15.3 Mechanisms of EVOLUTION
15.3 Speciation
The formation of a new species
What is a species?
A group of organisms with similar
characteristics capable of producing
fertile offspring
What is a species?
Members of a species share the same
gene pool (sum of all the genes + their
different forms – alleles)
Speciation
New species are formed when a population
diverges into two populations AND
Speciation
New species are formed when a population
diverges into two populations AND the gene
pools of two populations become
reproductively isolated
Speciation
New species are formed when a population
diverges into two populations AND the gene
pools of two populations become
reproductively isolated = the populations
can’t produce a fertile offsprings
Speciation
There are several different ways
speciation can occur...
Modes of Speciation
Allopatric Speciation
Peripatric Speciation
Parapatric Speciation
Sympatric Speciation
Allopatric Speciation
Is a type of geographic isolation
A population is split in two (or more) by some
kind of physical barrier (mountain, river,
wall…)
Allopatric Speciation
The separated populations undergo changes in
their genes as they begin to adapt to different
environments or as they undergo mutations.
Allopatric Speciation
After that time they are no longer
capable of interbreeding (exchanging the
genes)
EXAMPLE 1 – Allopatric Speciation
A population of wild fruit flies minding its own
business on several bunches of rotting
bananas. They also lay eggs inside of bananas.
EXAMPLE 1 – Allopatric Speciation
A hurricane washes the bananas and the fruit
flies’ eggs out to sea. The bananas eventually
wash up on an island off the coast of the
mainland
EXAMPLE 1 – Allopatric Speciation
The fruit flies mature (eggs became flies) and
emerge onto the lonely island. The two portions
of the population, mainland and island, are now
too far apart for gene flow to unite them.
EXAMPLE 1 – Allopatric Speciation
At this point, speciation has not occurred yet
— any fruit flies that would fly back to the
mainland could mate and produce healthy
offspring with the mainland flies.
EXAMPLE 1 – Allopatric Speciation
The populations diverge: Ecological conditions
are slightly different on the island, and the
island population evolves differently than the
mainland population does.
EXAMPLE 1 – Allopatric Speciation
Morphology (eye color), food preferences, and
mating behaviours change over the course of
many generations of natural selection
EXAMPLE 1 – Allopatric Speciation
When another storm reintroduces the island flies to
the mainland, they will not be able to mate with
the mainland flies since they’ve evolved different
mating behaviours.
EXAMPLE 1 – Allopatric Speciation
The flies’ lineages has split now that genes
cannot flow between the populations
EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
Darwin thought that a
long time ago there
must have been a
common ancestor to
the finch species.
EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
As the Galapagos
islands were formed,
the common ancestor
slowly dispersed and
broke away from one
another.
EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
Genetic variations
amongst the finches
were then selected
for by the
environment (natural
selection).
EXAMPLE 2 – Allopatric Speciation
Darwin’s Finches
This resulted in the
formation of new
species on each
island
EXAMPLE 3 – Allopatric Speciation
Blue headed wrasse and Cortez Rainbow
wrasse
EXAMPLE 3 – Allopatric Speciation
Blue headed wrasse and Cortez Rainbow
wrasse
Original population was split by the formation of
isthmus of Panama about 3.5 million years ago
EXAMPLE 3 – Allopatric Speciation
Blue headed wrasse and Cortez Rainbow
wrasse
Since that time, genetic changes happened in the both
populations. These changes led to creation of different
species
EXAMPLE 4 – Allopatric Speciation
Hawaiian honeycreepers
Very similar to Galapagos’ finches
EXAMPLE 4 – Allopatric Speciation
Hawaiian honeycreepers
On each island of Hawaii, we can find different species of
honeycreeper
EXAMPLE 4 – Allopatric Speciation
Hawaiian honeycreepers
It is thought that they all descended from a single
species of honeycreeper
EXAMPLE 4 – Allopatric Speciation
Hawaiian honeycreepers
Peripatric Speciation
a special version of the allopatric
speciation
- It happens when one of the isolated
populations has very few individuals
- genetic drift (the founder effect) plays
a major role in this speciation
Peripatric Speciation
A population of wild fruit flies minding its own business on
several bunches of rotting bananas also laying eggs inside
of bananas.
