Speciation

1
Speciation
2
What is a species?

• I look at the term species, as one arbitrarily
  given for the sake of convenience to a set of
  individuals closely resembling each other...."
• (Darwin, 185952)

3

• Biological Species Concept
• Dobzhansky (1937) "species are groups of
  actually or potentially interbreeding natural
  populations which are reproductively isolated
  from other such groups"

4
           
5
Speciation
gene flow between two populations is interrupted
genetic differences gradually accumulate between
the two populations as as a result of natural
selection.
The two populations eventually become very
different and cannot reproduce together even if
reunited reproductive isolation
6
How is gene flow interrupted?
7
Allopatric speciation

• Speciation due to geographical isolation between
  populations is known as
• Allopatric speciation.

8
Allopatric Speciation
A a
A a
B b
A a
A a
B b
9
Sympatric Speciation Speciation occurring
within a population as a result of behavioural,
or genetic barriers is known as sympatric
speciation.
10
Sympatric Speciation
Spartina maritima 2n122
Spartina alterniflora 2n 62
Sterile Hybrid
Spontaneous chromosome doubling
Spartina anglica
11
What keeps these populations from inbreeding
later on?
12
Reproductive isolating mechanisms

• Fertilised eggs are not formed e.g. mechanical
  problems.
• Hybrid inviability hybrids dont live to
  maturity
• Hybrid sterility hybrids fail to produce
  functional gametes

13
(No Transcript)
14
Devise a hypothesis to explain how these finch
species may have arisen by allopatric speciation.
How might you test your hypothesis? How would
you prove they are separate species? What type of
selection do you think was responsible for this
type of speciation?
15
Devise a hypothesis to explain how these two fish
species may have arisen by sympatric speciation
in the same lake. How might you test your
hypothesis? How would you prove they are separate
species? What type of selection do you think was
responsible for this type of speciation?
16
(No Transcript)
17
Edexcel Requirements

• understand that isolating mechanisms lead to the
  divergence of gene pools
• understand geographical and behavioural isolating
  mechanisms reproductive isolation
• explain the difference between sympatric and
  allopatric speciation.