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Inferring phylogenies : closely related species should have traits in common

Tracing evolutionary history. Inferring phylogenies : closely related species should have traits in common – inherited from their common ancestor ( homology ) – informative traits are shared derived traits ( homologies that are not the ancestral state)

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Inferring phylogenies : closely related species should have traits in common

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  1. Tracing evolutionary history • Inferring phylogenies: • closely related species should have traits in common • – inherited from their common ancestor (homology) • – informative traits are shared derived traits • (homologies that are not the ancestral state) • identifying shared derived traits requires determining: • – homologies • – ancestralvs. derived states (direction of change)

  2. outgroup – provides information about ancestral state – roots the tree Which traits are ancestral? Which traits are derived?

  3. 3 possible trees – what changes are implied? – which traits are informative? – which tree is best? LH parsimony – fewest changes SM E SM SM E LH LH SM SM E

  4. Use parsimony to build a phylogeny: outgroup? homologies? ancestral vs. derived states? shared derived traits? eggshells four limbs backbone

  5. Tracing evolutionary history • Inferring phylogenies: • closely related species should have traits in common • – inherited from their common ancestor (homology) • – informative traits are shared derived traits • (homologies that are not the ancestral state) • complications arise when traits are shared for other reasons • – convergent evolution • – reversal to the ancestral state

  6. convergence – trait adapted to similar function but with a different origin

  7. Shared traits 1) Homology – inherited from common ancestor

  8. Shared traits 1) Homology – inherited from common ancestor 2) Convergent evolution – similar adaptations

  9. long head? • hair? • smile? • ears? • nose? LH LH LH

  10. long head? • hair? • smile? • ears? • nose? H SM N LH H – shared derived trait H – convergence SM E N H SM N H LH LH H H N SM E SM E N

  11. Same pattern can reflect different evolutionary histories convergent evolution of hair reversal to hairless H – convergence H – reversal OR H LH LH H H N N SM SM E E H

  12. 0 0 1 1 2 2 3 3 4 4 1 A . . . . 2 C G G . . 3 G . . . . 4 C . . . . 5 G . A T T 6 G . . . . 7 T . . C C 8 C . . . . 9 A . . . . 10 T . . A . 11 T . . . . 12 A . . . . DNA base A(5) A(10) sp 0 sp 1 sp 2 sp 3 sp 4 G(2) T(5) C(7) T(12) 1 A . . . . 2 C G G . . 3 G . . . . 4 C . . . . 5 G . T T T 6 G . . . . 7 T . . C C 8 C . . . . 9 A . . . . 10 T . . A . 11 T . . . . 12 A . . . . 12 A T T T T T(5) G(5) sp 0 sp 1 sp 2 sp 3 sp 4 G(2) T(5) C(7) T(5) Phylogenetic analysis of molecular data 12 A T T T T

  13. What are phylogenies good for? • Tracing evolutionary relationships • e.g.: disease transmission (problem set 4) • coevolution (in text) • tree of life • classification • adaptive radiation

  14. Evolutionary relationships – the tree of life

  15. Evolutionary relationships – classification Should birds be distinct from reptiles?

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