What is a synapomorphy?
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What is a synapomorphy?. Terms. systematics [taxonomy, phylogenetics] phylogeny/phylogenetic tree cladogram tips, branches, nodes homology apomorphy synapomorhy autapomorphy plesiomorphy symplesiomorphy homoplasy convergence reversal of trait. monophyletic paraphyletic

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Terms

systematics [taxonomy, phylogenetics]

phylogeny/phylogenetic 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


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No

Yes

Wings

Principles of Phylogenetics:

Tree Thinking


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PHYLOGENETIC INFERENCE

  • Seeks to recover the historical genetic patterns

    of relationships among organisms


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PHYLOGENETIC INFERENCE

Principles:

  • Assumes similar features arehomologous until

  • shown otherwise


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HOMOLOGY

correspondence

(morphological,

molecular,

behavioral)

inherited through

common ancestry



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  • Uses shared derived features, not shared ancestral

    ones (Hennig formalized this)

PHYLOGENETIC INFERENCE

Principles:

  • Assumes similar features are homologous until

  • shown otherwise

Willi Hennig

(1950s-1960s)


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synapomorphy

shared

derived

character

Homo

Australopithecus

Large braincases


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High forehead

autapomorphy

uniquely

derived

character

Australopithecus

H. sapiens


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symplesiomorphy

shared

ancestral

character

Australopithecus

Homo

bipedal


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synapomorphy

shared

derived

character

autapomorphy

uniquely

derived

character

symplesiomorphy

shared

ancestral

character


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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


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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


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Tree-speak

tip

tip

tip

tip

branch

branch

node


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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”


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Internal

External

Character

First taking one character at a time….

Character State

Character State

(1)

(0)

Skeleton


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First taking one character at a time….

(1)

(1)

(1)

(0)

Internal

External

Skeleton


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Yes

No

Wings

But….


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bird wings are

homologous

to front legs

of frogs and

opossum.

and NOT to

wings of

bee

so…


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No

Yes, but convergent

Wings


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2

4

6

Legs

But….


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bird wings are

homologous

to front legs

of frogs and

opossum.

so birds

have 4

legs!

so…


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4

6

Legs

really….


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Poikilothermic

(“cold-blooded”)

Endothermic

(“warm-blooded”)

metabolism

(actually bumble bees can be endothermic temporarily…)


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Hair

Just skin

Feathers

Body covering

But….


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Is hair of opossum

and bee really

homologous?

Hair

We can test whether these groups share

common ancestry using other characters….


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External

Internal

Skeleton

4

6

Legs

Poikilothermic

(“cold-blooded”)

Endothermic

(“warm-blooded”)

Just skin

Feathers

Hair

Body covering

Metabolism

Character state trees

Yes, but convergent

No

Wings


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How can we combine the information from different

characters to infer an overall phylogeny?

External

Internal

Yes, but convergent

No

Skeleton

Wings

4

6

Legs

Poikilothermic

(“cold-blooded”)

Endothermic

(“warm-blooded”)

Just skin

Feathers

Hair

Body covering

Metabolism


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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!


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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


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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


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States found within a group and also

in related groups (outgroups) are more

likely to be ancestral than those found

only within the group (ingroup)

endothermic

outgroup

ingroup

Poikilothermy is likely

to be ancestral in

frog/bird/mammal group

poikilothermic


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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


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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 (we’ll see this with molecular data)


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Using only the shared derived states….!

1

2

2

2

1

1

1

1

skeleton

legs

metabolism

covering

wings

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


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Feathers

Just skin

Hair

Body covering

Poikilothermic

(“cold-blooded”)

Endothermic

(“warm-blooded”)

Metabolism

How do we resolve differences in

relationships implied by different

characters (character state conflict)?


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This tree requires 8 steps, including an extra step

(homoplasy) due to convergence in covering character

1

2

2

2

1

1

1

1

skeleton

legs

metabolism

covering

wings


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1

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

Skel

Wing

Leg

Metab

Cover

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.)


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