Transcript Taxonomy & Phylogeny

Taxonomy &
Phylogeny
Introduction
Classification
Phylogeny
Cladograms
Quiz
In this tutorial, you will learn:
 The
traditional classification scheme of
Linnaeus.
 Two theories of taxonomy:


Traditional evolutionary taxonomy
Cladistics
 How
to read a cladogram
Credits:
Figures and images by N. Wheat unless otherwise noted.
Image of Linnaeus from Wikipedia
Funded by Title V-STEM grant P031S090007.
Introduction
 The
practice of categorizing organisms
according to similar features goes back to
Aristotle.
 The goal of Taxonomy today is to
produce a formal system for naming and
classifying species to illustrate their
evolutionary relationships.
Classification vs. Systematization
 In
classification, the taxonomist asks
whether the species being classified
contains the defining feature of a certain
taxonomic grouping.

Focus is on features.
Classification vs. Systematization
 In
systematization, the taxonomist asks
whether the characteristics of a species
support the hypothesis that it descends
from the most recent common ancestor
of the taxonomic group.

Focus is on evolutionary origin of those
features.
Linnaeus and Classification
 In
the 18th century, Carolus Linnaeus
designed the hierarchical classification
system still in use today.
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Kingdom
Phylum
Class
Order
Family
Genus
Species
Taxa
 Taxa
(singular = taxon) are the major
groups of organisms.

Each rank can be subdivided into
additional levels of taxa.
 Superclass,
suborder, etc.
Binomial Nomenclature
 Binomial
nomenclature is the system
Linnaeus developed for naming species.
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The two-part scientific name includes the
genus and species
Names are latinized and italicized, only the
genus is capatilized.
Sitta carolinensis
Phylogeny
 The
goal of systematics is to determine
the phylogeny – the evolutionary history –
of a species or group of related species.
Phylogeny
 Phylogenies
are inferred by identifying
organismal features, characters, that vary
among species.
 These characters can be:
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Morphological
Chromosomal
Molecular
Behavioral or ecological
Homology
 Homologous
characters are shared
characters that result from common
ancestry.
Homoplasy
 Homoplasies
are shared characters that
are not a result of common ancestry, but
of independent evolution of similar
characters (they are not homologous).
 Can
result from convergent evolution.
Convergent Evolution
 Convergent
evolution occurs when
natural selection, working under similar
environmental pressures, produces similar
(analogous) adaptations in organisms
from different evolutionary lineages.
Phylogeny
 When
trying to determine evolutionary
relationships (inferring a phylogeny), we
only want to consider homologous
characters.

Homoplasies can create errors.
Shared Primitive and Shared
Derived Characteristics
 Focusing
on homologous structures, we
need to determine when that character
arose.
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
Newer characters tell us more!
Primitive (older) vs. derived (newer)
characters
Shared Primitive and Shared
Derived Characteristics
A
shared primitive character is a
homologous structure that is older than
the branching of a particular clade from
other members of that clade.
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
It is shared by more than just the taxon we
are trying to define.
Example – mammals all have a backbone,
but so do other vertebrates.
Shared Primitive and Shared
Derived Characteristics
A
shared derived character is a new
evolutionary feature, unique to a
particular group.

Example - all mammals have hair, and no
other animals have hair.
 These
are the features that are most
useful for determining evolutionary
relationships!
Ancestral Character States
 The
ancestral character state is the form
of the character that was present in the
common ancestor of the group.
 Variations of the character that arose
later are called derived character states.
Polarity
 Polarity
(which version of the trait is
ancestral) is determined by using
outgroup comparison.

An outgroup is closely related, but not part
of the group being examined (the ingroup).
Polarity
 An
ancestral character is one that is
found in both the study group and the
outgroup.
 Derived character groups are those found
in the study groups but not the outgroups.
Clades
 Clades
are groups that share derived
characters and form a subset within a
larger group.
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A clade is a unit of common evolutionary
descent.
Synapomorphy
A
synapomorphy is a derived character
that is shared by all the members of the
clade.

Using synapomorphies to define clades will
result in a nested hierarchy of clades.
Symplesiomorphy
 Ancestral
character states for a taxon are
called plesiomorphic.
 Symplesiomorphies are shared ancestral
characters.

