Speciation, Reproductive Isolation, and Patterns of Evolution

1
Speciation, Reproductive Isolation, and
Patterns of Evolution

• AP Biology
• Evolution IV

2
Speciation

• Species a group of individuals capable of
  interbreeding
• Speciation the formation of new species (3 main
  types)
• Allopatric Speciation
• Sympatric Speciation
• Adaptive Radiation

3
Allopatric Speciation
http//www.nodvin.net/snhu/SCI219/demos/Chapter_4/
4
Allopatric Speciation

• Occurs when a population is divided by a
  geographic barrier
• Barriers mountains, rivers, regions excluding
  vital resources (water, food) areas covered with
  volcanic lava
• Interbreeding between populations not possible
  (reproductive isolation)
• Gene frequencies can diverge due to natural
  selection, mutation, and genetic drift

5
Sympatric Speciation
                                                                                                            
apple maggot flies   apples   hawthorns
6
Sympatric Speciation

• The formation of new species without the presence
  of a geographic barrier
• Occurs by one of 3 ways
• Balanced Polymorphism
• Polyploidy
• Hybridization

7
Balanced Polymorphism

• Suppose a population of insects possesses a
  polymorphism for color. Each color provides a
  camouflage to a different substrate (rock, tree
  stump, etc..).
• When not camouflaged, they are eaten
• Thus, only insects with the same color can
  associate and mate
• Similarly colored insects are reproductively
  isolatedso gene pools can diverge.

8
Polyploidy

• More than 2 sets of chromosomes found in diploid
  (2n) cells.
• Often occurs in plants (occasionally animals)
  where triploid (3n), tetraploid (4n) and higher
  chromosome numbers exist.
• Caused by nondisjunction in meiosis
• Tetraploid individuals will continue to produce
  diploid gametes making them reproductively
  isolated very quickly.

9
Hybridization

• Occurs when 2 different forms of a species mate
  and produce offspring along a geographic boundary
  called a hybrid zone.
• The genetic variation of the hybrids is greater
  than that of either parent
• This permits hybrids to adapt to environmental
  conditions beyond the range of either parent.
• Hybrids can eventually diverge from parent forms
  when faced with selective pressures

10
Adaptive Radiation
11
Adaptive Radiation

• Relatively rapid evolution of many species from a
  single ancestor.
• Ancestral species colonizes an area where diverse
  geographic or ecological conditions are available
  for colonization.
• i.e. many available ecological niches for a
  population to spread into.
• Examples Darwins Finches, Australian Marsupials

12
Patterns of Evolution

• Evolution can take place along the lines of the
  following patterns
• Divergent Evolution
• Convergent Evolution
• Parallel Evolution
• Coevolution

13
Divergent Evolution

• Describes two or more species that originate from
  a common ancestor.
• This may happen as a result of allopatric or
  sympatric speciation or by adaptive radiation

14
Convergent Evolution

• Describes two unrelated species that share
  similar traits.
• Similar traits arise because each species has
  independently adapted to a similar niche
• These traits are called Analogous Traits

15
Convergent Examples

• Sharks, porpoises, and penguins have
  torpedo-shaped bodies with peripheral fins.
  These traits arise as a result of adaptations
  each species has made to aquatic lifenot due to
  a common ancestor.
• The eyes of squids and vertebrates are physically
  and functionally similar. However they are not
  from a recent common ancestor, both evolved
  independently to perform similar functions.

16
Parallel Evolution

• Describes two related species or two related
  lineages that have made similar evolutionary
  changes after their divergence from a common
  ancestor
• Example
• Species from two groups of mammals, the marsupial
  mammals and the placental mammals, have
  independently evolved similar adaptations when
  ancestors encountered comparable environments

17
Coevolution

• Describes the evolution of one species in
  response to new adaptations that appear in
  another species
• An example evolutionary arms race between
  predators and preyor
• Plants and plant eating insects
• Pollinators and flowering plants
• Pathogens and animal immune systems