Review of Speciation in
Darwins 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