What is a synapomorphy?What is a synapomorphy?

TermsTerms

systematics [taxonomy, phylogenetics]phylogeny/phylogenetic treecladogram tips, branches, nodeshomologyapomorphysynapomorhyautapomorphyplesiomorphysymplesiomorphyhomoplasyconvergencereversal of trait

systematics [taxonomy, phylogenetics]phylogeny/phylogenetic treecladogram tips, branches, nodeshomologyapomorphysynapomorhyautapomorphyplesiomorphysymplesiomorphyhomoplasyconvergencereversal of trait

monophyleticparaphyleticpolyphyletictree polarityoutgroupancestral groupsister groupcharacter congruencetopological congruencemaximum parsimony

monophyleticparaphyleticpolyphyletictree polarityoutgroupancestral groupsister groupcharacter congruencetopological congruencemaximum parsimony

PeoplePeopleWilli HennigWilli Hennig

Principles of Phylogenetics:Tree Thinking

Wings

NoYes

PHYLOGENETIC INFERENCE

Seeks to recover the historical genetic patterns of relationships among organisms

PHYLOGENETIC INFERENCE

Principles: Assumes similar features are homologous until shown otherwise

correspondence(morphological,molecular, behavioral)inherited through common ancestry

HOMOLOGY

F&H Fig 2.1

Structural homologies

PHYLOGENETIC INFERENCE

Assumes similar features are homologous until shown otherwise

Willi Hennig(1950s-1960s)

Principles:

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

synapomorphy

shared derived character

HomoAustralopithecus

Large braincases

autapomorphy

uniquely characterderived

H. sapiensAustralopithecus

High forehead

symplesiomorphycharacterancestral shared

HomoAustralopithecus

bipedal

synapomorphy

shared derived character

autapomorphy

uniquely characterderived

symplesiomorphycharacterancestral shared

PHYLOGENETIC INFERENCE

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

Assumes similar features are homologous until shown otherwise

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

Principles:

PHYLOGENETIC INFERENCE

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

Assumes similar features are homologous until shown otherwise

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

Same basic logic used for comparative morphology or DNA

Principles:

Tree-speak

node

tip

branch

branch

tip tiptip

BUMBLE BEEexternal skeletonwings6 legshair“cold-blooded”

TANAGERinternal skeletonwings2 legsfeathers“warm-blooded”

TREE FROGinternal skeletonno wings4 legsno hair or feathers“cold-blooded”

OPOSSUMInternal skeletonno wings4 legshair“warm-blooded”

A simple example…..

First taking one character at a time….

Skeleton

External Internal

Character

Character State Character State

(0) (1)

First taking one character at a time….

Skeleton

External Internal

(0) (1)(1)(1)

Wings

NoYes

But….

bird wings are homologous to front legs of frogs andopossum.and NOT towings of bee

so…

Wings

NoYes, but convergent

But….Legs

2 4 6

so…

bird wings are homologous to front legs of frogs andopossum.so birds have 4 legs!

Legs

4 6

really….

(actually bumble bees can be endothermic temporarily…)

metabolism

Poikilothermic(“cold-blooded”)

Endothermic(“warm-blooded”)

Body covering

Just skin Feathers Hair

But….

Hair

Is hair of opossum and bee really homologous?

We can test whether these groups share common ancestry using other characters….

Skeleton

External Internal

Legs

4 6

Metabolism

Poikilothermic(“cold-blooded”)

Endothermic(“warm-blooded”)

Body covering

Just skin Feathers Hair

Character state trees

Wings

NoYes, but convergent

How can we combine the information from different characters to infer an overall phylogeny?

Skeleton

External Internal

Wings

NoYes, but convergent

Legs

4 6

Metabolism

Poikilothermic(“cold-blooded”)

Endothermic(“warm-blooded”)

Body covering

Just skin Feathers Hair

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!

First, make up a [character x taxon] matrix,

converting ancestral states to 0’s and derived to 1’s or 2’s

Bumble bee

Tree frog

Tanager

Opossum

LegsSkeleton Wings Metabolism Covering

0 1 1 0 2

1 0 0 0 0

1 2 0 1 1

1 0 0 1 2

How do we know which state of a character is the ancestral one and which is derived?

--Fossils may help show earlier appearance!

--Outgroup AnalysisStates found within a group and also in related groups (outgroups) are more likely to be ancestral than those found only within the group

Poikilothermy is likely to be ancestral in frog/bird/mammal group

States found within a group and alsoin related groups (outgroups) are morelikely to be ancestral than those foundonly within the group (ingroup)

outgroup

ingroup

poikilothermicendothermic

Bumble bee

Tree frog

Tanager

Opossum

LegsSkeleton Wings Metabolism Covering

0 1 1 0 2

1 0 0 0 0

1 2 0 1 1

1 0 0 1 2

These are then “optimized” onto possible phylogenetic trees, and the tree that requires the fewest total changes of character stateis chosen as the most likely(basic parsimony analysis)

(It is also possible to make decisions among treesbased upon the likelihood of alternative changes, rather than simply the evolutionarily “shortest” tree (we’ll see this with molecular data)

Using only the shared derived states….!

skeleton

1

wings

1

2

legs

1

metabolism

1

2

covering

21

Bumble bee

Tree frog

Tanager

Opossum

0 1 1 0 2

1 0 0 0 0

1 2 0 11

1 0 0 1 2

Skel Wing Leg Metab Cov

How do we resolve differences in relationships implied by different characters (character state conflict)?

Metabolism

Poikilothermic(“cold-blooded”)

Endothermic(“warm-blooded”)

Body covering

Just skin Feathers Hair

skeleton

1

wings

1

2

legs

1

metabolism

1

2

covering

2

This tree requires 8 steps, including an extra step (homoplasy) due to convergence in covering character

1

CoverBumble bee

Tree frog

Tanager

Opossum

0 1 1 0 2

1 0 0 0 0

1 2 0 1 1

1 0 0 1 2

Skel Wing Leg Metab

Using only the shared derived states….!

11

2

1

1

21

2

8 steps

steps steps

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 ?

(See next pg.)