Outgroups Outgroups are the most common method for rooting trees Outgroup criteria 1. “Outside”...
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Transcript of Outgroups Outgroups are the most common method for rooting trees Outgroup criteria 1. “Outside”...
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Outgroups
• Outgroups are the most common method for rooting trees
• Outgroup criteria1. “Outside” the group of study2. Closely related enough to be informative
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• Outgroup Rule: Character states shared by the outgroup and some of the ingroup are likely plesiomorphic
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Build the tree with cladistics
CharactersTaxa 1 2 3 4 5Outgroup 0 0 0 0 0A 1 0 0 0 1B 1 1 0 1 0C 1 0 1 1 0
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Fig. 26-UN5Draw the tree using cladistics…
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Fig. 26-UN10a
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If character conflict occurs, pick the correct tree based on the principle of parsimony
12 changesCharacter 3 evolves twiceCharacter 2 evolves once and is lost
11 changesCharacter 10 evolves once and is lost
10 variable binary characters, minimum number of steps = 10
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Problems in tree building
Character conflict
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Good synapomorphies
• Homology = similarity in form or function shared by organisms because the feature was found in their common ancestor
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Misleading Characters
• Homoplasy = “false homology”
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Which lineages are endotherms?
The most parsimonious explanation is that endothermy arose twice:Convergence
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Mammal tree article
Convergence in mammals (easier to ID for marsupials vs. placentals)—similar ecological niches
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DNA data (right) has turned conventional mammal taxonomy (left) on its head. Morphological analyses were mislead by convergence.
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Mapping character state changes onto a tree
2 independent gains of echolocation (convergence) or 1 gain followed by one loss (character state reversal)?Which do you consider more likely?