Lecture 14: Reconstructing Phylogenies

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Lecture 14 Reconstructing Phylogenies

• 1) homoplasy (analogy) character not present in
  RCA
• - convergent evolution
• - parallel evolution
• 2) homology character inherited from CA
• a) ancestral (symplesiomorphy)
• - little change from distant ancestor
• b) derived (synapomorphy)
• - recent change

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Homology vs. Analogy

1. Same fundamental structure
2. Same relationship to surrounding characters
3. Similarities in embryology

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Embryology

• Haeckels (1886) biogenetic law
• ontogeny recapitulates phylogeny
• each embryonic stage adult stage
• of ancestor
• WRONG!
• Von Baers (1828) law
• among related spp., early stages are more similar
  than later stages
• examination of early devt can reveal close
  relationships

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Examples
Successive stages of vertebrate embryos

• Cattle metacarpals
• start off separate fuse
• during development
• Anteaters teeth present early in development
  resorbed

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Von Baers Law

• Sometimes useful to distinguish b/w ancestral
  derived traits, not always
• e.g. fused cannon bone derived
• toothlessness in Edentates derived
• But, early stages may be special adaptations
• - beak of tadpole
• - milk teeth of bats
• - cotyledons in plants

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• terminal stages of ancestors ontogeny may be
  lost
• e.g. paedomorphosis
• (retention of juvenile characters in adult)
• - in salamanders is derived, not ancestral

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Reconstruction continues

• distinguish homologies from analogies
• distinguish ancestral homologies from derived
  homologies
• - need to determine polarity of change (ancestral
  ? recent)

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Strategies to Distinguish b/w Ancestral Derived

• 1) morphocline or transformation series
• e.g. chromosome inversions in Drosophila
• ABCDEFG ? AEDCBFG ? AEDFBCG
• - can infer sequence, but which is ancestral?
• a ? b

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Outgroup Analysis

• outgroup taxon that diverged from a group
  before they diverged from each other
• principle of parsimony fewest changes
• consider 3 spp outgroup sp.
• - 1 character, 2 states
• sp. 1 b
• sp. 2 b
• sp. 3 a
• sp. O a

A B C D
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2 hypotheses 1 a ? b (a ancestral b
derived) 2 b ? a (b
ancestral a derived)
the character state present in the outgroup is
assumed to be ancestral
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Butterflies

• brush-footed, monarchs ? 2 reduced legs
• swallowtails, sulphurs ? 6 functional legs
• which state is ancestral ?
• Moths diverged from butterflies before they
  diverged from each other (moths outgroup)
• moths ? 6 functional legs
• most parsimonious 6 functional legs ancestral

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5 Characters

• Character 1
• shared by A, B, C
• (synapomorphy)
• separates them from
• outgroup

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• Character 2
• unique derived trait in taxon B
• no info about relationships
• Character 3
• unique derived trait in taxon C
• no info about relationships

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• Character 4
• synapomorphy
• unites B C
• Character 5
• unique derived trait in taxon A
• no info

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• Fused cannon bones in cattle
• Toothlessness in adult anteaters
• Derived traits b/c
• unfused metacarpals adult teeth are widespread
  in other mammals

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Primitive characters

• primitive condition in an ingroup is that which
  is found in outgroups
• Common characters are not necessarily primitive!
• Often true owl monkeys are only nocturnal
• primate nocturnal habit is derived
• However

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Primitive vs. Derived

• Few vertebrates lack jaws, but jawlessness in
  lampreys is primitive, not derived
• Distribution, not number of spp. with the trait,
  is important

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Complete Fossil Record

• Can aid in analysis
• e.g. Progressive reduction in of digits in
  horses
• one-toed condition is derived
• same info from outgroup analysis rhinos
  tapirs
• But

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Litopterna

• Extinct horse-like mammals
• 3 toed observed later than
• 1 toed
• Outgroup analysis necessary
• In fact, more detailed fossil record shows
• 3 toed both before after 1 toed