Lecture 9: Evolution

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Lecture 9 Evolution Classification

• Because of how evolution occurs Hierarchical,
  nested classification is natural
• There is ONE TRUE PHYLOGENY
• Based on interrelationships
• Life started at one point diverged

Speciation
Origin
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Study of Evolutionary History

• Taxonomy classification (naming)
• Systematics describes evolnry relationships
• Assume similarity in heritable characters
  signifies closeness of relationship
• Use characters to deduce relationships classify

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Types of Taxonomy

• Phenetic
• Groups species by phenotypic similarity
• May use physical, immunological, or genetic
  traits
• Phylogenetic
• Use evolutionary relationships
• How recently shared common ancestor
• Phenetic phylogenetic taxonomy often give
  similar results
• More on this next class

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Terminology

• Evolution occurs in two ways
• Anagenesis directional change in a lineage
• Cladogenesis branching by speciation
• Rate pattern of anagenesis branching pattern
• True Phylogeny

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Reconstructing Phylogenies

• Use
• Ancestral Character (Plesiomorph)
• Primitive
• Inherited with little or no change from ancestor
• Derived Character (Apomorph)
• Recently changed

Only CHARACTERS are PRIMITIVE, not SPECIES
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Reconstructing Phylogenies

• Use Shared Characters
• Because of PARSIMONY
• (smallest number of changes in phylogeny)
• Change takes time
• Change is unlikely
• Shared characters usually indicate close
  relationships

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Shared Characters

• Ancestral Homologies
• Character found in both taxa
• Character found in common ancestor
• Character not in all descendants
• Derived Homologies
• Character found in both taxa
• Character found in common ancestor
• Character in all descendants of common ancestor

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• 3. Analogies
• Characters have no common history
• Characters are not in common ancestor
• Characters developed independently
• CONVERGENCE
• May be evolutionary reversals to ancestral state
• - cause loss of info about relationships

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A A A A
A A A A
A
A
A
A
A
A
A
Derived Homology Ancestral Homology
Analogy - character A - character A -
character A
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More realistic example
abcdef abcdef abcdef abcdef abcdef
f
e
d
c
a
b
a ancestral a derived
abcdef
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Phylogenetic Groupings

• Monophyletic
• Shared derived homologies
• Contains all the descendants of a common ancestor
• e.g. all birds
• Paraphyletic
• Shared ancestral homologies
• Species with derived characters not included
• Some but not all descendants of a common ancestor
• e.g. fish reptiles missing birds, mammals

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• 3. Polyphyletic
• Analogies
• Common ancestor not in group
• Shared characters evolved independently
• e.g. vultures

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Groupings
A A A A
A A A A
A
A
A
A
A
A
Monophyletic Paraphyletic
Polyphyletic
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Phylogenetic Reconstruction Whales

• Sea-dwelling 53.5 mya
• Descendants of Artiodactyla (even-toed ungulates)
• Rudimentary vestigial characters common to
  land mammals (pelvic girdle, diaphragm, sensory
  structures)
• Intermediary fossils Ambulocetus the walking
  whale (47 mya)

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Whale Phylogeny continued

• Paraxonic foot symmetry characteristic of
  artiodactyla (axis passes b/w 3rd/4th digits)
• Molecular studies closest to artiodactyla out of
  48 mammals
• Not just related to artiodactyls they ARE
  artiodactyls
• Geochemical studies move from FW to SW in tooth
  oxygen ratios

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• Recent evidence hippos more closely related to
  whales than other artiodactyla

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