3. Treats shared derived features (character states) as markers of historical relatedness
Treats shared derived features (character states) as markers of historical relatedness 4. Same basic logic used for comparative morphology or DNA
A simple example….. TANAGER
TREE FROG
internal skeleton wings 2 legs feathers “warm-blooded”
internal skeleton no wings 4 legs no hair or feathers “cold-blooded”
BUMBLE BEE
OPOSSUM
external skeleton wings 6 legs hair “cold-blooded”
Internal skeleton no wings 4 legs hair “warm-blooded”
First taking one character at a time….
Character State
Character State
External (0)
Skeleton
Internal (1)
Character
2
First taking one character at a time….
(1)
(0)
(1)
(1)
Yes
No
Internal
External
Wings
Skeleton
bird wings are homologous to front legs of frogs and opossum. and NOT to wings of bee
Yes, but convergent
But….
No
Wings
so…
2
4
Legs
bird wings are homologous to front legs of frogs and opossum. so birds have 4 legs!
6
But….
so…
3
4
Poikilothermic (“cold-blooded”)
6
metabolism
Legs
really….
Endothermic (“warm-blooded”)
(actually bumble bees can be endothermic temporarily…)
Is hair of opossum and bee really homologous?
Just skin
Hair
Feathers
Hair
Body covering
But….
How can we combine the information from different characters to infer an overall phylogeny?
Character state trees
External
Internal
Yes, but convergent
No
Wings
Skeleton
4
We can test whether these groups share common ancestry using other characters….
External
Internal
Skeleton
6
Endothermic (“warm-blooded”)
Metabolism
No
Wings
4
Legs
Poikilothermic (“cold-blooded”)
Yes, but convergent
6
Legs
Just skin Feathers
Hair
Body covering
Poikilothermic (“cold-blooded”)
Endothermic (“warm-blooded”)
Metabolism
Just skin Feathers
Hair
Body covering
4
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 if there is conflict quantitative methods are now implemented by computer to do this!
How do we know which state of a character is the ancestral one and which is derived?
First, make up a [character x taxon] matrix, converting ancestral states to 0’s and derived to 1’s or 2’s
Skeleton
Wings
Legs 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
States found within the group of interest (ingroup) and also in related groups (outgroups) are more likely to be ancestral than those found only in the ingroup
-- Fossils may help show earlier appearance! -- Outgroup Comparison Considers that states found within the group of interest (ingroup) and also in related groups (outgroups) are more likely to be ancestral than those found only in the ingroup
endothermic poikilothermic outgroup ingroup
Skeleton
Wings
Legs 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
Poikilothermy is likely to be ancestral
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 maximum 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 (we’ll see this with molecular data)
5
Using only the derived states….! How do we resolve differences in relationships implied by different characters (character state conflict)?
1
2 1
1
1 1 skeleton
2
2
Skel Wing Leg Metab Cov Bumble bee 0 1 2 1 0 Tree frog
1
0
0
0
0
Tanager
1
2
0
1
1
Opossum
1
0
0
1
2
legs metabolism
wings
Poikilothermic (“cold-blooded”)
Endothermic (“warm-blooded”)
Just skin
Feathers
Hair
Body covering
Metabolism
covering
Using only the derived states….!
This tree requires 8 steps, including an extra step (homoplasy) due to convergence in covering character
How many steps or evolutionary changes result from mapping the different character states onto these two other tree topologies?
1 2 2
1
1
Using the principle of maximum parsimony, which tree would be selected as the more likely ?
2
1 1
8 steps
1
2
2
Skel Wing Leg Metab Cover Bumble bee 0 1 1 0 2 Tree frog 1 0 0 0 0
monophyletic paraphyletic polyphyletic tree polarity outgroup ancestral group sister group character congruence topological congruence maximum parsimony