Speciation
Speciation
v
What is a species?
v
The Process of Speciation
v
Models of Speciation
v
Interesting examples of Speciation
Chapter 2.7, Bush
Speciation
v
What is a species?
What is a species?
v
The Process of Speciation
v
Models of Speciation
v
Interesting examples of Speciation
Morphological Species Concept
v
Morphological Species Concept
v
Biological Species Concept
v
Modern Species Concepts
Defining species is complicated
v
Linnaeus invented the
system of classifying
organisms in the
1800’s
v
Phenotypic variation within species may
make us think that there is more than
one species
v
He based the
classification of a
species by appearance
v
Different species may look remarkably
similar
Different phenotypes within a single species
Different species with similar appearance
Western Meadowlark
Eastern and Western Meadowlarks
look identical but differ in their song
Hydrangea
Eastern Meadowlark
Different species with similar appearance
Some species look
similar even when
they are only very
distantly related =
CONVERGENT
EVOLUTION
Cacti (Americas)
“Species are groups of potentially or
actually interbreeding natural
populations that are reproductively
isolated from other such groups”
-Mayr, 1942
Euphorbia (Africa)
Defining species is still complicated
v
Biological Species Concept
Modern species concepts
Must revert to Linnaeus’ system for:
– extinct organisms
– asexual organisms
– some distinct species that can still
interbreed and produce viable offspring
(e.g., coyotes, wolves, and dogs)
If >5% of amino acids are different, then consider two
organisms to be of different species
Speciation
v
What is a species?
v
The Process of Speciation
v
Models of Speciation
v
The Process of Speciation
v
Speciation ≠ Evolution
– populations can evolve too
e.g. Ground finch size during drought
v
SPECIATION:
– is the process in which a new species is
formed from an initial one
Interesting examples of Speciation
The Process of Speciation
One species (set
of interbreeding
organisms)
Genetic variant spreads through
part of the species; bearers of this
variant must mate only with other
bearers of the same variant
How Speciation occurs:
Two species. Further
phenotypic, behavioural
and ecological
differences may evolve
Evidence for both types of speciation
v
It is thought that most speciation has
been allopatric
v
Sympatric speciation is thought to occur
often among flowering plants (2-4% of
species formed through this process)
Allopatric speciation
The Grand Canyon prevents dispersal of squirrels to
opposite side, allowing divergence
Chance events influence evolution
Sympatric speciation via polyploidization
Barriers to interbreeding
Founder effects
Chromosome evolution in animals
Speciation
Two species have been formed if breeding is
prevented:
v
What is a species?
1) Prezygotic barrier – E.g. don’t live in the
same habitat (e.g., squirrels in the Grand
Canyon)
v
The Process of Speciation
v
Models of Speciation
v
Interesting examples of Speciation
2) Postzygotic barrier – E.g. offspring are
inviable or sterile (e.g., in polyploid vs. diploid
species)
Models of Speciation
v
Gradualism vs. Punctuated Equilibrium
Gradualist Model:
– Darwin thought species arose gradually
and slowly
v
Punctuated Equilibrium Model:
– speciation occurs in quick bursts followed
by long periods of no change
– Fossil record supports this model but is
incomplete
Speciation
v
Adaptive radiation of Darwin’s finches
What is a species?
v
The Process of Speciation
v
Models of Speciation
v
Interesting examples of Speciation
Ring Species – One species or two?
Ensantina salamanders
single ancestral
species arrived
from mainland S.
America millions of
years ago, radiated
into 13 species
with specialized
feeding habits
Co-speciation of host and parasite
Changing Environments and Evolution
Ch. 2, 22.4-22.6, Bush
Changing environments and Evolution
Changing environments and Evolution
v
Early Earth and the Origin of Life
v
Early Earth and the Origin of Life
v
Major events in the history of life
v
Major events in the history of life
v
Continental drift and life as we know it
v
Continental drift and life as we know it
v
Present day environmental changes
v
Present day environmental changes
Early Earth
v
Earth was formed ~4,500,000,000 yrs ago
vEarth was very hot and constantly bombarded
from space
vAt this point there was no liquid water, life was
impossible
v
About 3,900,000,000 yrs ago, Earth was
solidified enough and cool enough for liquid
water
vLife apparently arose shortly thereafter
Formation of ingredients for life
v
1950’s – Muller and
Urey found that the
input of electrical
energy could spur
the creation of
organic compounds
from inorganic
compounds and
ocean water
The transition from molecules to life
v
the step from amino acids to replicating life is
still a mystery
v
biochemical clues suggest that there may
have been life on the planet as early as 3.8
billion years ago
v
v
As our understanding of our own solar system has
increased, the hypothesis that life is not restricted to
Earth has received more attention.
