Speciation

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• Topics
• Speciation and Reproductive Isolation
• Patterns of Evolution
• Rates of Evolution
• Origin of Life

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Speciation
Species population whose members can interbreed
in nature and produce viable, fertile offspring

• Evolution change in the allelic frequencies in a
  population

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Speciation

• Anagenesis
• Phyletic evolution
• One species replaces another
• Pattern of evolution that results in linear
  descent with no branching or splitting of the
  population.

• - Cladogenesis
• Branching evolution
• When a new species branches out from a parent
  species
• evolutionary change and diversification resulting
  from the branching off of new taxa from common
  ancestral lineages

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• Anagenesis

• Cladogenesis

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Speciation

• Allopatric Speciation
• Sympatric Speciation
• Adaptive Radiation

Animation
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Allopatric Speciation
speciation by geographic isolation

• Caused by geographic isolation
• Mountain ranges, canyons, rivers, lakes
• Interbreeding is prevented
• Gene frequencies diverge due to natural
  selection, mutation, or genetic drift.

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Allopatric Speciation

• Can occur even if the barrier is a little
  porous, that is, even if a few individuals can
  cross the barrier to mate with members of the
  other group.
• In order for a speciation even to be considered
  allopatric, gene flow between the soon-to-be
  species must be greatly reducedbut it doesnt
  have to be reduced completely to zero.

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Sympatric Speciation
Barriers to Reproduction (sexual)
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Sympatric Speciation

• Without geographic isolation
• Examples
• Balanced Polymorphism
• Polyploidy
• Hybridization
• Habitat isolation
• Temporal isolation
• Mechanical isolation
• Behavioral isolation
• Gametic isolation

Prezygotic barriers
Postzygotic barriers

• Prezygotic barriers
• PREVENT mating
• Postzygotic barriers
• Prevent the production of fertile offspring after
  mating has occurred

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Balanced Polymorphism
Sympatric Speciation

• Maintain stable frequencies of two or more
  phenotypic forms
• natural selection preserves variation
• heterozygote advantage (i.e. heterozygotes have
  the highest relative fitness).
• sickle cell anemia.
• Ex
• Population of insects that possess polymorphism
  for color.
• Can only survive where they are camouflaged.
• Become reproductively isolated, and their gene
  pools diverge creating new species.

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Polyploidy
Sympatric Speciation

• When a cell has more than two complete sets of
  chromosomes
• Common in plants
• Causes nondisjunction
• Plants that are polyploid cannot breed with
  others of the same species that are not polyploid
• The two groups become isolated from one another

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Hybridization
Parapatric Speciation

• When two closely related species mate and produce
  offspring along a geographic boundary.
• Called a hybrid zone
• Hybrids adapt to the area and eventually diverge
  from both parents.

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Sympatric Speciation

• Habitat isolation
• Species do not encounter one another
• Temporal Isolation
• Mating takes place at different times of the year
• Flowers open at different times of the day.
• Mechanical Isolation
• Male and female genitalia are structurally
  incompatible

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• Behavioral Isolation
• Populations are capable of interbreeding, but
  have different courtship rituals or other type of
  behavior.
• Do not recognizes another species as a mating
  partner.

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Gametic isolation

• Male gametes do not survive in the environment of
  the female gamete or when female gametes do not
  recognize male gametes

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Postzygotic isolating mechanisms

• Hybrid inviability
• Zygote fails to develop and aborts
• Hybrid sterility
• Hybrids become functional adults, but are
  sterile. (ex mule)
• Hybrid breakdown
• Offspring have reduced viability or fertility

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Adaptive Radiation
lineage rapidly diversifies

• The evolution of many diversely adapted species
  from a common ancestor
• Relatively rapid
• Usually occurs when a population colonizes an
  area of diverse geographic or ecological
  conditions.
• New niches
• Each species becomes specialized for a different
  set of conditions.

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lineage rapidly diversifies
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Patterns of Evolution

• Evolution change in the allelic frequencies in a
  population

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Patterns of Evolution

• Divergent Evolution
• Convergent Evolution
• Parallel Evolution
• Coevolution

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Divergent Evolution

• Occurs when a population becomes isolated from
  the rest of the species.
• Becomes exposed to new selective pressures
• Evolves into a new species

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Convergent Evolution

• When unrelated species occupy the same
  environment and are subjected to similar
  selective pressures.
• Show similar adaptations.