Peripatric Speciation
A hurricane washes the bananas and the fruit flies’ eggs out
to sea. The bananas eventually wash up on an island off
the coast of the mainland
Peripatric Speciation
But only a few eggs have survived the journey to end up
colonizing the island.
Peripatric Speciation
These few survivors just by chance carry some genes that
are very rare in the mainland population.
Peripatric Speciation
One of these rare genes causes a slight variation in the
mating behaviour and changes in sexual organs.
(REMEMBER? it’s an example of the founder effect)
Peripatric Speciation
After a few generations, the entire island population ends up
having these rare genes.
Peripatric Speciation
As the island population grows, flies experience natural
selection that favours individuals better suited to the
reproductive behaviour, climate and food of the island.
Peripatric Speciation
After some generations, the island flies become isolated
from the mainland flies.
Peripatric speciation has occurred
Peripatric vs Allopatric
Speciation
WHAT IS THE DIFFERENCE
BETWEEN THEM?
Peripatric vs Allopatric
Speciation
It is the size of the
populations involved!
Peripatric vs Allopatric Speciation
In allopatric speciation, a population is separated into two
relatively large independent populations.
In peripatric speciation, only a small fraction of the original
population becomes geographically isolated.
Parapatric Speciation
There is no specific barrier (mountain, river…) to gene
flow, but the population does not mate randomly
Parapatric Speciation
Individuals are more likely to mate with their geographic
neighbours than with individuals in a different part of
the population’s area
Parapatric Speciation
The two species may come in contact from time to time but
(after some time), species can no longer produce
offspring together anymore
EXAMPLE 1 – parapatric Speciation
A grass species
Anthoxanthum odoratum
EXAMPLE 1 – parapatric Speciation
Some of these plants live near mines where the soil has
become contaminated with heavy metals.
EXAMPLE 1 – parapatric Speciation
Some plants around the mines have experienced natural
selection and are now tolerant of heavy metals.
EXAMPLE 1 – parapatric Speciation
The neighbouring plants that don’t live in polluted soil have
not experienced natural selection for this trait (they have
NO tolerance of heavy metals)
EXAMPLE 1 – parapatric Speciation
Both plants are close enough that they could fertilize each
other (mate with each other)
EXAMPLE 1 – parapatric Speciation
However, the two types of plants have evolved different
flowering times. This change is the first step in cutting off
gene flow between the two groups = SPECIATION
Sympatric Speciation
In sympatric speciation, species diverge while inhabiting the
same place.
Sympatric Speciation
It does not require large area to reduce gene flow between
parts of a population
Example of Sympatric Speciation
200 years ago, the ancestors of apple maggot flies laid their
eggs only on hawthorns
Maggots
Hawthorns
Example of Sympatric Speciation
but today, these flies lay eggs on hawthorns
and domestic apples (which were
introduced to America by immigrants)
Hawthorns
Apples
Maggots
Example of Sympatric Speciation
Females generally choose to lay their eggs on the type of
fruit they grew up in, and males tend to look for mates
on the type of fruit they grew up in.
Example of Sympatric Speciation
So hawthorn flies generally end up mating
with other hawthorn flies
+
Hawthorns
Hawthorns
Example of Sympatric Speciation
and apple flies generally end up mating with
other apple flies.
+
Apples
Apples
Example of Sympatric Speciation
Hawthorn flies and apple
flies never mate together
+
Hawthorns
Apples
Example of Sympatric Speciation
This means that gene flow between parts of
the population that mate on different types
of fruit is reduced.
+
Hawthorns
Apples
Example of Sympatric Speciation
This host shift from hawthorns to apples may be
the first step toward sympatric speciation —in
fewer than 200 years, some genetic differences
between these two groups of flies have evolved
+
Hawthorns
Apples
Evidence for Speciation?
