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