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Speciation
Outline
• Marshmallow Challenge
• Speciation
Marshmallow Challenge
• In science, scientists often work as a team
– Able to work with all different people
– To do research
– Publish papers
This activity will test your team-working skills
Marshmallow Challenge
• Purpose: build the tallest freestanding
structure using the materials provided in 15
minutes
• Materials:
– 20 sticks of pasta
– 1 meter of tape
– 1 marshmallow
Condition: the marshmallow has to be at the very top
Species?
• What is a species?
– Difficult to define
– Organisms that can interbreed under natural
conditions and produce viable offspring
Are lions and tigers the same species? Why?
Speciation
• Formation of new species
• Modes:
– Reproductive isolation
– Allopatric speciation
– Sympatric speciation
Mechanisms of Reproductive
Isolation
•
•
Must evolve to become reproductive
isolated from the original population
Reproductive isolating mechanism:
– Any factor that prevents two populations
from interbreeding when living in the same
region
1) Prezygotic mechanisms
2) Postzygotic mechanisms
Prezygotic Mechanisms
•
1)
2)
3)
4)
5)
Prevent fertilization and zygote formation
Behavioural
Temporal
Ecological
Mechanical
Gametic
• Behavioural – the behaviours of organisms
are not recognized by each other
– E.g. mating calls of frogs
• Temporal – breed at different times of the
year
– E.g. flowering times of certain plants
• Ecological – species are physically
separated thus occupy different areas
– E.g. birds that prefer higher or lower
elevations
• Mechanical – incompatible reproductive
organs
– E.g. different species of damselflies have
uniquely shaped genitalia
• Gametic – gametes do not recognize each
other
– E.g. sperms of clams will not fertilize sea
cucumbers’ eggs
Postzygotic Mechanisms
•
Prevent fertilized egg from growing into a
viable and reproducing adult
1) Zygotic mortality
2) Hybrid inviability
3) Hybrid infertility
• Zygotic mortality – after fertilization, zygote
dies
– Zygote of sheep and goat is not viable
• Hybrid inviability – hybrid develops but
dies before birth or cannot survive until
maturity
– Tigers and leopard hybrids ends in
miscarriage or stillborn
• Hybrid infertility – hybrid is healthy but
infertile
– Mules are infertile
Examples of hybrids that are fertile!
•
•
•
•
Wholphin
Grizzly-polar bear
Cama
Coywolf
Allopatric Speciation
• Formation of new species due to long
period of geographic isolation
• Gradually become less and less alike
– No genetic information exchange
– No shared mutations
– Experience different natural selection
Examples
• Finches on Galapagos Islands
• Asian elephants – has 4 distinct
subspecies
Sympatric Speciation
• Evolution of populations into separate
species in the same geographic area
• Example:
– Hawthorn flies lay eggs in the fruits of
hawthorn trees
– After apple trees were introduced, some of
the flies would lay eggs in the apples
– Today, the species are now consist of two
distinct populations
Divergent Evolution
• Evolution of a group into many forms
• All come from a single common ancestor
• Rodents:
– Deer mouse
– Flying squirrel
– Porcupine
– beaver
Convergent evolution
• Evolution of similar traits in
distantly related species
• Can be predicted like divergent
evolution
• Examples:
– Euphorbia and cacti evolved similar
features in response to hot, dry
environments
– Sharks and dolphins evolved similar
stream-lined bodies
Coevolution
• One species evolves in response to the
evolution of another species
• Example: orchid and moth
– Orchid require moth to pollinate the flowers
– Moth depends on orchid for nectar
– Over time, orchid evolved extremely long
tubes and moth developed long tongue
– Moth will spend more time obtaining nectar
and thus making them more likely to pick up
pollen
Figure 8 on pg. 344
Homework Questions
• Section 7.4: #4-8
• Section 8.2: #1-5
Exit Card
• Come up with at least one
question that you are not very
clear about on speciation. Please
make the question and the writing
as clear as possible.