Phylogeny and Systematics

1
Chapter 25

• Phylogeny and Systematics

2
History of Life (See Table 26.1)
Eras
Boundaries between units in the Geologic Time
Scale are marked by dramatic biotic change
4500
Origin of Earth
3
5 Kingdom classification system in use through
the late 1900s
4
5 Kingdom classification system in use through
the late 1900s gave way to Woeses 3 Domains
5
5 Kingdom classification system in use through
the late 1900s gave way to Woeses 3 Domainsand
multiple Kingdoms
6
Fig. 25.8
Did King Philip Come Over For Gumbo Sunday?
Taxon (taxa) the named taxonomic unit(s) at any
level in this taxonomic hierarchy
Panthera genus pardus specific epithet
that refers to one species in the genus
Panthera
7
Linnaeus convinced us to use a hierarchical
classification system
Darwin provided us with the mechanism by which
evolution results in descent with modification
Taxonomy naming classifying organisms
Systematics naming classifying organisms
according to their evolutionary relationships
Systematic Phylogenetics
Phylogenetics reconstructing the evolutionary
relationships among organisms
8
Macroevolution Phylogeny
hypothesized genealogy traced back to
the last common ancestor (i.e., the most recent)
through hierarchical, dichotomous branching
Phylogenetic tree
Cladistics the principles that guide the
production of phylogenetic trees, a.k.a.,
cladograms
9
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
Node branch point, speciation event
10
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
Lineage or clade an entire branch
11
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
Lineage or clade an entire branch
12
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
Lineage or clade an entire branch
13
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A clade is a monophyletic group, i.e., an
ancestral species and all of its descendents
14
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A clade is a monophyletic group, i.e., an
ancestral species and all of its descendents
15
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A clade is a monophyletic group, i.e., an
ancestral species and all of its descendents
16
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A paraphyletic group consists of an ancestor and
some of its descendents
17
Macroevolution Phylogeny
Phylogenetic tree, phylogeny, or cladogram
A polyphyletic group lacks the common ancestor of
species in the group
18
Macroevolution Phylogeny
Fig. 25.9
Taxonomic groups often reflect true clades
19
Macroevolution Phylogeny
However, tension sometimes exists between
taxonomic tradition and cladistic hypotheses
20
Macroevolution Phylogeny
E.g., If the Class Reptilia is to be
monophyletic, birds must be included!
21
Macroevolution Phylogeny
How are phylogenetic trees constructed?
22
Macroevolution Phylogeny
The fossil record is especially valuable, and the
only option for many extinct taxa
23
Macroevolution Phylogeny
However, we almost never have a continuous record
from one species to the next
24
Macroevolution Phylogeny
Cladistic principles allow us to construct
hypothesized phylogenetic trees
25
Cladistic Analysis
Fossils provide morphological data for extinct
species, whereas comparisons of multiple types of
traits including molecular do so for extant
species
26
Cladistic Analysis
Similar characters (e.g., morphological,
behavioral, molecular, etc. traits or features)
suggest relatedness
Wasps Hymenoptera
27
Cladistic Analysis
But, not all similarity derives from common
ancestry!
Mantisfly Neuroptera
Convergent evolution can produce superficially
similar traits that lack homology with one another
28
Cladistic Analysis
Homologous characters share common ancestry
Lack of similarity among taxa results from
divergence
29
Cladistic Analysis
Analogous characters do not share common ancestry
Similarity among taxa results from convergence
30
Cladistic Analysis
As a general rule, the more homologous
characters shared by two species, the more
closely they are related
Sequences of DNA RNA (nucleotides) and proteins
(amino acids) are used as characters as a
general rule, the more recently two species
shared a common ancestor, the more similar their
sequences
31
Cladistic Analysis
Each nucleotide can be treated as a character
Character changes (mutations) from the ancestral
to the derived state include
Substitutions
AGCTCTAGG
AGCTATAGG
Insertions
AGCTCTAGG
Mutations
AGCTGATCTAGG
Deletions
AGCTCTAGG
AGCTCTAGG
32
Cladistic Analysis
Shared Primitive Characters (ancestral)
Analogies
All similar characters
Homologies
Shared Derived Characters(unique to a clade)
The sequence of branching in a cladogram then
represents the sequence in which evolutionary
novelties (shared derived characters) evolved
33
Cladistic Analysis
Ingroup vs. Outgroup
Ingroup the group whose relationships we are
trying to resolve
Fig. 25.11
34
Cladistic Analysis
Ingroup vs. Outgroup
Outgroup a species (or group) known to have an
older most recent common ancestor with the
ingroup than the ingroups most recent common
ancestor
Fig. 25.11
35
Cladistic Analysis
Ingroup vs. Outgroup
An outgroup helps identify shared ancestral and
shared derived characters (unique to a clade)
Fig. 25.11
36
Cladistic Analysis
Parsimony Occams Razor
The most parsimonious tree is the one that
requires the fewest evolutionary events
(appearance of shared derived characters)
Fig. 25.11
37
Cladistic Analysis
Parsimony Occams Razor
On this most parsimonious cladogram, each key
character originated (evolved) once
Fig. 25.11
38
Cladistic Analysis
An example
Outgroup
Ingroup
See Fig. 25.15 for another example
39
Cladistic Analysis
An example
Outgroup
Ingroup
Create potential topologies for the tree
See Fig. 25.15 for another example
40
Cladistic Analysis
An example
Outgroup
Ingroup
Create potential topologies for the tree
Map the characters onto the trees
See Fig. 25.15 for another example
Choose the most parsimonious tree
41
Macroevolution Phylogeny
Sometimes the most parsimonious arrangement for
one character is not the most accurate overall
Bird-mammal clade
Lizard-bird clade
Fig. 25.16
42
Macroevolution Phylogeny
Dont confuse the age of a clade with the age of
its component species
African Rift Lake Cichlid
Alligator Snapping Turtle
200,000 yr
20,000,000 yr
Based on the cladogram, which species is likely
to be older?
43
Macroevolution Phylogeny
The overall trend is increasing diversity, with
periodic episodes of extinction
Fig. 26.8
44
Macroevolution Phylogeny
Cretaceous mass extinction
Asteroid impacts may have caused mass extinction
events
Permian mass extinction
Extinction of gt90 of species
45
Macroevolution Phylogeny
K-T impact event
46
Macroevolution Phylogeny
Continental drift is responsible for many
cladogenic events biogeograhic distribution
patterns
E.g., Proteaceae a plant family that originated
in Gondwana
47
Continental drift results from plate tectonics
Fig. 26.19
48
Macroevolution Phylogeny
Some biogeographic similarities result from
common ancestry (common descent)
E.g., all bromeliads are found in the New World
Tropics Sub-Tropics
49
Macroevolution Phylogeny
Some biogeographic similarities result from
convergent evolution (convergent adaptive
modification)
E.g., cactus of Americas compared to euphorbs of
Africa
Cactus
Euphorb