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EVOLUTION AND SYSTEMATICS
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http://evolution.berkeley.edu/evolibrary/article/evo_01
UNDERSTANDING PHYLOGENY
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UNDERSTANDING PHYLOGENY
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MISCONCEPTIONS
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Evolution produces a pattern of relationships among lineages that is tree-like, not ladder-like.
MISCONCEPTIONS
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There is no correlation with level of "advancement."
MISCONCEPTIONS
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For any speciation event on a phylogeny, the choice of which lineage goes to the right and which goes to the left is arbitrary.
MISCONCEPTIONS ABOUT HUMANS
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Humans did not evolve from chimpanzees.
Humans are not "higher" or "more evolved" than other living lineages.
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CLADE= MONOPHYLETIC
POLYPHYLETIC POLYPHYLETIC
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Clades are nested within one another — they form a nested hierarchy
BUILDING THE TREE Characters
heritable traits Comparable across organismsMorphology, behavior, genetic sequences
Homologous characters
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SYNAPOMORPHIES
Basis for grouping taxa together becausethey represent the product of aunique evolutionary event
Convergence - Stem succulence and “spines” in Cactaceae and Euphorbia spp.
Selection of OUTGROUP Coding of Characters
0- ancestralNon-zeros- derived character
Reconstruction of phylogenyParsimony analysis
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PRINCIPLE OF PARSIMONY
The cladogram that is shortest – has the fewest number of steps (character state changes) – is
accepted as most probable,
because it minimizes the number of ad hoc hypotheses.
“Entia non sunt multiplicanda praeter necessitatem.”
(That does not exist which multiplies more than necessary.)
Of two or more competing hypotheses, the simplest one is accepted.
EXAMPLE1 2 3 4 5
A 1 1 1 1 1
B 1 0 0 0 0
C 0 0 1 1 1
OUTGROUP
0 0 0 0 0
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Strict consensus of 2,023 equally parsimonious trees
894 evolutionary steps CI = 0.50 RI = 0.66
OUTGROUP
100%
Ophiorrhizeae
Urophylleae
90%
74%
Antherostele100%
Morphology of Antherostele• subsessile inflorescence • simple dichasium cyme• inserted at leaf axils• flowers unisexual (dioecious)• Sweet-scented• Rudimentary parts present
style
stigma
Female flower Male flower