BIOLOGY 1B Lecture Notes - Lecture 6: Willi Hennig, Paraphyly, Polyphyly
11 Jun 2018
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Lecture 6: Phylogenetic Systematics
9/6
• Trees of life: metaphor for life or the universe; models of trees; universal metaphor
o Darwin’s tree
• Extent lineages: modern lineages that are alive now; top of darwins tree
• Heckel’s tree: tree with man on top, bacteria on base
o Phylogeny- Pedigree of man
o Problematic bc man is on top
o Bacteria at base of tree
o Teleology: goal oriented process in evolution of tree
▪ Evolution is or is not oriented?
• Six kingdom system: fungi, Animalia, plantae, bacteria, archaea, protista
o Linnaeus: 2 kingdom system of animals and plants= problematic
▪ Fungie is different from plants; closer related to animals
▪ Prokaryotes were being better studied, bacteria and archae are much different from each
other
• Cladogram of Life:
o three major groups: bacteria, eukarya, archaea
• Linnaen ranking system: ranks life, domain, kingdom etc.
o Not useful
• Willi Hennig: argued and wrote about need for new way to classify organisms
o Cladistics: phylogenetic systematics
o Classification based on evolutionary history
o Taxa are defined by common ancestry
▪ Diagnose by shared characteristics
o A cladogram is a branching diagram of hypothetical evolutionary relationships
• Cladogram reading:
o Taxa at top of branches
o 2 taxas shared by one NODE called SISTER TAZA
o NODE is represented by a speciation event
o BASAL NODE is the most recent common ancestor
o Look at picture on lecture slides
• Synapomorphies
o Character analysis
o Tick mark represents synadomarks= shared characteristics
▪ Limbs are a synadomorphy
▪ Wings
▪ Gelatinous eggs
• Natural and unnatural group
o Monophyly= natural group, common ancestor and all descendants
o Paraphyly= excludes some descendants= unnatural
▪ Doesn’t deserve proper name in biology
o Polyphyly= includes branch tips of ancestors but excludes ancestors
• Taxonomic definition and diagnoses
o Crown group- all descendants same ancestor
▪ Includes distal groups on taxa, the common ancestors, not including stem taxa leading up
to common ancestors- node based
o Stem based definition: look at ancestors beyond node of common ancestor
o Apomorohy-based approach: focus on synapomorphies
• Monkey example of paraphyly
o All monkey descendants aren’t called “monkey”
• Ex. of paraphyly: Birds are descendants of nonavian dinosarus
o Reptilia leaves out birds as a descendant; doesn’t include all descendants
• Polytomy: an internal node that has more than two immediate descendants; not fully resolved; “start tree”
• How do we build robust cladograms?
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