What is a synapomorphy?

1
What is a synapomorphy?
2
Terms
systematics taxonomy, phylogenetics phylogeny/ph
ylogenetic tree cladogram tips, branches,
nodes homology apomorphy synapomorhy autapomorphy
plesiomorphy symplesiomorphy homoplasy convergence
reversal of trait
monophyletic paraphyletic polyphyletic tree
polarity outgroup ancestral group sister
group character congruence topological
congruence maximum parsimony
People
Willi Hennig
3
Principles of Phylogenetics Tree Thinking
4
PHYLOGENETIC INFERENCE

• Seeks to recover the historical genetic patterns
• of relationships among organisms

5
PHYLOGENETIC INFERENCE
Principles

• Assumes similar features are homologous until
• shown otherwise

6
HOMOLOGY
correspondence (morphological, molecular,
behavioral) inherited through common ancestry
7
Structural homologies
FH Fig 2.1
8
PHYLOGENETIC INFERENCE
Principles

• Assumes similar features are homologous until
• shown otherwise

Willi Hennig (1950s-1960s)
9
(No Transcript)
10
autapomorphy
uniquely
character
derived
H. sapiens
Australopithecus
11
(No Transcript)
12
(No Transcript)
13
PHYLOGENETIC INFERENCE
Principles

• Assumes similar features are homologous until
• shown otherwise

• Uses shared derived features, not shared
  ancestral
• ones (Hennig formalized this)

• Treats shared derived features (character states)
  as
• markers of historical relatedness

14
PHYLOGENETIC INFERENCE
Principles

• Assumes similar features are homologous until
• shown otherwise

• Uses shared derived features, not shared
  ancestral
• ones (Hennig formalized this)

• Treats shared derived features (character states)
  as
• markers of historical relatedness

• Same basic logic used for comparative
• morphology or DNA

15
Tree-speak
tip
tip
tip
tip
branch
branch
node
16
A simple example..
TANAGER internal skeleton wings 2
legs feathers warm-blooded
TREE FROG internal skeleton no wings 4 legs no
hair or feathers cold-blooded
BUMBLE BEE external skeleton wings 6
legs hair cold-blooded
OPOSSUM Internal skeleton no wings 4
legs hair warm-blooded
17
First taking one character at a time.
Character State
Character State
(1)
(0)
Skeleton
18
(No Transcript)
19
Wings
But.
20
so
21
No
Yes, but convergent
Wings
22
But.
23
so
24
4
6
Legs
really.
25
(actually bumble bees can be endothermic
temporarily)
26
Hair
Just skin
Feathers
Body covering
But.
27
Is hair of opossum and bee really homologous?
Hair
We can test whether these groups share common
ancestry using other characters.
28
Character state trees
No
Yes, but convergent
Wings
29
How can we combine the information from
different characters to infer an overall
phylogeny?
30
How can we combine the information from
different characters to infer an overall
phylogeny?
If for only a few characters with no conflict,
you can do this in your head, but
Quantitative methods are now implemented by
computer to do this!
31
First, make up a character x taxon matrix,
converting ancestral states to 0s and derived
to 1s or 2s
Legs
Skeleton
Wings
Metabolism
Covering
Bumble bee
0
1
1
0
2
Tree frog
1
0
0
0
0
Tanager
1
2
0
1
1
Opossum
1
0
0
1
2
32
How do we know which state of a character is the
ancestral one and which is derived?
--Fossils may help show earlier appearance!
--Outgroup Analysis States found within a group
and also in related groups (outgroups) are more
likely to be ancestral than those found only
within the group
33
Poikilothermy is likely to be ancestral in
frog/bird/mammal group
poikilothermic
34
Legs
Skeleton
Wings
Metabolism
Covering
Bumble bee
0
1
1
0
2
Tree frog
1
0
0
0
0
Tanager
1
2
0
1
1
Opossum
1
0
0
1
2
35
These are then optimized onto possible
phylogenetic trees, and the tree that requires
the fewest total changes of character state is
chosen as the most likely (basic parsimony
analysis)
(It is also possible to make decisions among
trees based upon the likelihood of alternative
changes, rather than simply the evolutionarily
shortest tree (well see this with molecular
data)
36
Skel
Wing
Leg
Metab
Cov
Bumble bee
0
1
2
1
0
Tree frog
1
0
0
0
0
1
Tanager
1
2
0
1
Opossum
1
0
2
0
1
37
How do we resolve differences in relationships
implied by different characters (character state
conflict)?
38
(No Transcript)
39
Using only the shared derived states.!
How many steps or evolutionary changes result
from mapping the different character states onto
these two other tree topologies? Using the
principle of maximum parsimony, which tree would
be selected as the more likely ?
2
2
2
1
1
1
1
8 steps
steps
steps
Cover
Skel
Wing
Leg
Metab
Bumble bee
0
1
1
0
2
Tree frog
1
0
0
0
0
1
Tanager
1
2
0
1
Opossum
1
0
0
1
2
(See next pg.)