• Ex Whale and Shark
• Not related, but have similar features that are
  adapted for their environment.

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Parallel Evolution

• Two related species that have made similar
  evolutionary adaptations after their divergence
  from a common ancestor.
• Ex Marsupial mammals of Australia and placental
  mammals of North America.
• Similar environments

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Coevolution

• Predators and their prey
• Parasites and their hosts
• Plant-eating animals and the plants upon which
  they feed
• One example of coevolution is between plants and
  the animals that pollinate them.

Coevolution is the joint change of two or more
species in close interaction.
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Rates of Evolution

• Evolution change in the allelic frequencies in a
  population

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Rates of Evolution

• Punctuated Equilibrium
• Phyletic Gradualism

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Gradualism

• Organisms descend from a common ancestor slowly
  over a long period of time.

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Punctuated Equilibrium

• Favored theory
• New species appear suddenly after long periods of
  stasis.

sporadically (by splitting) and occurs relatively
quickly
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Origin of Life
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History of Life
1. Life on Earth originated between 3.5 and 4.0
billion years ago. (Anaerobic heterotrophic
prokaryotes) 2. Prokaryotes dominated
evolutionary history from 3.5 to 2.0 billion
years ago 3.Oxygen began accumulating in the
atmosphere about 2.7 billion years ago
(Photosynthesis) 4.Single celled eukaryote began
by 2.1 billion years ago. (Theory of
Endosymbiosis) 5.Multicellular eukaryotes evolved
1.2 billion years ago 6.Plants, fungi, and
animals colonized the land about 500 million
years ago.
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The first cells may have originated by chemical
evolution on a young Earth

• Most scientists favor the hypothesis that life on
  Earth developed from nonliving materials that
  became ordered into aggregates that were capable
  of self-replication and metabolism.
• From the time of the Greeks until the 19th
  century, it was common knowledge that life
  could arise from nonliving matter, an idea called
  spontaneous generation.
• While this idea had been rejected by the late
  Renaissance for macroscopic life, it persisted as
  an explanation for the rapid growth of
  microorganisms in spoiled foods.

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• In 1862, Louis Pasteur conductedbroth
  experimentsthat rejected the idea of
  spontaneousgeneration even for microbes.
• A sterile brothwould spoil onlyif
  microorganismscould invade fromthe environment.

-created the first vaccine for rabies
-pasteurization.
Swan flask
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• Early life
• Under one hypothetical scenario this occurred in
  four stages
• (1) The abiotic synthesis of small organic
  molecules
• (2) The joining these small molecules into
  polymers
• (3) The origin of self-replicating molecules
• (4) The packaging of these molecules into
  protobionts.
• This hypothesis leads to predictions that can be
  tested in the laboratory.

Protobionts aggregates of abiotically produced
molecules surrounded by a membrane or
membrane-like structure
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• AI Oparin and J.B.S. Haldane
• 1920s
• Hypothesized separately that under the conditions
  of early earth, organic molecules could form.
• A"primeval soup" of organic molecules could be
  created in an oxygen-less atmosphere through the
  action of sunlight

AI Oparin
Could not demonstrate theory.

• J.B.S. Haldane

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• Stanley Miller and Harold Urey
• 1953, Tested the Oparin-Haldane hypothesis

Stanley Miller
Harold Urey
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• Stanley Miller and Harold Urey
• 1953, Tested the Oparin-Haldane hypothesis

• Proved that almost any energy sources would have
  converted the molecules in the early atmosphere
  into organic molecules like amino acids
• Discharged sparks in an atmosphere ofgases and
  water vapor
• Produced a variety of amino acids and other
  organic molecules

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• Sidney Fox
• Carried out similar experiments to Miller and
  Urey
• He began with organic molecules and was able to
  produce membrane-bound, cell-like structures he
  called proteinoid microspheres.

-Early work demonstrated that under certain
conditions amino acids could spontaneously form
small polypeptides
-studied the spontaneous formation of protein
structures
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EXTRASAdditions

• Outbreeding
• Opposite of inbreeding
• Mating with individual that are not closely
  related
• Ex plants that have male and female parts that
  mature at different times
• Helps insure genetic diversity
• Evolutionary neutral traits
• Trait that have no selective value
• Ex blood type, fingerprints

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• Life on Earth-David Attenbourgh Pt3-Video CLip