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Cladistics

Cladistics. Phylogeny. Macroevolution & Phylogeny. – hypothesized genealogy traced back to the last common ancestor ( i.e ., the most recent) through hierarchical, dichotomous branching. Phylogenetic tree.

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Cladistics

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  1. Cladistics Phylogeny

  2. Macroevolution & Phylogeny – hypothesized genealogy traced back to the last common ancestor (i.e., the most recent) through hierarchical, dichotomous branching Phylogenetic tree Cladistics – the principles that guide the production of phylogenetic trees, a.k.a., cladograms

  3. Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram Node – branch point, speciation event

  4. Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram Lineage or clade – an entire branch

  5. Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram A clade is a monophyletic group, i.e., an ancestral species and all of its descendents

  6. Macroevolution & Phylogeny Phylogenetic tree, phylogeny, or cladogram A paraphyletic group consists of an ancestor and some of its descendents

  7. Macroevolution & Phylogeny How are phylogenetic trees constructed?

  8. Macroevolution & Phylogeny The fossil record is especially valuable, and the only option for many extinct taxa

  9. Macroevolution & Phylogeny However, we almost never have a continuous record from one species to the next

  10. Macroevolution & Phylogeny Cladistic principles allow us to construct hypothesized phylogenetic trees

  11. Cladistic Analysis Fossils provide morphological data for extinct species, whereas comparisons of multiple types of traits – including molecular – do so for extant species

  12. Cladistic Analysis Similar characters (e.g., morphological, behavioral, molecular, etc. traits or features) suggest relatedness… Wasps [Hymenoptera]

  13. Cladistic Analysis But, not all similarity derives from common ancestry! Mantisfly [Neuroptera] Convergent evolution can produce superficially similar traits that lack homology with one another

  14. Cladistic Analysis Homologouscharacters share common ancestry Lack of similarity among taxa results from divergence

  15. Cladistic Analysis Analogouscharacters do not share common ancestry Similarity among taxa results from convergence

  16. Cladistic Analysis As a general rule, the more homologous characters shared by two species, the more closely they are related Sequences of DNA & RNA (nucleotides) and proteins (amino acids) are used as characters; as a general rule, the more recently two species shared a common ancestor, the more similar their sequences

  17. Cladistic Analysis Each nucleotide can be treated as a character Character changes (mutations) from the ancestral to the derived state include: Substitutions …AGCTCTAGG… …AGCTATAGG… Insertions …AGCTCTAGG… Mutations …AGCTGATCTAGG… Deletions …AGCTCTAGG… …AGCTCTAGG…

  18. Cladistic Analysis Shared Primitive Characters (ancestral) Analogies All similar characters Homologies Shared Derived Characters(unique to a clade) The sequence of branching in a cladogram then represents the sequence in which evolutionary novelties (shared derived characters) evolved

  19. Cladistic Analysis Ingroup vs. Outgroup Ingroup = the group whose relationships we are trying to resolve Fig. 25.11

  20. Cladistic Analysis Ingroup vs. Outgroup Outgroup = a species (or group) known to have an older most recent common ancestor with the ingroup than the ingroup’s most recent common ancestor Fig. 25.11

  21. Cladistic Analysis Ingroup vs. Outgroup An outgroup helps identify shared ancestral and shared derived characters (unique to a clade) Fig. 25.11

  22. Cladistic Analysis Parsimony & Occam’s Razor The most parsimonious tree is the one that requires the fewest evolutionary events (appearance of shared derived characters) Fig. 25.11

  23. Cladistic Analysis Parsimony & Occam’s Razor On this most parsimonious cladogram, each key character originated (evolved) once Fig. 25.11

  24. Cladistic Analysis An example… Outgroup Ingroup See Fig. 25.15 for another example

  25. Cladistic Analysis An example… Outgroup Ingroup Create potential topologies for the tree See Fig. 25.15 for another example

  26. Cladistic Analysis An example… Outgroup Ingroup Create potential topologies for the tree Map the characters onto the trees See Fig. 25.15 for another example Choose the most parsimonious tree

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