BI111 Lecture Notes - Lecture 8: Boletus Edulis, Convergent Evolution, Polyphyly
BI111 – L8
Cladistic Phylogenies Based on:
Principle of monophly - all groups in a clade includes a common ancestor and all of its
descendants, based on idea of nesting,
oMonophyletic taxon: includes an ancestral species and all of its descendants
oPolyphyletic taxon: includes species from different evolutionary lineages
oParaphyletic taxon: includes an ancestral species and only some of its descendants
Principle of parsinomy (Occam’s razor) - simplest explanation most likely to be correct, unless
other data suggest more complicated explanation
oAll phylogenetic trees are a hypotheses that attempt to accurately reflect historical
events, speciation and divergence that has happened through history
oEx. It is most likely that hair evolved once and has been passed on (simplest explanation)
oEvolutionary change is an unlikely event:
Evolution of character twice is extremely unlikely
Evolutionary trees with derived characters appearing once are most
parsimonious
oEx. despite phenotypic similarity of pitchers (plant), most morphological, developmental
and genetic data shows differences between the old-world and the new-world pitcher
plants
Convergent evolution is more parsimonious explanation
Many Ways to Depict Phylogenetic Relationships
Depends on what data is available
oMore info/characters allow better resolution of specifications (bifurcations)
Rooted vs. Unrooted
oRooted phylogeny: past → future (left to right)
oUnrooted: not sure where the ancestral relationships are, free form
If seen a line with a given unit = tells how distant the descendants are
Scaled vs. Unscaled
oScaled
oUnscaled
Constructing a Cladogram:(refer to slideshow)
1. Complete character table of 6 taxa, 4 traits (presence/absence)
2. Determine outgroup
3. Set outgroup values to 0, and recode all others to 0 (if same) or 1 (if different)
4. Construct cladogram based on shared derived characters
Phylogeny, Plants, and Plant Body’s
Molecular Characters:
Allows the independent testing of evolutionary hypotheses based on fossils
Molecular character advantages:
oAbundant data
oEasier comparison of distant or very close relations
Molecular character disadvantages:
oOnly 4 states in nucleotides, 20 in amino acids
oBase changes may have evolved independently
We can look at sequence alignment and compare them to create a phylogenetic tree
Phylogeny and alignment of three unnamed species discovered in a commercial packet of dried
porcini
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
It is most likely that hair evolved once and has been passed on (simplest explanation: evolutionary change is an unlikely event: Evolutionary trees with derived characters appearing once are most parsimonious: ex. despite phenotypic similarity of pitchers (plant), most morphological, developmental and genetic data shows differences between the old-world and the new-world pitcher plants. Depends on what data is available: more info/characters allow better resolution of specifications (bifurcations) Rooted vs. unrooted: rooted phylogeny: past future (left to right, unrooted: not sure where the ancestral relationships are, free form. If seen a line with a given unit = tells how distant the descendants are. Allows the independent testing of evolutionary hypotheses based on fossils. Molecular character advantages: abundant data, easier comparison of distant or very close relations. Molecular character disadvantages: only 4 states in nucleotides, 20 in amino acids, base changes may have evolved independently. We can look at sequence alignment and compare them to create a phylogenetic tree.
