Transcript Systematics and Phylogeny

Phylogeny and the Tree of Life
Chapter 26
BCOR 012
February 4,7, 2011
Outline for February 4,7 2011
Systematics: Connecting Classification to Phylogeny
Systematics, Taxonomy, and Phylogeny
Constructing cladograms
Phylogenetic Classification
Molecular Systematics
Parsimony
Systematics is the study of biological diversity
in an evolutionary context. It includes
•speciation
•taxonomy
•phylogeny.
Taxonomy is the branch of systematics concerned
with naming and classification.
• Scientific names are binomials
Carolus Linnaeus
• Example: Acer saccharum
1707-1778
- Acer is the genus name - it is a Latin noun
- saccharum is the specific epithet - it is a Latin
adjective
Biological
classifications are
hierarchical: each
taxonomic group is
nested within a
more inclusive
higher order group.
(Note that only the genus name
and specific epithet are italicized.)
Fig. 26-4
Order
Family Genus
Species
Taxidea
Taxidea
taxus
Lutra
Mustelidae
Panthera
Felidae
Carnivora
Pantherap
ardus
Lutra lutra
Canis
Canidae
Canis
latrans
Canis
lupus
Phylogeny and Classification
“Our classifications
will come to be, as
far as they can be
so made, genealogies.”
- Charles Darwin, 1859
Phylogeny is the study of the
pattern of divergence history.
(as opposed to speciation, which
addresses process.)
Assembling a phylogeny
using cladistics, taxa are
associated on the
basis of shared evolutionary
innovations.
Willi Hennig, 1913 - 1976
Founder of Phylogenetic
Systematics
(also called cladistics)
One of the evolutionary
innovations shared by birds
is the feather …
Homology, the sharing of an innovation (derived
character) because of its invention in a common ancestor
Serial Homology of the Lobster
Figure 34.4b-c Chordate segmentation
CRUSTACEANS COMPARED - EVOLUTIONARY HOMOLOGY
CRUSTACEANS COMPARED:
EVOLUTIONARY TRANSFORMATION
ROCK CRAB
LOBSTER
Fig. 26-8
1
Deletion
2
Insertion
3
4
Fig. 26-8a
1
Deletion
2
Insertion
Fig. 26-8b
3
4
DNA Evolution: stable and labile characters relate to function.
Example: Homeobox genes, which govern variation in serial
homologs.
The homeobox (in the gene) codes for a homeodomain (in the
protein synthesized from the gene). The homeodomain has a
precise three-dimensional structure related to its function.
In evolution, the
homeodomain is
relatively stable
because it has a
precise job.
Amino acid
sequences
compared
for the
homeotic
gene Ubx
insects
arthropods
Dm - Fruitfly
Tc - Beetle
Jc - Butterfly
Ak - Onychophoran
Decides six legs or more
Parsimony
Under the principle
of parsimony, tree A
would be
preferred over B and
C as it is one step
shorter.
Ockham's razor.:
when trying to
choose between
multiple
competing theories
the simplest theory
is probably the
best.
How to construct a cladogram:
•
•
•
•
•
Choose a study group
Choose an appropriate outgroup
Compile data matrix
Polarize characters
Use shared derived characters to associate
study group taxa and construct the
cladogram
The outgroup is the group used to polarize character
states in the study group. It should be the group
most closely related (on the basis of other lines of
evidence) to the study group that is not actually part
of the study group.
lancelet
How to construct a cladogram:
•
•
•
•
•
Choose a study group
Choose an appropriate outgroup
Compile data matrix
Polarize characters
Use shared derived characters to associate
study group taxa and construct the
cladogram
The primitive character is the one shared by the outgroup and
some, but not all, of the study group.
How to construct a cladogram:
•
•
•
•
•
Choose a study group
Choose an appropriate outgroup
Compile data matrix
Polarize characters
Use shared derived characters to associate
study group taxa and construct the
cladogram
Kinds of Characters
• Apomorphy - a derived character state
• Synapomorphy - a shared derived
character state
• Autapomorphy - a derived character state
unique to one study group member
• Symplesiomorphy – a shared primitive
character state
Cladistic Analysis and
Classification: Kinds of Groups
A monophyletic group includes a common ancestor and
all of its descendents
Example: Reptilia (defined to include birds)
A paraphyletic group includes a common ancestor and some
but not all of its descendents
Example: Reptilia (defined to exclude birds)
A polyphyletic group is a group whose members do not share
a recent common ancestor
Example: homeotherms (warm-blooded animals)
For Phylogenetic Classification, taxa
(taxonomic groups) should be natural groups,
that is groups reflecting phylogeny.
In a phylogenetic classification, only
monophyletic groups are named.
If a paraphyletic group bears a name, it will
be an informal one (e.g., ‘gymnosperms’)
The nested relationship of clades is reflected in the
nested relationship of taxa in the resultant
classification. All are monophyletic groups.
EUKARYA
eukaryotes
Dinoflagellates
Forams
Ciliates Diatoms
Red algae
Land plants
Green algae
Cellular slime molds
Amoebas
Euglena
Trypanosomes
Leishmania
Animals
Fungi
Sulfolobus
Green nonsulfur bacteria
Thermophiles
Halophiles
(Mitochondrion)
COMMON
ANCESTOR
OF ALL
LIFE
Methanobacterium
ARCHAEA
both are prokaryotic
Spirochetes
Chlamydia
Green
sulfur bacteria
BACTERIA
Cyanobacteria
(Plastids, including
chloroplasts)