Download Lesson 2

Speciation
Objectives:
1. Define the term speciation and explain what it means.
2. Describe two different modes of speciation.
3. Explain what extinction is and how it happens.
Other Mechanisms that Drive
Evolution
• Sexual Selection: the process
by which a trait that enables
an organism to acquire more
mates becomes more
common.
• Males compete for females
(combat)
• Females chose males
(desirable traits)
7D Variation – What is a species?
How many different types of living things are there on Earth?
Scientists have identified almost 2 million different types of living things.
Many more are yet to be discovered and scientists estimate there
could be up to 30 million different types of living things!
Each different type of living thing is called a species.
Do members of the same species look exactly the same?
7D Variation – Similar but different
A species is a group of living things with similar features.
• Members of the same species can breed
together to produce fertile offspring.
• Members of different species cannot
interbreed under normal conditions.
– We say they are reproductively isolated from each
other.
7D Variation – Similar but different
Name 5 ways in which these dogs are similar.
Name 5 ways in which these dogs are different.
7D Variation – What is variation?
Differences between members of the same species
are called variation.
7D Variation – Causes of variation
Variation is caused by environmental or
inherited factors.
Which type of variation is described by each definition?
A
inherited
This type of variation is passed on
in genes from parent to offspring.
B
environmental
This type of variation is influenced
by living conditions and
surroundings.
7D Variation – Environmental factors
Environmental variation is caused by differences in
living conditions and surroundings.
Climate and food supply are environmental factors that influence all living
things.
How might these environmental factors cause variation?
Invisible Differences...
• Disease resistance: Some fruit are resistant to
certain diseases.
– Green Anjou pears are more resistant to a disease
called fireblight.
• If they were attacked by this disease they would be less
likely to get it.
• BUT ... You can’t tell this just by looking at the
pears can you???
Why do different organisms live in
different environments??
• Different organisms are adapted to live in certain
environments.
• An adaptation is a trait or characteristic that
enables an organism to survive.
• These adaptations are then passed on to their
offspring.
Overtime, so many adaptations or differences may
accumulate that individuals can no longer interbreed
and have to be considered a difference species.
Speciation
• A new species is formed when two
populations of plants or animals
accumulate so many genetic changes
(mutations, adaptations) that they
cannot interbreed and produce fertile
offspring.
Modes of Speciation…
• These processes all include the evolution of
distinct features that isolate the new species
reproductively and as a result genetically fro
the original species.
1. Reproductive isolation
2. Allopatric Speciation
3. Sympatric Speciation
1. Reproductive Isolation
Individuals are prevented from breeding together
because of behavioural, structural or biochemical
traits.
- Behavioural: Different courtship displays, different
breeding seasons or different habitats
- Structural: Different/Incompatible
genitalia
- Biochemical: Male gamete may not recognize female
gamete.
Pre and Post zygotic mechanisms
• Prezygotic mechanisms prevent fertilization and
zygote formation.
– Behaviour isolation
– Temporal isolation
– Ecological or Geographical isolation
– Mechanical or Gametic isolation
• Postzygotic mechanisms prevent a fertilized egg
from developing.
– Hybrid in viability
– Hybrid sterility or breakdown
2. Allopatric Speciation
A new species develops after being geographically
separated from the original population.
a) They can no longer exchange genetic information
b) Any mutation that arises in one population is not
shared with the other
c) Differences in environments may lead to
differences in natural selection
Other differences such as courtship displays and
breeding season may evolve.
The scene: a population of wild fruit flies
minding its own business on several bunches
of rotting bananas, cheerfully laying their
eggs
in the
mushy
Disaster
strikes:
A fruit...
hurricane washes the
bananas and the immature fruit flies they
contain out to sea. The banana bunch
eventually washes up on an island off the coast
of the mainland. The fruit flies mature and
emerge from their slimy nursery onto the
lonely
island. Thediverge:
two portions
of theconditions
The populations
Ecological
population,
mainlandonand
now
are slightly different
theisland,
island,are
and
thetoo
far
apart
for gene evolves
flow to unite
At this
island
population
underthem.
different
point,
speciation
has
notexperiences
occurred —different
any fruit
selective
pressures
and
So we meet
again: When
another storm
flies
thatevents
got back
to the
the mainland
mainland could mate
random
reintroduces
thethan
island
flies to the population
mainland,
and
produce
healthy
offspring
with
the
does.will
Morphology,
and
they
not readilyfood
matepreferences,
with the mainland
mainland
flies.
courtship
change over
the course
of
flies
since displays
they've evolved
different
courtship
many generations
natural
selection.
behaviors.
The fewofthat
do mate
with the
mainland flies, produce inviable eggs because
of other genetic differences between the two
populations. The lineage has split now that
genes cannot flow between the populations.
3. Sympatric Speciation..
New species are formed when individuals within
a larger population become genetically isolated.
- More common in plants than in animals.
- Can be gradual ______________
- Can be sudden such as when a mutation
affects a few individuals of a population
preventing them from mating with others.
Extinction
• Why are there fossils of organisms that don’t
exist today?
• Why do you think organisms go extinct?
• Through evolution, new species arise through
the process of speciation
– New varieties of organisms arise and thrive when
they are able to survive in an environment
• Species become extinct when they are no
longer able to survive in changing conditions
or against superior competition.
What causes extinction
• Any species that is …
– unable to survive or reproduce in its environment
• Extinction of a species may come suddenly
when an otherwise healthy species is wiped
out completely.
– Pesticides make insects food uneatable
– New predator is introduced and animal can’t
escape
– Disease wipes out species
Plenary
• 1. Explain what speciation means.
• 2. What are three different modes of
speciation?
• 3. How can individuals of a species become
reproductively isolated?
• 4. What is the difference between allopatric
speciation and sympatric speciation.
Your Task
• Read through your handout on ‘Speciation’ and
answer questions 1 to 5.
• Question to consider…
• Cheetahs have very little genetic variation from
individual to individual. Based on Darwin’s theory of
natural selection, how might this influence the
evolution of the species?
• Species with very little genetic variation have an
increased risk of becoming extinct. Why?