– Europa (a moon of Jupiter):
v may have liquid water beneath the surface and may
support life
– Mars:
v is cold, dry, and lifeless today, but was probably
relatively warmer, wetter, and had a CO2-rich
atmosphere billions of years ago
vMars’ subsurface may still be capable of having life
vMany scientists see Mars as an ideal place to test
hypotheses about Earth’s prebiotic chemistry
Deep Sea vents
Essentially no
atmospheric O2
– Highly corrosive,
destroys molecules
v
Highly energetic
– Lightning, volcanic
activity, UV radiation
high
– Provide energy for
chemical reactions
First fossils are 3.5 billion years old
(resemble modern day bacteria)
Could life originate elsewhere?
v
Environment for early life forms
Where did first life forms evolve?
v
Previously assumed to be on the
surface of the ocean
v
Now, it is thought that life evolved in
hydrothermal vents in the deep ocean
where no photosynthesis takes place
– sulphide-rich water and heat provided the
necessary elements for life’s reactions
Changing environments and Evolution
v
Early Earth and the Origin of Life
v
Major events in the history of life
v
Continental drift and life as we know it
v
Present day environmental changes
A clock analogy for Life’s History
v
Major events are:
The Evolution of Photosynthesis
v
Photosynthesis: Using sunlight to create
carbohydrate from CO2
v
First photosynthetic organisms used
Hydrogen sulphide and created sulphur as a
by-product
v
Modern day photosynthesis uses only CO2
and water and produces O2 as by-product
– Photosynthesis
– Multicellularity
– Invasion of land
– Humans (come into
the picture a few
minutes to 12:00)
Oxygen changed the world
v
Over the next 3 billion years, the oceans
became saturated with O2
v
organisms that could not tolerate O2 went
extinct (or became very rare and restricted to
O2-free environments)
v
Ozone layer allows life on land
v
By 400 million years ago, O2 levels
were approximated modern levels
v
Ozone layer blocks the UV radiation,
which causes mutations, allowing
organisms to invade land
800 million years ago, O2 starts seeping into
atmosphere creating the ozone layer
Early changes in the environment
Cambrian Explosion of multicellular organisms
v
Earliest known fossils of multicellular
organisms, 600 mya
v
540-505 mya huge diversity of organisms
present in the fossil record
v
Best fossils displaying Cambrian explosion
are in the Burgess Shales in the Canadian
Rockies
Determining the Earth’s History
Fossils of Early life forms
v
v
microscopic
found in 3.4 billion
year-old rock
Cambrian fossils
Other well-preserved fossils
Other well-preserved fossils
Other well-preserved fossils
Changing environments and Evolution
v
Early Earth and the Origin of Life
v
Major events in the history of life
v
Continental drift and life as we know it
v
Present day environmental changes
Pangaea
v
Until 200 mya, all continents were
clustered together at tropical latitudes
v
As plates of Pangaea broke off, each
plate carried a different set of life forms
Australia and Antarctica
v
Have been isolated from the other
continents for the longest time
v
Resulted in them having the most
unique flora and fauna
ve.g., marsupials
Continental Drift
v
continents ride across the surface of
Earth, propelled by powerful volcanic
forces
v
explains some basic patterns of
similarity and dissimilarity of flora and
fauna
The Drifting of Continents
Unique flora and fauna of Australia
Changing environments and Evolution
v
Early Earth and the Origin of Life
v
Major events in the history of life
v
Continental drift and life as we know it
v
Recent Ozone changes
• Human activities
have:
• increased ozone in
the troposphere
• decreased ozone
in the stratosphere
“Good” ozone
(protects Earth from
UV radiation)
Present day environmental changes
“Bad” ozone
(reactive gas)
Increases in tropospheric ozone
v
v
By-products of
burning fossil fuels
(e.g., oil. gas) react
with oxygen to make
O3
O3 reacts with
chlorophyll in plants,
detrimental to
growth
Summary
v
Life began on Earth ~ 3.5 bya
v
The evolution of photosynthetic organisms resulted in
the formation of the ozone layer, paving the way for
life on land
v
Continental drift has played a large part in shaping the
modern day distribution of organisms
v
Changes in the environment are happening today at a
rapid pace
Decreases in stratospheric ozone
v
v
CFC’s, HCFC’s and other chemicals react with O3 to make O2
decrease in O3 increases UV radiation ⇒ higher rates of cancer
(in humans and other mammals), reproductive failure in birds
and lizards, damage to plants, etc.