Transcript Evolution- Phylogeny PPT Lecture

Phylogeny and Systematics
(Part 6)
Chapter 25: Phylogeny and Systematics
(Making “Trees of Life”)
AP Biology
Ms. Gaynor
Macroevolution
• studies focus on change that occurs at or
above the level of species
▫ The origin of taxonomic groups higher than
species level
How does this occur?
• Evolution of new traits (novelties)
• mass extinctions
• Open adaptive zones (divergent evolution)
• Currently, scientists use
▫ Morphological, biochemical, and molecular
comparisons to infer evolutionary relationships
 Obtained through fossil studies, DNA technology
and current organisms
Phylogeny
What is phylogeny?
• The evolutionary history of a group
• Systematics attempts to reconstruct
phylogeny, by analyzing evolutionary
relatedness.
▫ Use morphological and biochemical similarities
• Molecular systematics uses DNA, RNA and
proteins to infer evolutionary relatedness.
• Different tools are used to reconstruct
phylogenies called phylogentic trees.
Molecular
systematics
Systematics
• Uses evidence from fossil record and
existing organisms to reconstruct
phylogeny
• Uses branching taxonomic categories so
that they reflect phylogeny
• Binomial nomenclature Genus species
keeps identity of organism universal
▫ Other taxa used to classify
 Domain, Kingdom, Phylum, Class, Order, Family
Genus, species
Taxonomy
Linnaeus ordered
division of
organisms into
categories based
on a set of
characteristics
used to assess
similarities and
differences
Linking Classification and Phylogeny
Species
Panthera
Figure 25.9
Order
Family
Panthera
Mephitis
Canis
Canis
Lutra lutra
pardus
mephitis
familiaris
lupus
(European
(leopard) (striped skunk)
(domestic dog) (wolf)
otter)
Genus
• Systematists depict evolutionary relationships
In branching phylogenetic trees
Felidae
Mephitis
Lutra
Mustelidae
Carnivora
Canis
Canidae
• Each branch point
▫ Represents the divergence of two species
Leopard
Domestic cat
Common ancestor
• “Deeper” branch points
▫ Represent progressively greater amounts of
divergence
Wolf
Leopard
Common ancestor
Domestic cat
• A cladogram
▫ a depiction of patterns of shared
characteristics among taxa
• A clade within a cladogram
▫ a group of species that includes an
ancestral species and all its
descendants
• Cladistics
▫ the study of resemblances among
clades
Cladistics
• Cladogram is a tree with
two way branch points
• Each branch point
represents divergence
from common ancestor
• Each branch is called a
clade
• Clades
▫ Can be nested within larger
clades, but not all
groupings or organisms
qualify as clades
• 3 types of groupings
▫ Monophyletic
▫ Polyphyletic
▫ Paraphyletic
Different Types of Clades
• Monophyletic = single ancestor gave rise to all
species in the taxon; ONLY valid clade
• Polyphyletic = includes numerous types of
organisms that lack a common ancestor; not a
valid clade
• Paraphyletic = a grouping that consists of an
ancestral species and some, but not all, of the
descendants; not a valid clade
• Creating the ideal monophyletic taxa is not
always easy.
Clades
Grouping 1
Monophyletic
Grouping 2
Paraphyletic
Grouping 3
Polyphyletic
Let’s practice…
Making “Trees”: Morphological &
molecular homologies
• similarities based on shared ancestries
▫ bone structure
▫ DNA sequences
• beware of analogous structures
 SAME function DIFFERENT development
(opposite of homologous structures)
 This is a result of convergent evolution
Not all Similarities Represent
Common Ancestry
• Homologous structures indicate shared
common ancestry
▫ Homologous structures are therefore
evidence of divergent evolution
• Analogous structures are similar in
function but not in evolutionary history
▫ Analogous structures are evidence of
convergent evolution
• It is not always easy to sort homologous
from analogous structures
Analogous structures or molecular
sequences that evolved independently
Are also called homoplasies
How would you compare the fins in
these 2 organisms?
• RECALL…
• Convergent evolution occurs when similar
environmental pressures and natural selection
▫ Produce similar (analogous) adaptations in
organisms from different evolutionary lineages
Marsupial
Eutherian
(placental)
How do we differentiate between
homologous and analogous
structures?
• Compare embryonic development of the
structures in question
• Compare macromolecules along with
anatomical features called comparative
molecular biochemistry.
Making Evolutionary Life Trees:
Illustrating Phylogeny
• 1. Cladistics = NOT TIME RELATED
▫ sorts homologous from analogous
structures
▫ sorts primitive and shared derived
characteristics
▫ Makes cladograms
• 2. Phenetics = TIME RELATED
▫ compares many biochemical
similarities/ differences (NOT
overall phenotype) to construct
phylogeny
▫ Does not sort homologous from
analogous structures.
• Creates phylogenetic trees or
phylograms
The Universal Tree of Life
• The tree of life is divided into three great clades called
domains:
▫ Bacteria, Archaea, and Eukarya
Billion years ago
Bacteria
Eukarya Archaea
0
4
Symbiosis of
chloroplast
ancestor with
ancestor of green
plants
1
3
Symbiosis of
mitochondrial
ancestor with
ancestor of
eukaryotes
2
Possible fusion
of bacterium
and archaean,
yielding
ancestor of
eukaryotic cells
1
Last common
ancestor of all
living things
4
2
3
2
3
1
Origin of life
Figure 25.18
4
• A shared primitive character
▫ a homologous structure that is
shared by all groups we are
trying to define
• A shared derived character
▫ A new evolutionary trait unique
to a particular clade(s)
Shared Derives Characteristics
• Need to differentiate between shared
primitive characters and shared derived
characters
Analogies
All similar
characters
Primitive
(ancestral)
Homologies
Derived
(unique to
a clade)
Outgroups vs. Ingroups
• Outgroup
▫ The species or group of species that is
closely related to the ingroup
▫ Distinguishes between shared primitive
and shared derived characteristics
▫ Closely related to ingroup
• Ingroup
▫ the various species we are studying
A Cladogram
What is the shared primitive characteristic? Notochord
Phylograms
• In a phylogram
▫ The length of a branch in a
cladogram reflects the
number of genetic changes
that have taken place in a
particular DNA or RNA
sequence in that lineage
▫ Involves timing
cladograms do NOT!
65.5
Cenozoic
251
Mesozoic
Millions of
years ago
542
Paleozoic
Proterozoic
http://www.hippoc
ampus.org/Hippo
Campus/Biology;js
essionid=876F059
F821B397C549B7
4C3A53EB28F
Phylogenetic trees are hypotheses
Which is the most parsimonious tree?
Parsimony does not always work, nature
does not always take the simplest
course