Example 1 Example 2 Does it work? Testing ancestral reconstructions in the laboratory

or

or

or

=

ancestor

descendants

?

Down pass

Up pass (if needed)

Example 1

Example 2

Does it work?

Testing ancestral reconstructions in the laboratory

J MR K L N Q O P

A B C D

E F

W

15 16

7 16

9 15 11 21 22 16

19 18

1817

34

wild-type T740 serial lysates2/3 generations per lysate

T7 bacteriophage in presence of N-methyl-N’ -n itro-N-n itroguanidine

Experimental phylogenetics

Comparing actual ancestors with inferred ancestors

Parsimony got it 94% right

Two cases where

parsimony got it wrong

- -- - - - - + -

- - - +

- -

-

- -- - - + + + +

- - + +

- -

-

Bgl II

Mbo I

Catalytic activity

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

50 42 38 30 25 20 15 12 8

Time (millions of years)

Jurassic Park revisited

Recreating ancestral proteins

Taxonomic sampling and missed changes

-

+ +

+

- -

--

-

-

2 changes 1 change no changes

actual reconstructed (without a taxon)

Problem is acute on long branches, especially for molecular data

A

T

T T

A

G

G

GG

A

Molecular trees are often imbalanced

How do characters evolve?

Ordered characterFused, size 1

Touching

Separate

Fused, size 2

Unordered character

Fused, size 1

TouchingSeparate

Fused, size 2

Dollo parsimony“once lost, complex structures are never regained”

1

0

1

0

Standard parsimony Dollo parsimony

commononce only

Wing loss and gain in stick insectsWhiting M. F. et al. Nature 421, 264-267 (2003)

Testing hypotheses

• When did a character evolve?

• Has it evolved more than once?

• Did one character evolve before another?

• Is the evolution of two (or more) characters correlated?

Swordtails and platys

Origin of swords in swordtail fishes:the “pre-existing bias hypothesis”

Idea:

Females evolve a “sensory bias” which causes them to prefer males with exaggerated features. Hence, male morphology is driven by sexual selection.

Testing this idea...

• Female choose males based on sword length. Experiments on X. helleri show females prefer males with longer

swords.

• Females of swordless species (platys) prefer males with swords. Experiments on X. maculatus confirm this.

• Absence of swords must be primitive, so that female's bias for swords predates the evolution of swords.

?

Swords are primitive!

X. couchianusX. gordoniX. meyeriX. xiphidiumX. variatusX. evelynaeX. clemenciaeX. milleriX. maculatusX. andersiX. signumX. helleriX. alvereziX. birchmanniX. pygmaeusX. montezumaeX. nezehualcoyotiX. continensX. corteziX. malincheX. nigrensisX. multilineatusP. compressP. intermediaP. olmecae

Correlated evolution

Have two characters evolved together?

Gregariousness in aposematic butterfly larvae

• Aposematic forms tend to be gregarious. R. A. Fisher suggested warning colouration evolved through kin selection.

• An individual may die during the “lesson” that teaches naïve predator not to eat brightly coloured larvae

• If predator leaves kin alone, inclusive fitness of dead larvae is positive

• Laying eggs in clutches will result in kin groups on same plant

• Prediction: aggregation evolves before colouration

Correlated character change

AB

AB

AB

ab

A

B

AB

AB

Ab

ab

A

B

Does character A always arise with character B?Does character A always precede character B?

Prediction based on kin selection

unpalatable

gregarious

unpalatable

gregarious

Results: gregariousness evolves after unpalatability

unpalatable

gregarious

unpalatable

gregarious

Comparative method

Phylogeny makes cross-species comparisons non independent

Species aren’t independent

A

C

B

D

E F

A B C D E F

A B C D E F

Bird bills vary in size

Lice are a problem for birds

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Independent contrasts

Bird with big bills scratch more

0 0.1 0.2 0.3 0.4 0.5 0.6

Toucanet/Aracari

Woodpecker/Jacamar

Hornbill/Roller

Hummingbird/Turacos

Curlew/Ruff

Oystercatcher/Avocet

Ibis/Falcon

Stork/New Worldvulture

Pelican/penguin

Proportion of time spent grooming

Long

Short

Summary

• Given a phylogeny we can infer ancestral states

• These states can be used to test hypotheses• Comparisons between species are not

independent• The comparative method provides tools to

extract independent comparisons from a phylolgeny