Speciation

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Speciation
Chapter 2.7, Bush
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Speciation

• What is a species?
• The Process of Speciation
• Models of Speciation
• Interesting examples of Speciation

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Speciation

• What is a species?
• The Process of Speciation
• Models of Speciation
• Interesting examples of Speciation

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What is a species?

• Morphological Species Concept
• Biological Species Concept
• Modern Species Concepts

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Morphological Species Concept

• Linnaeus invented the system of classifying
  organisms in the 1800s
• He based the classification of a species by
  appearance

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Defining species is complicated

• Phenotypic variation within species may make us
  think that there is more than one species
• Different species may look remarkably similar

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Different phenotypes within a single species
Hydrangea
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Different species with similar appearance
Western Meadowlark
Eastern and Western Meadowlarks look identical
but differ in their song
Eastern Meadowlark
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Different species with similar appearance

• Some species look similar even when they are only
  very distantly related CONVERGENT EVOLUTION

Cacti (Americas)
Euphorbia (Africa)
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Biological Species Concept

• Species are groups of potentially or actually
  interbreeding natural populations that are
  reproductively isolated from other such groups
• -Mayr, 1942

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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)

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Modern species concepts

• If gt5 of amino acids are different, then
  consider two organisms to be of different species

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Speciation

• What is a species?
• The Process of Speciation
• Models of Speciation
• Interesting examples of Speciation

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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

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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
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How Speciation occurs
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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)

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Allopatric speciation

• The Grand Canyon prevents dispersal of squirrels
  to opposite side, allowing divergence

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Chance events influence evolution
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Founder effects
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Sympatric speciation via polyploidization
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Chromosome evolution in animals
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Barriers to interbreeding

• Two species have been formed if breeding is
  prevented
• 1) Prezygotic barrier E.g. dont 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)

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Speciation

• What is a species?
• The Process of Speciation
• Models of Speciation
• Interesting examples of Speciation

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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

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Gradualism vs. Punctuated Equilibrium
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Speciation

• What is a species?
• The Process of Speciation
• Models of Speciation
• Interesting examples of Speciation

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Adaptive radiation of Darwins finches
single ancestral species arrived from mainland S.
America millions of years ago, radiated into 13
species with specialized feeding habits
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Ring Species One species or two?
Ensantina salamanders
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Co-speciation of host and parasite
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Changing Environments and Evolution
Ch. 2, 22.4-22.6, Bush
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Changing environments and Evolution

• Early Earth and the Origin of Life
• Major events in the history of life
• Continental drift and life as we know it
• Present day environmental changes

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Changing environments and Evolution

• Early Earth and the Origin of Life
• Major events in the history of life
• Continental drift and life as we know it
• Present day environmental changes

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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

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Formation of ingredients for life

• 1950s Muller and Urey found that the input of
  electrical energy could spur the creation of
  organic compounds from inorganic compounds and
  ocean water

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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)

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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

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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 Earths prebiotic chemistry

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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 lifes reactions

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Deep Sea vents
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Changing environments and Evolution

• Early Earth and the Origin of Life
• Major events in the history of life
• Continental drift and life as we know it
• Present day environmental changes

• Early Earth and the Origin of Life
• Major events in the history of life
• Continental drift and life as we know it
• Present day environmental changes

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A clock analogy for Lifes History

• Major events are
• Photosynthesis
• Multicellularity
• Invasion of land
• Humans (come into the picture a few minutes to
  1200)

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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

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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

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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

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Early changes in the environment
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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

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Determining the Earths History
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Fossils of Early life forms

• microscopic
• found in 3.4 billion year-old rock

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Cambrian fossils
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Other well-preserved fossils
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Other well-preserved fossils
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Other well-preserved fossils
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Changing environments and Evolution

• Early Earth and the Origin of Life
• Major events in the history of life
• Continental drift and life as we know it
• Present day environmental changes

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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

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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

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The Drifting of Continents
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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

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Unique flora and fauna of Australia
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Changing environments and Evolution

• Early Earth and the Origin of Life
• Major events in the history of life
• Continental drift and life as we know it
• Present day environmental changes

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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)
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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

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Decreases in stratospheric ozone

• CFCs, HCFCs 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.

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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