Review

1
Review

• All populations of species have within them
  genetic variation that results in qualitative and
  quantitative differences in phenotype
• Environments cycle through periods of stasis and
  flux
• Organisms best suited to compete for available
  resources produce the most viable offspring

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What are the sources of variation?

• Mutations in genes
• Recombination of alleles during meiosis (crossing
  over)
• Orientation of homologous chromosomes during
  metaphase I
• Fertilization (one sperm and egg out of many
  variations)

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What causes the change of variation (allele
frequency) within a population?

• Mutations
• Gene flow (immigration)
• Nonrandom mating
• Genetic drift (founder and bottleneck effects)
• Selection (artificial and natural)

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The Origin of Species
Mom, Dad Theres something you need to
know Im a MAMMAL!
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That mystery of mysteries

• Darwin never actually tackled how new species
  arose

Both in space and time, we seem to be brought
somewhat near to that great factthat mystery
of mysteriesthe first appearance of new beings
on this Earth.
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Sowhat is a species?

• Biological species concept
• population whose members can interbreed produce
  viable, fertile offspring
• reproductively compatible

Distinct speciessongs behaviors are different
enough to prevent interbreeding
Western Meadowlark
Eastern Meadowlark
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How and why do new species originate?

• Species are created by a series of evolutionary
  processes
• populations become isolated
• geographically isolated
• reproductively isolated
• isolated populations evolve independently
• Isolation
• allopatric
• geographic separation
• sympatric
• still live in same area

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Speciation

• The process by which a new species is formed from
  a related preexisting species
• The development of a new branch on the tree of
  life
• The formation of a new and isolated gene pool

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• Begin class by working on speciation vocabulary
  assignment for 10 minutes
• Please do so QUIETLY

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Hardy-Weinberg Equilibrium

• Assume a population of monkeys living on an
  island is in Hardy-Weinberg equilibrium
• No mutations, large population size, no gene
  flow, no genetic drift, no natural selection.
• This means that the allele frequencies of the
  gene pool does not change from one generation to
  the next.
• 1p2 2pq q2
• If 25 of the monkeys exhibit the dominant trait
  of black fur, and there are 200 monkeys in the
  population, how many of have a heterozygous
  genotype?

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Factors the affect variation within a population
(Changes allele frequency in a gene pool)

• Mutations
• Immigration
• Independent Assortment
• Bottleneck Effect
• Natural Selection
• Random Fertilization
• Emmigration
• Non-random Mating
• Crossing Over (meiosis)

Reduces Variation Increases Variation
In your notes, fill in the t-chart above with the
terms listed to the right
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Isolation Leads to Speciation
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Types of Isolating Mechanisms

• Pre-zygotic Isolating Mechanisms
• Ecological
• Geographical
• Mechanical
• Temporal
• Behavioral
• Gametic

• Post-zygotic Isolating Mechanisms
• Reduced Hybrid Viability
• Reduced Hybrid Fertility
• Hybrid Breakdown

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PRE-reproduction barriers

• Obstacle to mating or to fertilization if mating
  occurs

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Geographic isolation

• Species occur in different areas
• physical barrier
• Ex. canyon, river, forest, desert, ocean,
  mountain, etc.
• allopatric speciation
• other country

Ammospermophilus spp
Harriss antelope squirrel inhabits the canyons
south rim (L). Just a few miles away on the north
rim (R) lives the closely related white-tailed
antelope squirrel
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Geographical Isolation
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Ecological isolation

• Species occur in same region, but utilize
  habitats differently so they rarely encounter
  each other
• Sympatric speciation (same country)

2 species of garter snake, Thamnophis, occur in
same area, but one lives in water other is
terrestrial
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Ecological Isolation

• The Anopheles genus consists of six mosquito
  species
• The species are virtually indistinguishable
  morphologically, but are isolated reproductively
• They breed in different habitats.
• Some breed in brackish water, others in running
  fresh water, and still others in stagnant fresh
  water.

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Temporal isolation

• Species that breed during different times of day,
  different seasons, or different years cannot mix
  gametes
• reproductive isolation
• sympatric speciation

Eastern spotted skunk (L) western spotted skunk
(R) overlap in range but eastern mates in late
winter western mates in late summer
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Temporal Isolation
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Behavioral isolation

• Unique behavioral patterns rituals isolate
  species
• identifies members of species
• attract mates of same species
• courtship rituals, mating calls, etc.

Blue footed boobies mate only after a courtship
display unique to their species
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Recognizing your own species
courtship songs of sympatricspecies of lacewings
courtship display of Gray-Crowned Cranes, Kenya
firefly courtship displays
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Mechanical isolation

• Morphological differences can prevent successful
  mating

Plants
Even in closely related species of plants, the
flowers often have distinct appearances that
attract different pollinators. These 2 species
of monkey flower differ greatly in shape color,
therefore cross-pollination does not happen.
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Mechanical isolation
Animals

• For many insects, male female sex organs of
  closely related species do not fit together,
  preventing sperm transfer
• lack of fit between sexual organs hard to
  imagine for us but a big issue for insects with
  different shaped genitals!

Damsel fly penises
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Mechanical isolation

• Bush babies, a group of small arboreal primates,
  are divided into several species based on
  mechanical isolation.
• Each species has distinctly shaped genitalia
  that, like locks and keys, only fit with the
  genitalia of its own species.

