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EVOLUTIONBiology 145
Lecture 11 –Classification
Goals of Classification
1) Organization of complex data sets
2) Elucidation of underlying evolutionary history
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Taxonomy
Carl Nilsson Linnæus
Kingdom: Animalia
Phylum (35) Chordata
Class (15) Mammalia
Order (29) Carnivora
Family (16) Canidae
Genus (10) Canis
Species ( 5) Canis lupus
Homo sapiens sapiens (Linneaus, 1758).
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C. lupus C. simensis C. latrans C. aureusLycaonpictus
GENUS: Canis GENUS: Lycaon GENUS: Hyaena
Hyaena hyaena
FAMILY: HyaenidaeFAMILY: Canidae
ORDER: Carnivora
CLASS: Mammalia
C. lupus lupus
C. lupus lycaon
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Phenetic methods of phylogenetic reconstruction
Based on the degree of similarity between taxa, ‐molecular, phenotypic, or anatomical. A tree‐like network expressing phenetic relationships is called a phenogram
Phenetics can be subjective
CLADISTICS
Groups taxa according to COMMON ANCESTRY.
A speciation event creates two SISTER species
Branching diagram is called a CLADOGRAM
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Cladistics uses SHARED, DERIVED CHARACTERS (homologies)
A correct cladogram is MONOPHYLETIC ( includes all descendants of the common ancestor)
Ambiguous characters
HOMOLOGIES versus HOMOPLASIES(shared, derived (not in common functions may vary) ancestor)
Ulna (etc.) is a homologous structure
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Taxonomic level is important:
Wings of birds and bats at HOMOLOGIES at level of CLASS (pentadactyl limbs in the common ancestor of bats and birds)
Wings of birds and bats at HOMOPLASIES at level of PHYLUM (no wings in common ancestor to all Chordates)
HOMOPLASIES are often the result of CONVERGENT EVOLUTION,
HOMOLOGIES are the result of SHARED ANCESTRY
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Characters may have POLARITY
Mexican blind cave fish, Astyanax mexicanus
Distant chordate ancestor – NO EYES
A. fasciatusancestor –EYES
Mexican cave fish– NO EYES
What is the ancestral number of chaetae? Have chaetae been lost or gained? What is the POLARITY?
Solution is to use an OUTGROUP
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Lancelet (Cephalochordate)
Molecular characters
Probabilities of HOMOPLASIES and REVERSALS quite high
ACC AGC ACC
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Protein sequences show fewer homoplasies than DNA sequences because we have 20 amino acids versus only 4 nucleotide bases.
Cytochrome C enzyme has 104 amino acids
Molecular systematics is STATISTICAL and requires large data sets
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TIME
The TIME axis can be scaled using:
1) The Fossil Record
2) The rate of molecular (DNA, rNA, or protein) change
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The Tree of Life
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