Symplesiomorphies do not provide useful
information for forming a nested series of
clades.
Cladogram
 The
nested
hierarchy of
clades can be
shown as a
cladogram that is
based on
synapomorphies.
Monophyletic
A
valid clade is
monophyletic, it
consists of the
ancestor species
and all its
descendants.
Paraphyletic
A
paraphyletic
clade consists of
an ancestral
species and some,
but not all, of the
descendants.
Polyphyletic
A
polyphyletic
clade includes
many species
that lack a
common
ancestor.
Cladistics
 Cladistics,
also called phylogenetic
systematics, is a taxonomic theory that is
based on cladograms.
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All taxa must be monophyletic!
Evolutionary Taxonomy
 Traditional
Evolutionary
taxonomy is based
on common descent
and the amount of
evolutionary change
to rank higher taxa.
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Sometimes this type
of classification
includes paraphyletic
groupings.
Cladistics
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Since all groupings
must be monophyletic
in cladistics, the
paraphyletic
arrangement of ape
families doesn’t work.
Humans, chimpanzees,
gorillas, and
orangutans are now all
included together in
one monophyletic
family - Hominidae.
Sister Groups
A
sister group is a pair of taxa that are
most closely related to each other.
 Humans are most closely related to
chimpanzees, so humans & chimpanzees
form a sister group.
 Gorillas form a sister group to the clade
containing humans and chimpanzees.
Cladistics vs. Evolutionary
Taxonomy
 The
important difference between these
two theories of taxonomy is that
traditional evolutionary taxonomy
sometimes accepts paraphyletic clades,
while cladistics does not.
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Both accept monophyletic clades.
Both reject polyphyletic clades.
Question 1
Who developed the classification
system including the binomial
scientific name in use today?
 Darwin
 Mendel
 Linnaeus
 Aristotle
Question 1
Sorry!
 That
is incorrect.
 Try again!
Question 1
Congratulations!
 You
are correct!
Question 2
Which of the following are
considered to be taxa?
 Phylum
 Class
 Family
 Species
 All
of the above
Question 2
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 That
is incorrect.
 Try again!
Question 2
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 You
are correct!
Question 3
Which example of binomial
nomenclature is formatted
correctly?
 Homo
sapiens
 homo sapiens
 Homo Sapiens
 Homo Sapiens
 It doesn’t matter, they are all
correct
Question 3
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 That
is incorrect.
 Try again!
Question 3
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 You
are correct!
Question 4
Which of these terms is associated
with characters that share common
ancestry.
 Homology
 Convergent
evolution
 Homoplasy
 Analogy
 All
of the above
Question 4
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 That
is incorrect.
 Try again!
Question 4
Congratulations!
 You
are correct!
Question 5
When defining a clade, what type
of characters should we use?
 Homoplasies
 Shared
primitive characters =
symplesiomorphies
 Shared derived characters =
synapomorphies
 All of the above
Question 5
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 That
is incorrect.
 Try again!
Question 5
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 You
are correct!
Question 6
The branching diagram that
illustrates the nesting hierarchy of
clades is called a
 Family
tree
 Cladogram
 Phylogenetic diagram
 Taxonomic web
Question 6
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 That
is incorrect.
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Question 6
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 You
are correct!
Question 7
A monophyletic clade is one
that contains
 An
ancestor and all of its
descendants.
 An ancestor and some of its
descendants.
 Several species that lack a
common ancestor.
 One species.
Question 7
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 That
is incorrect.
 Try again!
Question 7
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 You
are correct!
Question 8
A polyphyletic clade is one
that contains
 An
ancestor and all of its
descendants.
 An ancestor and some of its
descendants.
 Several species that lack a
common ancestor.
 One species.
Question 8
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 That
is incorrect.
 Try again!
Question 8
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 You
are correct!
Question 9
A paraphyletic clade is one
that contains
 An
ancestor and all of its
descendants.
 An ancestor and some of its
descendants.
 Several species that lack a
common ancestor.
 One species.
Question 9
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 That
is incorrect.
 Try again!
Question 9
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 You
are correct!
Question 10
This cladogram illustrates a
________________ clade.
 Monophyletic
 Paraphyletic
 Polyphyletic
 None
of the above
Question 10
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 That
is incorrect.
 Try again!
Question 10
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 You
are correct!
Question 11
Which of the following statements about the
difference between cladistics and traditional
evolutionary taxonomy is false?
 Both
accept monophyletic clades
 Both accept paraphyletic clades
 Cladistics rejects paraphyletic clades,
while evolutionary taxonomy sometimes
accepts them.
 Both reject polyphyletic clades.
Question 11
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 That
is incorrect.
 Try again!
Question 11
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 You
are correct!
Question 12
Which of the following cladograms
incorrectly illustrates sister groups?
Question 12
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 That
is incorrect.
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Question 12
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 You
are correct!