What Homologies tell us

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What Homologies tell us

• Similarities in structure and chemistry provide
  powerful evidence that all living things evolved
  from a common ancestor
• Darwin Concluded
• Living organisms evolved through gradual
  modifications of earlier forms ? descent with
  modification

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What Similarities tell us

• Two types of evolution can account for homologous
  AND analogous structures
• Convergent evolution
• Divergent evolution

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What Similarities tell us

• Divergent evolution two species evolve from a
  common ancestor (speciation)
• They share similarities in anatomy, biochemistry,
  and embryology due to common ancestry
• Explains homologous structures

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What Similarities tell us

• Convergent two species apparently becoming more
  similar
• Two species have adapted in similar ways to
  similar environmental conditions
• NOT due to common ancestry
• Explains analogous structures

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Convergent Evolution

• Ocotillo from California and allauidi from
  Madagascar have evolved similar mechanisms for
  protecting themselves

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Convergent Evolution

• Adaptive radiation of anoles has occurred on the
  islands of the Greater Antilles in a convergent
  fashion. On each island, different species of
  the lizards have adapted to living in different
  parts of trees, in strikingly similar ways.

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Convergent Evolution
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Convergent Evolution
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Diversity of Life

• Fitness
• Physical traits and behaviors that enable
  organisms to survive and reproduce in their
  environment arises from adaptation.
• Adaptation allows species to be better suited to
  their environment and therefore can survive and
  reproduce.

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Evolution on Different Scales

• Microevolution generation-to-generation change
  in a populations allele frequencies
• Macroevolution origin of new taxonomic groups
  speciation

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4 Driving Forces behind Evol.

• Mutation
• Any change in the original DNA
• ONLY ultimate source of variation in a population
• Gene Flow
• Movement of genes either into or out of a
  population
• Migration Immigration (add alleles) and
  Emigration (subtract alleles)

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4 Driving Forces behind Evol.

• Genetic Drift
• Change in the allele frequency in a small
  population by chance alone
• Bottleneck Effect
• Founder Effect

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4 Driving Forces behind Evol.

• Genetic Drift
• Bottleneck Effect population undergoes a high
  mortality rate genetic variation decreases
  dramatically
• Ex Cheetahs

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Genetic Drift Bottleneck Effect
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4 Driving Forces behind Evol.

• Genetic Drift
• Founder Effect few individuals leave a large
  population to start their own gene pool is very
  limited
• Ex polydactyly in PA Amish

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Genetic Drift Founder Effect
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Genetic Drift Founder Effect
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4 Driving Forces behind Evol.

• Selection
• Natural differential success in the
  reproduction of different phenotypes resulting
  from the interaction of organisms with their
  environment
• Nature does the selecting

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4 Driving Forces behind Evol.

• Selection (Natural)
• Resistance overuse of insecticides and
  antibiotics have bred resistant species of bugs
  and germs

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4 Driving Forces behind Evol.

• Selection
• Artificial breeding of domesticated plants and
  animals
• Humans intentionally do the selecting
• Cabbage, cauliflower, Brussels sprouts,
  kale, kohlrabi and broccoli have a
  common ancestor in one species of wild
  mustard

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4 Driving Forces behind Evol.

• Problems with artificial selection not enough
  genetic variation

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4 Driving Forces behind Evol.

• Selection (Sexual)
• Intrasexual selection selection within the same
  sex (competition, usually between males
• Competition, usually between males
• Exaggerated anatomy

Bighorn Sheep
Rocky Mountain Elk
Five-horned Rhinoceros Beetles
Stagbeetles
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4 Driving Forces behind Evol.

• Selection (Sexual)
• Intersexual selection one sex selects mate
  based on phenotypes
• Exaggerated anatomy

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• Selection can influence populations in three
  major ways
• Directional Sel.
• Stabilizing Sel.
• Disruptive (diversifying) Sel.

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Directional Selection

• Environment selects against one phenotypic
  extreme, allowing the other to become more
  prevalent

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Disruptive Selection

• Environment selects against intermediate
  phenotype, allowing both extremes to become more
  prevalent

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Stabilizing Selection

• Environment selects against two extreme
  phenotypes, allowing the intermediates to become
  more prevalent

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Key Points

1. Natural selection does not cause genetic changes
   in individuals.
2. Natural selection acts on individuals evolution
   occurs in populations.
3. Evolution is a change in the allele frequencies
   of a population, owing to unequal success at
   reproduction among organisms bearing different
   alleles.
4. Evolutionary changes are not good nor
   progressive in any absolute sense.

