4 phylogeny-ch26
TRANSCRIPT
HumansRattlesnakePine treeAmoebaBacterium
All life is interconnected by descent
How to determine the pattern of descent?
Systematics - field of biology dealing with diversity and evolutionary history of life
Includes Taxonomy: DINCDescription Identification NomenclatureClassification
Goal:– Determine Evolutionary History (Phylogeny) of Life
Description
= assign features
Character = a feature (e.g., “petal color”)
Character states = two or more forms of a character (e.g., “red,” “white”).
Identification
= associate an unknown with a knownHow? One way: Taxonomic Key, e.g.,
Tree Leaves simple …….………………………… Species A Leaves pinnate …….………..…..…..…… Species B
Herb Flowers red …….…………………………… Species C Flowers white …….…………………..…… Species D
Nomenclature
Naming, according to a formal system.
Binomial: Species are two names (Linnaeus):
E.g., Homo sapiensHomo = genus namesapiens = specific epithetHomo sapiens = species name
Classification
• Placing objects, e.g., life, into some type of order.
• Taxon = a taxonomic group (plural = taxa).
How to classify life
• Phenetic classification
– Based on overall similarity
– Those organisms most similar are classified more “closely” together.
Phylogenetic classification
• Based on known (inferred) evolutionary history.
• Advantage:– Classification reflects pattern of evolution– Classification not ambiguous
Fig. 26-5
Sistertaxa
ANCESTRALLINEAGE
Taxon A
PolytomyCommon ancestor oftaxa A–F
Branch point(node)
Taxon B
Taxon C
Taxon D
Taxon E
Taxon F
Apomorphy (derived trait)
= a new, derived feature= a new, derived featureE.g., for this evolutionary transformationE.g., for this evolutionary transformation
scales --------> feathers scales --------> feathers(ancestral feature)(ancestral feature) (derived feature) (derived feature)
Presence of feathers is an Presence of feathers is an apomorphyapomorphy for birds.for birds.
Taxa are grouped by apomorphies
Apomorphies are the result of evolution.
Taxa sharing apomorphies underwent same evolutionary history should be grouped together.
Principle of ParsimonyThat cladogram (tree) having the fewest number
of “steps” (evolutionary changes) is the one accepted.
Okham’s razor: the simplest explanation, with fewest number of “ad hoc” hypotheses, is accepted.
Other methods of phylogeny reconstruction:
• Maximum Likelihood or Bayesian analysis– Uses probabilities– Advantage: can use evolutionary models.
Fig. 26-11
TAXA
Lanc
elet
(out
grou
p)
Lam
prey
Sala
ma n
der
Leop
ard
Turt
le
Tuna
Vertebral column(backbone)
Hinged jaws
Four walking legs
Amniotic (shelled) egg
CH
AR
AC
TER
S
Hair
(a) Character table
Hair
Hinged jaws
Vertebralcolumn
Four walking legs
Amniotic egg
(b) Phylogenetic tree
Salamander
Leopard
Turtle
Lamprey
Tuna
Lancelet(outgroup)
0
0 0
0
0
0
0 0
0
0
0 0
0 0 0 1
11
111
1
11
1
1
11
11
Sequentially group taxa by shared derived character states (apomorphies)
Fig. 26-8b
3
4
DNA sequence data - alignment
Each nucleotide position = CharacterCharacter states = specific nucleotide
Homology
• Similarity resulting from common ancestry.
– E.g., the forelimb bones of a bird, bat, and cat.
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.
Both examples of reversal within Tetrapods: loss of a derived feature – forelimbs.
Leg-less lizards Snake
Example of convergence relative to one another!Independently evolved.
snakesleg-lesslizards
leggedlizards
**
*= loss of legs
gain of legs (Tetrapods)
Fig. 26-18
(b) Paralogous genes
(a) Orthologous genes
Ancestral gene
Paralogous genes
Ancestral species
Speciation withdivergence of gene
Gene duplication and divergence
Species A after many generations
Species A Species B
Species A
Orthologous genes
Orthology – genes homologous
Paralogy – genes not homologous
Gene Duplicationcan occur!
Monophyletic Group
• a group consisting of: – a common ancestor +– all descendents of that common ancestor
Fig. 26-13
Drosophila
Lancelet
Zebrafish
Frog
Human
Chicken
Mouse
CENOZOIC
Present65.5
MESOZOIC
251Millions of years ago
PALEOZOIC
542
One can date divergence times with molecular clock and fossils
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.
C B F E D A
Is “E” more closely related to “D” or to “F”?Is “E” more closely related to “B” or to “A”?Is “E” more closely related to “B” or to “C”?
C B F E D A
Is “E” more closely related to “D” or to “F”?Is “E” more closely related to “B” or to “A”?Is “E” more closely related to “B” or to “C”?
Answers: F, B, neither (equally to “B” & “C”)
Paraphyletic group
• Consist of common ancestor but not all descendents
• Paraphyletic groups are unnatural, distort evolutionary history, and should not be recognized.
We are human, butwe are also apes.
• We share unique human features.
• We also share features with other apes (and with other animals, plants, fungi, bacteria, etc.).
• Humans didn’t evolve from apes, humans are apes.