Speciation is a long process, but we can find evidence for
it in PATTERNS OF EVOLUTION
PATTERNS OF EVOLUTION
Adaptive radiation
Convergent Evolution
Coevolution
Rate of Speciation
Coevolution
• Many species evolve in close relationship with
other species.
Coevolution
• The relationship might be so close that the evolution
of one species affects the evolution of other
species. This is called coevolution.
• For Example: Mutualism - when two species benefit
each other.
Coevolution – EXAMPLE 1
• comet orchids and the moths that pollinate them have
coevolved an intimate dependency
• the foot long flowers of this plant perfectly match the footlong tongue of the moth
Coevolution – EXAMPLE 2
• One species can evolve a parasitic dependency on another
species.
• This type of relationship is often called a coevolutionary
arms race
Coevolution – EXAMPLE 2
• A plant and an insect that is dependent on the plant for
food.
– The plant population evolves a chemical defense against the insect
population.
– The insects, in turn, evolve the biochemistry to resist the defense.
– The plant then steps up the race by evolving new defences, the insect
escalates its response, and the race goes on.
PATTERNS OF EVOLUTION
Adaptive radiation
Convergent Evolution
Coevolution
Rate of Speciation
Adaptive Radiation = divergent evolution
• can occur in a relatively short time when one species gives
rise to many species in response to the creation of new
habitat or another ecological opportunity.
Adaptive Radiation = divergent evolution
• Adaptive radiation often follows large - scale extinctions (such
as the extinction of dinosaurs and subsequent rise of mammals)
• These different species have homologous structures
Adaptive Radiation – EXAMPLE 1
• More than 300 species of cichlid fish once lived in Africa’s Lake
Victoria.
• Data shows that these species diverged from a single ancestor
within the last 14,000 years.
PATTERNS OF EVOLUTION
Adaptive radiation
Convergent Evolution
Coevolution
Rate of Speciation
Adaptive Radiation = divergent evolution
Produces Homologous
Structures
Convergent Evolution
common adaptations to similar
environments
Convergent Evolution
occurs when
organisms that are
NOT closely
related (they have
no common
ancestors) live in
the SAME
environment in
different parts of
the world.
Convergent Evolution – Example 1
• all of these animals live or lived in an ocean but
they are not closely related
Convergent Evolution
These species independently evolved similar traits or structures
which are adapted to that same environment
What similar traits or structures these three animals
gained during the course of evolution?
Convergent Evolution
Flippers, streamlined body, ability to swim
What similar traits or structures these three animals
gained during the course of evolution?
Convergent Evolution
Prickles, thorns and spines
Convergent Evolution
They have evolved independently to
prevent or reduce herbivory
(eating of plants by organisms)
Convergent Evolution
Produces Analogous
Structures
Adaptive Radiation = divergent evolution
Produces Homologous
Structures
Analogues Structures
VS.
Homologues Structures
Analogues
Structures
VS.
Different internal structures
Same Function
Similar Environments
Result of Convergent
Evolution
Homologues
Structures
Same internal structures
Different Functions
Different Environments
Result of Divergent
Evolution
PATTERNS OF EVOLUTION
Adaptive radiation
Convergent Evolution
Coevolution
Rate of Speciation
Rate of Speciation
• Evolution is a dynamic process: traits might change rapidly OR
traits might remain unchanged for millions of years.
• Some scientists think that evolution proceeds in small, gradual
steps = gradualism. A great deal of evidence favors this
theory.
# of
species
Time
Rate of Speciation
• However, the fossil record contains instances of abrupt
transitions.
• Certain species of fossil snails looked the same for millions of
years, then the shell shape changed dramatically in only a few
thousand years = punctuated equilibrium
Rate of Speciation
• However, the fossil record contains instances of abrupt
transitions.
• Certain species of fossil snails looked the same for millions of
years, then the shell shape changed dramatically in only a few
thousand years = punctuated equilibrium
# of
species
Time