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

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Presentation on theme: "Example 1 Example 2 Does it work? Testing ancestral reconstructions in the laboratory."— Presentation transcript:


2 Example 1 Example 2

3 Does it work? Testing ancestral reconstructions in the laboratory


5 Comparing actual ancestors with inferred ancestors Parsimony got it 94% right

6 Two cases where parsimony got it wrong

7 Jurassic Park revisited Recreating ancestral proteins

8 Taxonomic sampling and missed changes - + + + - - - - - - 2 changes1 changeno changes actual reconstructed(without a taxon)

9 Problem is acute on long branches, especially for molecular data A T TT A G G GG A

10 Molecular trees are often imbalanced

11 How do characters evolve?

12 Ordered character Fused, size 1 Touching Separate Fused, size 2

13 Unordered character Fused, size 1 Touching Separate Fused, size 2

14 Dollo parsimony once lost, complex structures are never regained 1 0 1 0 Standard parsimony Dollo parsimony common once only

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


17 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?

18 Swordtails and platys

19 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.

20 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. ?

21 Swords are primitive!

22 Correlated evolution Have two characters evolved together?

23 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

24 Correlated character change AB ab A B AB Ab ab A B Does character A always arise with character B? Does character A always precede character B?

25 Prediction based on kin selection unpalatable gregarious unpalatable gregarious

26 Results: gregariousness evolves after unpalatability unpalatable gregarious unpalatable gregarious

27 Comparative method Phylogeny makes cross-species comparisons non independent

28 Species arent independent A C B D E F ABCDEF ABCDEF

29 Bird bills vary in size

30 Lice are a problem for birds

31 Independent contrasts

32 Bird with big bills scratch more

33 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

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