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Gametic isolation

• Sperm of one species may not be able to fertilize
  eggs of another species
• mechanisms
• biochemical barrier so sperm cannot penetrate egg
• receptor recognition lock key between egg
  sperm
• chemical incompatibility
• sperm cannot survive in female reproductive tract

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POST-reproduction barriers

• Prevent hybrid offspring from developing into a
  viable, fertile adult
• reduced hybrid viability
• reduced hybrid fertility
• hybrid breakdown

zebroid
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Reduced hybrid viability

• Genes of different parent species may interact
  impair the hybrids development

Species of salamander genus, Ensatina, may
interbreed, but most hybrids do not complete
development those that do are frail.
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Reduced hybrid fertility

• Even if hybrids are vigorous they may be sterile
• chromosomes of parents may differ in number or
  structure meiosis in hybrids may fail to
  produce normal gametes

Mules are vigorous, but sterile
Donkeys have 62 chromosomes (31 pairs)
Horses have 64 chromosomes (32 pairs)
Mules have 63 chromosomes!
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Reduced Hybrid Fertility
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The Liger -massive, but sterile
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Hybrid breakdown

• Hybrids may be fertile viable in first
  generation, but when they mate offspring are
  feeble or sterile

In some strains of cultivated rice, hybrids are
vigorous but plants in next generation are small
sterile. On path to separate species.
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Isolation Can Lead to Speciation
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One Gene Pool
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Isolation
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Independent Adaptation
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Many Generations
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Removal of Barrier
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Design an Experiment!

• Work with a partner, record your ideas on a
  separate sheet of paper that will be turned in.
• Choose a laboratory organism
• Fruit fly, convict cichlid, pea plant
• Develop an experiment that you think could result
  in the formation of two distinct species from the
  original.
• Describe your procedure in as much detail as you
  can, as if you were going to perform this
  experiment.
• Hint How will you know when two species have
  formed?

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Trends in Evolution

• Adaptive Radiation
• Divergent Evolution
• Convergent Evolution
• Gradualism
• Punctuated Equilibrium
• Polyploidy
• Transient Polymorphism
• Balanced Polymorphism

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Divergent Evolution

• Speciation often happens repeatedly, to form a
  group of species from one ancestral lineage.
• Often these species evolve in different ways due
  to random genetic variation and varying selective
  pressures
• This is known as divergence

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Adaptive Radiation

• Rapid and repeated divergence
• Often occurs when a multiple varying niches are
  available

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Convergent Evolution

• Organisms sometimes adapt similar solutions to
  physiological problems presented by similar
  selective pressures
• Unrelated species show striking similarities

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• Convergent Evolution of Marsupial and Placental
  Mammals

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Rate of Speciation

• Current debate
• Does speciation happen gradually or rapidly
• Gradualism
• Charles Darwin
• Charles Lyell
• Punctuated equilibrium
• Stephen Jay Gould
• Niles Eldredge

Niles Eldredge Curator American Museum of Natural
History
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Gradualism

• Gradual divergence over long spans of time
• assume that big changes occur as the accumulation
  of many small ones

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Punctuated Equilibrium

• Rate of speciation is not constant
• rapid bursts of change
• long periods of little or no change
• species undergo rapid change when they 1st bud
  from parent population

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Visualizing Evolution
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The Cambrian Explosion Evidence of Punctuated
Equilibrium
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The Tale of Two Snails
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Environment Changes
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Snails in new environment adapt
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Two different population
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Environment keeps changing
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Survival of the Fittest
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Everythings back to normal (kind of)
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The Fossil Record
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Polyploidy

• Errors during meiotic cell division result in
  extra sets of chromosomes, a condition called
  polyploidy
• 30-70 of flowering plants thought to be
  polyploid
• Polyploid types are labeled according to the
  number of chromosome sets in the nucleus
• triploid (three sets 3x), for example the
  phylum Tardigrada
• tetraploid (four sets 4x), for example
  Salmonidae fish
• Pentaploid (five sets 5x)
• hexaploid (six sets 6x), for example wheat,
  kiwifruit
• octaploid (eight sets 8x), for example
  Acipenser (genus of sturgeon fish)
• decaploid (ten sets 10x), for example certain
  strawberries
• dodecaploid (twelve sets 12x), for example the
  plant Celosia argentea and the amphibian
  Xenopus ruwenzoriensis

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Speciation via polyploidy

• A diploid cell undergoes failed meiosis,
  producing diploid gametes, which self-fertilize
  to produce a tetraploid zygote.

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Polymorphisms Traits with multiple, distinct
phenotypes (morphs)
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Transient Polymorphisms

• One morph or allele with gradually replace the
  other as generations pass because it confers a
  reproductive advantage
• Pepper Moth is the classic example of this.

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Pepper Moths
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Balanced Polymorphism

• The various morphs are maintained with a
  population throughout multiple generations
• Sickle Cell Anemia is the most thoroughly
  researched example of this.

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Evolution is not goal-oriented

• An evolutionary trend does not mean that
  evolution is goal-oriented.
• Surviving species do not represent the peak of
  perfection.
• There is compromise random chance involved as
  well
• Is this also true for humans as well?