LECTURE 3B PHYLOGENETIC RECONSTRUCTION Flashcards
a German
entomologist and the proponent of
phylogenetic classification
Willi Hennig (1965)
what helps discover the appropriate degrees of
phylogenetic relationship within a given group of
organisms
phylogenetic systematics
The measurement of the degree of phylogenetic
relationship is
“recency of common ancestry”.
who said The basic rationale of cladistic analysis is “that the more recent the common ancestry of two species, the more characters in common they should have
(Mayr 1969)
“that the more recent
the common ancestry of two species, the more characters in —————–
common they should have
that the more recent the common ancestry of two species, the more characters in common they should have
cladistic analysis
main evidence for phylogenetic relations comes from a
particular kind of characters called
shared derived characters
The main evidence for phylogenetic relations comes from a
particular kind of characters called shared derived characters
and are distributed in
monophyletic groups
who said “The main evidence for phylogenetic relations comes from a particular kind of characters called shared derived characters and are distributed in monophyletic groups”
(Ridley 1996)
The fundamental principle used in most
phylogenetic inference is the
Principle of Parsimony
Principle of phylogenetic reconstruction in which
the phylogeny of a group of species is inferred to
be the branching pattern requiring the smallest
number of evolutionary changes
Principle of Parsimony
is inferred to be the branching pattern requiring the smallest
number of evolutionary changes
Principle of Parsimony
who said “ Principle of phylogenetic reconstruction in which
the phylogeny of a group of species is inferred to
be the branching pattern requiring the smallest
number of evolutionary changes”
(Ridley 1996)
Any hypothesis that requires fewer assumptions is
a more defensible hypothesis
Principle of Parsimony
who said “Any hypothesis that requires fewer assumptions is
a more defensible hypothesis”
(Lipscomb 1998)
The first step in any cladistic analysis is
distinguishing ————from ancestral (plesiomorphic)
characters
derived (apomorphic) characters
The first step in any cladistic analysis is
distinguishing derived (apomorphic)
characters from
ancestral (plesiomorphic) characters
3 methods to distinguish ancestral from derived
- Outgroup comparison
- Embryological criterion
- Fossil record
it involves determining which state is ancestral
polarity
The form of the character that was present in
the common ancestor of the entire group is
called
ancestral
Variant forms of the character arose later and
are called
derived character states
Polarity is determined by using
outgroup comparison
it is closely related, but not part of the
group being examined
outgroup
the group being examined
ingroup
If a character is found in both the study group and
the outgroup, it is considered
ancestral
Character groups found in the study groups but
not the outgroups are
derived
If a 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
plesiomorphic
outside taxon
Outgroup
organisms being classified
ingroup
is a species or
group of species that is closely
related to the ingroup
outgroup
the gorup with
various species being studied
ingroup
is a group that has
diverged before the ingroup
outgroup
who compares each ingroup species with the outgroup to differentiate between shared derived and shared ancestral characteristics
Systematists
what do systematists compare?
ingroup species from outgroup species
Systematists compare each
ingroup species with the
outgroup to differentiate
between?
shared derived and shared ancestral characteristics
Characters shared by
the outgroup and
ingroup are
ancestral characters
they predate the
divergence of both
groups from a
common ancestor
ancestral characters
Two arguments can be made to justify outgroup comparison method
A) based on what we know
about evolutionary process
B) is based on logic
The only way homologous feature could be
present in both an ingroup and an outgroup,
would be for it to have been inherited by
both from an ————————————-
ancestor older than the ancestor of the ingroup
what comparison method is primary one in use today
outgroup comparison method
The outside taxon is called the
outgroup
the organisms being classified are the
ingroup
who proposed the embryological law
Karl Ernst von Baer’s (1792-1876)
embryological law states that;
“The general features of a large group of
animals appear earlier in the embryo than the
special features”.
2 types of features
❖general features
❖“special”
what feature are ancestral characters
general features
what features are evolutionarily derived characters
“special”
This type of investigation is the
—————- ————– of character polarity;
paleontological criterion
can be made by studying fossil
records to determine which character states
are ancestral and which are derived.
Inference
Inference can be made by studying fossil
records to determine which character states
are —— and which are ——–
ancestral;derived
This type of investigation, however, is limited
only to the completeness of fossil records.
paleontological criterion
Taxa that share many derived characters are
grouped more ———- ——— than those that
do not.
closely together
a branching
heirarchical tree called a
cladogram
is constructed following the rule of
parsimony
cladogram
who said “Never assume convergence or parallel
evolution, always assume homology in the
absence of contrary evidence”.
Hennig
when making a ————— it considers the
information provided by each character one at a time.
cladogram
3 steps/methods to make a cladogram
A. Gather and organize data
B. Consider possible cladograms
C. Select best cladogram
3 substeps under step 1 in making a cladogram
- a list of taxa (for example, species) to be organized
- a list of characteristics to be compared
- for each taxon, the value of each of the listed characteristics or character
states
All the data are then organized into a ———-,
which is the base to perform phylogenetic analysis.
taxon-character matrix
what group is primitive?
outgroup
what group is derived?
ingroup
FIRST STEP in cladistic analysis
distinguishing derived from ancestral
All the data collected are then organized into a
“taxon-character matrix”
is the base to perform phylogenetic analysis
“taxon-character matrix”
is considered the primitive characteristics
ancestral
The organism with the most derived characteristics goes to the top of the ———–
last branch
5 detailed step in making a cladogram
- gather and organize data
- All the data are then organized into a “taxon-character matrix”,
which is the base to perform phylogenetic analysis. - Pick the one characteristic common to all organisms. This ancestral is considered the primitive characteristics
- Make a table showing the derived characteristics along the top row and the names of the organisms in the first column
- The cladogram is constructed with the first branch from the bottom belonging to the organism with the fewest derived traits. The organism with the most derived characteristics goes to the top of the last branch
