SYSTEMATICS
• The reconstruction and study of
evolutionary relationships
Taxonomy
• Two main objectives:
– to sort out organisms into species
– to classify species into higher taxonomic levels
• Species that appear to be closely related are grouped
into the same genus.
• the leopard, Panthera pardus, belongs to a genus
that includes the African lion (Panthera leo) and the
tiger (Panthera tigris).
• Taxon = a named taxonomic unit at any
level; (taxa = plural)
– ex: Mammalia is a taxon at the Class level
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Did
King
Phillip
Domain
Eukarya
Kingdom
Animalia
Phylum
Chordata
Subphylum
Vertebrata
Come
Class
Mammalia
Over
For
Great
Sex?
Order
Rodentia
Family
Sciuridae
Genus
Sciurus
Species
Sciurus
carolinensis
Sciurus
carolinensis
TAXONOMY
• taxonomic system developed by Linnaeus in
the 18th century
– binomial = Genus species
– classification system
•
•
•
•
•
•
•
•
Domain
Kingdom
Phylum
Class
Order
Family
Genus
species
Eukarya
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
sapiens
Limitations of the Linnean System
Many hierarchies are being re-examined based on
the results of molecular analysis
-Linnaean taxonomy does not take into account
evolutionary relationships
-The phylogenetic and systematic revolution is
underway
5
PHYLOGENY
• Hypothesis of the evolutionary history of a
group
• represented by pictures: phylogenetic trees
– time goes from the bottom up
– read from bottom up, NOT LEFT TO RIGHT
– branch “length” = the number of changes
Fig. 23.1
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Variations of a Cladogram
Gibbon Human
Chimp Gorilla Orangutan
Gibbon Orangutan Gorilla Human
1
1
2
2
Chimp
3
1
Version 1
2
3
3
Version 2
Human
Gorilla
Orangutan
Gibbon
Version 3
a.
Chimp
b.
Reproduced by kind permission of the Syndics of Cambridge University Library, Darwin’s Notebook ‘B’, ‘Tree of Life’ Sketch, p. 36 from
DAR.121 D312
Phylogenies depict evolutionary relationships
11
• Phylogenetic trees reflect the hierarchical classification
of taxonomic groups nested within more inclusive
groups.
Fig. 25.8
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Approaches to Constructing
Phylogenies
• Cladistics
– uses shared derived characteristics
(synapomorphies) to classify organisms
– Not shared ancestral characteristics
(symplesiomorphies)
– not overall similarity
• Because evolution is not steady paced, not
unidirectional, may be convergent
Cladistics
Examples of ancestral versus derived characters
• Presence of hair is a synapomorphy (shared
derived feature) of mammals
• Presence of lungs in mammals is a
symplesiomorphy (an ancestral feature); also
present in amphibians and reptiles
14
Building Cladograms
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Traits:
Organism
Jaws Lungs
Amniotic
Membrane
Hair
No Tail Bipedal
Lamprey
0
0
0
0
0
0
Shark
1
0
0
0
0
0
Salamander
1
1
0
0
0
0
Lamprey
Shark
Salamander Lizard
Tiger
Gorilla Human
Bipedal
Tail loss
Lizard
1
1
1
0
0
0
Tiger
1
1
1
1
0
0
Gorilla
1
1
1
1
1
0
Hair
Amniotic
membrane
Lungs
Jaws
Human
a.
1
1
1
1
1
1
b.
