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Lecture 4: Phylogeny and the Tree of Life Campbell & Reece: Chapter 26

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Lecture 4: Phylogeny and the Tree of Life Campbell & Reece: Chapter 26 E.g., schistosomiasis Schistosomiasis: knowledge of species diversity and evolutionary history ... – PowerPoint PPT presentation

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Title: Lecture 4: Phylogeny and the Tree of Life Campbell & Reece: Chapter 26


1
Lecture 4 Phylogeny and the Tree of Life
Campbell Reece Chapter 26
2
All life is interconnected by descent
How to determine the pattern of descent?
3
Systematics - field of biology dealing with
diversity and evolutionary history of life
  • Includes Taxonomy DINC
  • Description
  • Identification
  • Nomenclature
  • Classification
  • Goal
  • Determine Evolutionary History (Phylogeny) of Life

4
Description
  • assign features
  • Character a feature (e.g., petal color)
  • Character states two or more forms of a
    character (e.g., red, white).

5
Identification
  • associate an unknown with a known
  • How? One way
  • Taxonomic Key, e.g.,
  • Tree . Species A
  • Leaves simple . Species B
  • Leaves pinnate ....... Species C
  • Herb
  • Flowers red . Species D
  • Flowers white ... Species E

6
Nomenclature
  • Naming, according to a formal system.
  • Binomial Species are two names (Linnaeus)
  • E.g., Homo sapiens
  • Homo genus name
  • sapiens specific epithet
  • Homo sapiens species name

7
Nomenclature
  • Hierarchical Ranks
  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

8
Classification
  • Placing objects, e.g., life, into some type of
    order.
  • Taxon a taxonomic group (plural taxa).

9
How to classify life
  • Phenetic classification
  • Based on overall similarity
  • Those organisms most similar are classified more
    closely together.

10
Problem with phenetic classification
  • Can be arbitrary, e.g., classify these

11
Phylogenetic classification
  • Based on known (inferred) evolutionary history.
  • Advantage
  • Classification reflects pattern of evolution
  • Classification not ambiguous

12
representation of the history of life
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Ingroup group studied Outgroup group not
part of ingroup, used to root tree
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Fig. 26-5
Branch point (node)
Taxon A
Taxon B
Sister taxa
Taxon C
ANCESTRAL LINEAGE
Taxon D
Taxon E
Taxon F
Common ancestor of taxa AF
Polytomy
17
Apomorphy (derived trait)
  • a new, derived feature E.g., for this
    evolutionary transformation scales
    --------gt feathers (ancestral feature)
    (derived feature)
  • Presence of feathers is an apomorphy for birds.

18
Taxa are grouped by apomorphies
  • Apomorphies are the result of evolution.
  • Taxa sharing apomorphies underwent same
    evolutionary history should be grouped together.

19
Principle of Parsimony
  • That cladogram (tree) having the fewest number of
    steps (evolutionary changes) is the one
    accepted.
  • Okhams razor the simplest explanation, with
    fewest number of ad hoc hypotheses, is accepted.

20
Other methods of phylogeny reconstruction
  • Maximum Likelihood or Bayesian analysis
  • Uses probabilities
  • Advantage can use evolutionary models.

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Fig. 26-11
Sequentially group taxa by shared derived
character states (apomorphies)
TAXA
Lancelet (outgroup)
Lancelet (outgroup)
Salamander
Lamprey
Lamprey
Leopard
Turtle
Tuna
Tuna
Vertebral column (backbone)
0
1
1
1
1
1
Vertebral column
Hinged jaws
0
0
1
1
1
1
Salamander
Hinged jaws
CHARACTERS
1
0
0
0
1
1
Four walking legs
Turtle
Four walking legs
0
0
0
0
1
1
Amniotic (shelled) egg
Amniotic egg
Leopard
Hair
0
0
0
0
0
1
Hair
(a) Character table
(b) Phylogenetic tree
23
Fig. 26-8a
DNA sequence data most important type of data
1
Deletion
2
Insertion
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Fig. 26-8b
DNA sequence data - alignment
3
4
Each nucleotide position Character Character
states specific nucleotide
25
Homology
  • Similarity resulting from common ancestry.
  • E.g., the forelimb bones of a bird, bat, and cat.

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Homoplasy (analogy)
  • Similarity not due to common ancestry
  • Reversal loss of new (apomorphic) feature,
    resembles ancestral (old) feature.
  • Convergence (parallelism) gain of new, similar
    features independently.

28
Convergent evolution spines of cacti euphorbs
  • Cactus

Euphorb
29
Convergent evolution spines of cacti euphorbs
30
Both examples of reversal within Tetrapods loss
of a derived feature forelimbs.
Leg-less lizards
Snake
leg-less lizards
legged lizards
snakes


Example of convergence relative to one
another! Independently evolved.
loss of legs
gain of legs (Tetrapods)
31
Convergent evolution wings of some animals
evolved independently
32
Fig. 26-7
Convergent evolution Australian mole and N.
Am. mole
33
Fig. 26-18
Ancestral gene
Gene Duplication can occur!
Ancestral species
Speciation with divergence of gene
Orthology genes homologous
Orthologous genes
Species A
Species B
(a) Orthologous genes
Species A
Gene duplication and divergence
Paralogy genes not homologous
Paralogous genes
Species A after many generations
(b) Paralogous genes
34
Common ancestry
35
Monophyletic Group
  • a group consisting of
  • a common ancestor
  • all descendents of that common ancestor

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C B F E D A
Cladograms can be flipped at nodes, show same
relationships
43
Fig. 26-13
One can date divergence times with molecular
clock and fossils
Drosophila
Lancelet
Zebrafish
Frog
Chicken
Human
Mouse
CENOZOIC
MESOZOIC
PALEOZOIC
Present
65.5
251
542
Millions of years ago
44
Relationship
  • recency of common ancestry i.e., taxa sharing
    a common ancestor more recent in time are more
    closely related than those sharing common
    ancestors more distant in time.

45
Example
  • Are fish more closely related to sharks or to
    humans?

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Example
  • Are crocodyles more closely related to lizards or
    to birds?

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Paraphyletic group
  • Consist of common ancestor but not all
    descendents
  • Paraphyletic groups are unnatural, distort
    evolutionary history, and should not be
    recognized.

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Reptilia here paraphyletic
55
Re-defined Reptilia monophyletic
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Importance of a name Did humans evolve from apes?
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Pongidae Great Apes
Hominidae
60
Pongidae Great Apes
Pongidae or Hominidae
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Pongidae or Hominidae
62
Pongidae or Hominidae
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We are human, but we are also apes.
  • We share unique human features.
  • We also share features with other apes (and with
    other animals, plants, fungi, bacteria, etc.).
  • Humans didnt evolve from apes, humans are apes.

65
Importance of systematics evolution
  • 1) Foundation of biology - study of biodiversity
  • 2) Basis for classification of life
  • 3) Gives insight into biological
    processes speciation processes adaptation to
    environment
  • 4) Can be aesthetically/intellectually pleasing!

66
E.g., schistosomiasis
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Schistosomiasis knowledge of species diversity
and evolutionary history of primary host can aid
in controlling parasite (Schistosoma, a fluke)
Phylogeny of Oncomelania snails
69
All of life is interconnected by descent.
70
There are no higher or lower species.
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