cladistics - systematics
TRANSCRIPT
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Systematics, then, is no less than understanding the history of all life.
-Diana Lipscomb, 1998
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CLADISTICS
LIWALUG, MUSLIMA P.MIB1
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Method that groups organisms that share derived characteristics
The value or form of a feature is referred to as a character state
Relationships are portrayed in straight line diagrams
Phylogenetic Systematics
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HOMOLOGY• traits have common
ancestry• may/may not share
function• may/may not look alike
HOMOPLASY• traits are similar
because of convergent evolution
ANALOGY• traits with common
function• may/may not share
ancestry• may/may not look
alike
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Synapomorphies• is a trait that is shared by 2 or more taxonomic groups• is derived through evolution from a common ancestral
form
Plesiomorphic• ancestral state• character state that a taxon is inferred to have been
retained from its ancestors
Apomorphic• derived state• can be used to diagnose a clade – or even to define a
clade name in phylogenetic nomenclature
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Cladistic Analysisby Willi Hennig (1966)
is to determine which character states are primitive and which are derived based on common ancestry
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Principles
Parsimony – states that any hypothesis that requires fewer assumptions is a more defendable hypothesis
Occam’s Razor - one should not make more assumptions than the minimum needed to explain anything
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A B
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Cladogram
is an evolutionary tree which shows evolutionary relationships by showing points at which lineages diverged from common ancestral forms
is constructed such that the number of changes from one character state to the next is minimized
is interpreted as that which requires the fewest evolutionary changes in the taxa involved
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Clade
a group of two or more taxa that includes both their common ancestor and all their descendants
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FOUR LIMBS WITH DIGITS
Tetrapoda clade1
Amniota clade2
Reptilia clade3Diapsida clade4
Archosauria clade5
EMBRYO PROTECTED BY AMNIOTIC FLUID
OPENING IN THE SIDE OF THE SKULL
SKULL OPENINGS IN FRONT OF THE EYE & IN THE JAW
FEATHERS & TOOTHLESS BEAKS.
SKULL OPENINGS BEHIND THE EYE
DERIVED CHARACTER
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Node - a branch points based on homologous, shared derived traits
Root - the common ancestor of all taxa Branch - defines the relationship between
the taxa in terms of descent and ancestryBranch length (scaled trees only) -
represents the number of changes that have occurred in the branch
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Sp e c ie s A
Sp e c ie s E
Sp e c ie s D
Sp e c ie s C
Sp e c ie s BRoot
Branch
CladeNode
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Cladistic Methodologymore
primitivemore
derived
Terminal taxa
X
Y
ZLeopard
Turtle
Salamander
Tuna
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Outgroup Comparison
If the taxon that is not a member of the group of organisms being classified has a character state that is the same as some of the organisms in the group then the character can be considered plesiomorphic
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P P P
P P
P
A
A
A
A
A A
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Characters
TAXON
Moss
Fern
Pine
Daisy
VASCULAR TISSUES SEEDS FLOWERS
P
A
A
A A A
A
P P
P
P
P
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Mos
s
(a) All of the plant groups shown here except mosseshave vascular
Pine Dai
sy
Fern
Node1
Common plantancestor
Common ancestorwith vascular tissues
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Mos
s
Pine Dai
sy
Fern
Node1
Common plantancestor
Common ancestorwith vascular tissues
Node2
(b) Seeds are a shared character for all plant groupsshown here except mosses and ferns.
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Mos
s
Pine Dai
sy
Fern
Node1
Common plantancestor
Common ancestorwith vascular tissues
Node2
Node3
Commonseed-producingancestor
(c) Of the plant groups shown here, only the daisyproduces flowers.
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Cladogram
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Phyletic Group of TaxaMONOPHYLETIC GROUPContains an ancestor and all of its descendants - defined by > 1 shared, derived traits.
POLYPHYLETIC GROUPDoes not include common ancestor group. Common ancestor is placed elsewhere
PARAPHYLETIC GROUPIncludes common ancestor but not all of its descendants. Define by what it lacks.
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WHY DO CLASSIFICATION SCHEMES CHANGE?New Data
Rise of new technologies give new sources of character information
New taxaAs previously unknown species are
discovered, classifications will also need to be revised to reflect their placement
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