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Evolutionary Theory

• Foundation on which the rest of the biological
  science is built. Collection of carefully
  reasoned and tested hypotheses about how
  evolutionary change occurs.

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Speciation

• What is a species?
• Biological definition a group of closely related
  organisms (population) that can interbreed to
  produce fertile, viable offspring

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Speciation

• Why cant/dont populations interbreed?
• Prezygotic barriers
• Postzygotic barriers

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Prezygotic Barriers

• Ecological (habitat) isolation pops live in
  different habitats and do not meet
• Parasites generally dont transfer hosts
• Temporal isolation active or fertile at
  different times
• Flowering plants pollinate on different days or
  different times of the day

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Prezygotic Barriers

• Behavioral isolation differences in activities
• Mating calls or actions are different

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Prezygotic Barriers

• Mechanical isolation mating organs do not fit
  or match
• Enough said
• Gametic isolation gametes cannot combine
• Sperm destroyed in different vaginal cavity
• Sperm and egg dont fuse due to different
  membrane proteins

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Postzygotic Barriers

• Hybrid inviability hybrid zygotes fail to
  develop or reach sexual maturity
• Hybrid infertility hybrids fail to produce
  functional gametes

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Summary

• 2 or more mechanisms may occur at once
• Ex Bufo americanus and Bufo fowleri are
  ecologically, temporally, and behaviorally
  isolated
• Bufo americanus breeds in early spring in small,
  shallow puddles or nearby dry creeks
• Bufo fowleri breeds in late spring in large pools
  and streams
• Their mating calls also differ

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Limitations of Biological Species Concept

• How do you classify organisms that
• have the potential to interbreed, but do not do
  so in nature?
• do not reproduce sexually?
• exist only as fossils?
• Alternative species concepts (ecological,
  pluralistic, morphological, genealogical) help
  address limitations

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Modes of Speciation

• Allopatric (Greek, allos other Latin, patria
  homeland)
• Speciation due to geographic separation
• Barrier stops gene flow between populations
• Evolutionary change acts independently on each
  pop to establish reproductive barriers

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• Mitochondrial DNA analysis has shown that certain
  tamarin monkey pops (those separated by wide
  rivers) are diverging toward speciation

• Where the Amazon is very wide, tamarins on one
  side are brown, but on the other side are white.
  Where the Amazon is narrow, tamarins of both
  colors are found on either side

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Allopatric Speciation

• Birds can move freely across the gorge of the
  Grand Canyon squirrels cannot
• Two species arose when their original pop was
  disrupted by the carving of the canyon

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• A. harrisi
• A. leucurus

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Allopatric Speciation

• If not given enough time, speciation will not
  occur
• Also, even if they do
  come back together, they
  need to interbreed to be the same
  species

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Allopatric Speciation

• Figure 24.11
• Adaptive Radiation evolution of
  many diversely-adapted species from a
  common ancestor
• Ex Hawaiian archipelago

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Sympatric Speciation

• Sympatric (Greek, sym together Latin, patria
  homeland)
• Speciation occurs in populations that share a
  habitat
• Results from
• Ecological isolation
• Polyploidy (number of sets of chromosomes
  increases)

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Sympatric Speciation

• Polyploidy (number of sets of chromosomes
  increases)
• A result of accidents in meiosis

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Will Speciation Occur?

• p q 1
• p2 2pq q2 1
• Will speciation occur? You tell me!
• Hardy-Weinberg PPT 1
• Hardy-Weinberg PPT 2

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Evolutionary Time Scales

• Evolution can take a long time or can occur
  relatively quickly
• Gradualism
• Punctuated Equilibrium

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Evolutionary Time Scales

• Gradualism big evolutionary changes are the
  result of many small ones over a long period of
  time

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Evolutionary Time Scales

• Punctuated Equilibrium speciation occurs fairly
  rapidly then remain constant

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Evolutionary Novelties

• Unique and highly specialized organs seem to
  complicated to have been naturally selected
• Ex eyes are really just photoreceptors some are
  more developed, but all do the basic function
  receive light

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Evolutionary Novelties
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Evo-devo

• Evolutionary development
• A field of interdisciplinary research that
  examines how slight genetic divergences can
  become magnified into major morphological
  differences between species

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Evo-devo

• By blocking expression of one gene, researchers
  forced a chickens foot to develop to resemble a
  ducks foot
• Two embryos from the same animal

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Evo-devo

• Left, a normal chicken leg will develop

• Right, a normal duck leg will develop from a
  chicken embryo
• Chicken leg scaled with 4 digits
• Duck leg smooth and webbed
• Duck legs, due to one genetic evolutionary
  difference, help ducks do many things chickens
  cannot, like swim