Can also use molecular data
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
DNA Sequence
Outgroup
Site
1
2
3
4
5
6
7
8
9
10
Species A
G
C
A
T
A
G
G
C
G
T
Species B
Species D
Species A
8:T
Species B
Species C
Species D
A
G
A
C
C
C
A
A
A
G
T
T
C
A
C
C
G
G
G
G
G
C
T
T
A
G
G
T
4:T
G
8:T
C
10:T
T
G
2:T
Outgroup
A
T
A
T
C
C
G
T
A
T
C
G
6:C
G
9:A
G
Species C
C
1:A
G
5:C
A
Homoplastic
evolutionary
changes
Homologous
evolutionary
changes
PHYLOGENY
• systematists prefer monophyletic taxa
– a single ancestor gave rise to all species in that
taxon and to no species in any other taxa
Systematics and Classification
Monophyletic Group
18
Systematics and Classification
Paraphyletic Group
19
Systematics and Classification
Polyphyletic Group
20
Systematics and Classification
Old plant classification system
21
Systematics and Classification
New plant classification system
22
Evidence used to reconstruct
phylogenies
• Comparative anatomy, morphology,
embryology, etc.
– problems of homology vs homoplasy (analogy)
• homology = likeness due to common ancestry
• homoplasy or analogy = likeness due to convergent
evolution
Fig. 23.9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
SCIENTIFIC THINKING
Question:
How many times have saber teeth evolved in mammals?
Hypothesis: Saber teeth are homologous and have only evolved once in mammals (or, conversely, saber teeth are
convergent and have evolved multiple times in mammals).
Phylogenic Analysis: Examine the distribution of saber teeth on a phylogeny of mammals, and use parsimony to infer the
history of saber tooth evolution (note that not all branches within marsupials and placentals are shown on the phylogeny).
Saber-toothed
nimravid
Saber-toothed
nimravid
Hyenas
Saber-toothed
cat
Civets
Mongooses
Phylogeny of Carnivores
Bears, seals,
weasels, canids,
and raccoons
Carnivores
Saber-toothed
marsupial
Phylogeny of Mammals
Felines
Marsupials
Placentals
Nimravids
Monotremes
Carnivores
Result: Saber teeth have evolved at least three times in mammals: once within marsupials, once in felines, and at least once in a group of now-extinct cat-like
carnivores alled nimravids.
Interpretation: Note that it is possible that saber teeth evolved twice in nimravids, but another possibility that requires the same number of
evolutionary changes (and thus is equally parsimonious) is that saber teeth evolved only once in the ancestor of nimravids and then
were subsequently lost in one group of nimravids.
(Note that for clarity, not all branches within marsupials and placentals are shown in this illustration.)
Can Have
Homoplastic Molecular Data
A Cladogram: DNA
28
Evidence used to reconstruct
phylogenies
• Protein comparisons
• DNA comparisons
– DNA-DNA hybridization, restriction mapping,
DNA sequencing
Character Mapping
• Once you have a phylogeny you can trace
the evolution of characters or traits in that
group
• use the rules of parsimony
– the simplest is the best
Parental Care
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a.
b.
a: Image #5789, photo by D. Finnin/American Museum of Natural History; b: © Roger De La Harpe/Animals Animals
Parsimony and Homoplasy
33
Classification System
35
Opisthokonta
Amoebozoa
Excavata
Archaeplastida
Rhizaria
Chromalveolates
Archaea
Eubacteria
Six Supergroups Within Eukarya
•Excavata (organisms lacking typical mitochondria)
•Chromalveolata (organisms with chloroplasts obtained through
secondary endosymbiosis)
•Archaeplastida (organisms with chloroplasts for photosynthesis)
•Rhizaria (organisms with slender pseudopods used for movement)
•Amoebozoans (organisms with blunt pseudopods used for movement)
•Opisthokonts (fungi, animal ancestors, and animals)
Grouping Organisms
Carl Woese proposed a six-kingdom system
Prokaryotes
Eukaryotes
38
KINGDOMS
• Monera = Archaebacteria & Eubacteria
– prokaryotic
• Protista
– eukaryotic
• Plantae
– eukaryotic, multicellular, autotrophic, cell walls
• Fungi
– eukaryotic, multicellular, heterotrophic, cell walls
• Animalia
– eukaryotic, multicellular, heterotrophic, no cell walls