Cladistics
Professor Andrea Garrison
Biology 3A
Illustrations ©2014 CENGAGE Learning
Cladistic analyses
• Phylogenetic groups are called clades
• Phylogenetic trees group organisms into
clades considered truly monophyletic
– Molecular evidence more important than
morphological evidence
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Cladistic analyses
• Cladistics focuses on how traits as they evolve
from ancestors to their descendants
• Traits considered ancestral or derived
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Cladistic analyses
Ancestral vs. derived characters
• Ancestral character (state)
– Found in ancestral species of a clade
– May change via natural selection
over time
– Give rise to derived character (state)
– Ex: fins found in early vertebrates
• Derived character (state)
– New in a descendent species
– Ex: limbs found in later vertebrates
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Cladistics analyses
Ancestral vs. derived characters
• Fossil record often helps distinguish ancestral and derived characters
– Oldest fossils have ancestral characters
– Characters that show up in younger fossils are derived
• If no fossil record, compare “ingroups” with “outgroups”
– Ingroup is the clade being studied
– Outgroup is the closely related species not part of the clade
• Determined using morphology, fossil record, embryology, gene sequencing
– Characters found in outgroup are ancestral, characters found in
ingroup and not outgroup are derived
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Outgroup Comparison
A. Caddis fly
(Limnephilidae)
B. Orange palm dart butterfly
(Cephrenes auglades)
C. Monarch butterfly
(Danaus plexippus)
Monarch butterflies have four legs.
Most butterfly species have six legs.
Most insects have six legs.
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Figure 24-10, p. 539
Cladistic analyses
• A derived character is called an apomorphy
(apo = away from; morphe = form)
• A derived character found in more than one
species is called a synapomorphy (syn =
together)
– Indication that these species may be members of
the same clade
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Cladistics analyses
• Phylogenetic trees group together species that share derived
characters (synapomorphies)
• Phylogenetic tree illustrates the hypothesized sequence of
evolutionary branching that produced the organisms under study
• A common ancestor is hypothesized at each node
– every branch is a strictly monophyletic group
– shared derived characters that define each clade sometimes listed on the
branches
• Molecular research provides huge database
– Maximum parsimony (Occam’s razor)
• Use simplest plausible explanation
– Statistical approach (maximum likelihood)
• Use what we know about frequency of certain genetic mutations, etc.
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Phylogenetic tree
hypothesizing
only 5
evolutionary
changes is more
parsimonious
than the tree with
10 evolutionary
changes
Cladistics analyses
• Cladogram is a branching diagram
showing evolutionary
relationships
• Endpoints represent different
species or clades of organisms
• Does not show time
• Does not show how ancestors
related to descendants or how
much change has occurred
• Each node represents hypothetical
ancestor
• Try to avoid analogous traits
developed through convergent
evolution
• Used as basis for phylogenetic
trees
Cladistics; illustration by Alexei Kouprianov ;
http://creativecommons.org/licenses/by-sa/3.0/legalcode
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Cladistics analyses
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