Download Speciation: forming a new species

SPECIATION
CH. 16-3 PP. 326-330
FORMING A NEW
SPECIES
Speciation: forming a new species
FORMING A NEW
SPECIES
Speciation: forming a new species
Species: a group of organisms that
can mate and produce fertile
offspring
FORMING A NEW
SPECIES
Speciation: forming a new species
Species: a group of organisms that can
mate and produce fertile offspring
1. same number of chromosomes
2. similar morphology (body
structure)
DISRUPTIVE
SELECTION
Divergent evolution that most likely results
in two new species
MECHANISMS
• Allopatric speciation
caused by geographic
isolation
MECHANISMS
• Allopatric speciation
caused by geographic
isolation
• physical separation of
organisms (mountain,
river forms etc)
MECHANISMS CONT.
• Sympatric Speciation due
to reproductive isolation
MECHANISMS CONT.
• Sympatric Speciation due
to reproductive isolation
• Live in the same area
• Barriers to successful
breeding
MECHANISMS CONT.
Two types of Sympatric Speciation
Barriers
• Prezygotic: before fertilization (i.e
breeding times, mating calls etc.)
MECHANISMS CONT.
Two types of Sympatric Speciation
Barriers
• Prezygotic: before fertilization (i.e
breeding times, mating calls etc.)
• Postzygotic: after fertilizationinfertile offspring (chromosome #
doesn’t add up)
RATES OF
SPECIATION
• Gradualism: slow divergence (small
changes)
• Punctuated equilibrium: sudden shift in
form (irregular)
PRE OR
POSTZYGOTIC?
• offspring die young when two species of
salamanders mate – they do not make it to
maturity
PRE OR
POSTZYGOTIC?
• Two different species of birds have different
mating calls so they cannot recognize each
other as mates
PRE OR
POSTZYGOTIC?
• garter snakes that live in water and one on
land cannot mate although they live in the
same geographic area
PRE OR
POSTZYGOTIC?
• mules are produced by mating a horse and
a donkey, but mules are sterile and cannot
breed
PRE OR
POSTZYGOTIC?
• if gametes of red and purple sea urchins do
not fuse, there will be no zygote produced
PRE OR
POSTZYGOTIC?
• although some strains of cultivated rice can
be cross-mated, after a few generations,
sterile offspring are created