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Cladograms and Phylogenetic Trees

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  1. Cladograms and Phylogenetic Trees Ch 25

  2. Overview: Investigating the Tree of Life Phylogeny is the evolutionary history of a species or group of related species Biologists draw on the fossil record, which provides information about ancient organisms

  3. Overview: Investigating the Tree of Life Systematics is an analytical approach to understanding the diversity and relationships of organisms, both present-day and extinct Systematists use morphological, biochemical, and molecular comparisons to infer evolutionary relationships

  4. Concept 25.1: Phylogenies are based on common ancestries inferred from fossil, morphological, and molecular evidence To infer phylogenies, systematists gather information about morphologies, development, and biochemistry of living organisms They also examine fossils to help establish relationships between living organisms

  5. The Fossil Record Sedimentary rocks are the richest source of fossils Sedimentary rocks are deposited into layers called strata The fossil record is based on the sequence in which fossils have accumulated in such strata Fossils reveal ancestral characteristics that may have been lost over time

  6. The Fossil Record Though sedimentary fossils are the most common, paleontologists study a wide variety of fossils

  7. Morphological and Molecular Homologies In addition to fossils, phylogenetic history can be inferred from morphological and molecular similarities in living organisms Organisms with very similar morphologies or similar DNA sequences are likely to be more closely related than organisms with vastly different structures or sequences

  8. Sorting Homology from Analogy In constructing a phylogeny, systematists need to distinguish whether a similarity is the result of homology or analogy Homology is similarity due to shared ancestry Analogy is similarity due to convergent evolution

  9. Sorting Homology from Analogy Convergent evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages Analogous structures or molecular sequences that evolved independently are also called homoplasies

  10. Concept 25.2: Phylogeneticsystematics connects classification with evolutionary history Taxonomy is the ordered division of organisms into categories based on characteristics used to assess similarities and differences In 1748, Carolus Linnaeus published a system of taxonomy based on resemblances. Two key features of his system remain useful today: two-part names for species and hierarchical classification

  11. Binomial Nomenclature The two-part scientific name of a species is called a binomial The first part of the name is the genus The second part, called the specific epithet, is unique for each species within the genus The first letter of the genus is capitalized, and the entire species name is latinized Both parts together name the species (not the specific epithet alone)

  12. Hierarchical Classification Panthera pardus Species Linnaeus introduced a system for grouping species in increasingly broad categories Panthera Genus Felidae Family Carnivora Order Mammalia Class Chordata Phylum Animalia Kingdom Eukarya Domain

  13. Linking Classification and Phylogeny Systematists depict evolutionary relationships in branching phylogenetic trees Panthera pardus (leopard) Mephitis mephitis (striped skunk) Lutra lutra (European otter) Canis familiaris (domestic dog) Canis lupus (wolf) Species Genus Panthera Mephitis Lutra Canis Family Felidae Mustelidae Canidae Carnivora Order

  14. Linking Classification and Phylogeny • Each branch pointrepresents the divergence of two species • “Deeper” branch points represent progressively greater amounts of divergence Leopard Domestic cat Common ancestor Wolf Leopard Domestic cat Common ancestor

  15. Concept 25.3: Phylogeneticsystematics informs the construction of phylogenetic trees based on shared characteristics A cladogram depicts patterns of shared characteristics among taxa A clade is a group of species that includes an ancestral species and all its descendants Cladistics studies resemblances among clades Clades can be nested in larger clades, but not all groupings or organisms qualify as clades

  16. Monophyletic A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants

  17. Paraphyletic A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants

  18. Polyphyletic A polyphyletic grouping consists of various species that lack a common ancestor

  19. Shared Primitive and Shared Derived Characteristics • In cladistic analysis, clades are defined by their evolutionary novelties • A shared primitive character is a character that is shared beyond the taxon we are trying to define • A shared derived character is an evolutionary novelty unique to a particular clade

  20. Outgroups An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared primitive characteristics Outgroup comparison assumes that homologies shared by the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor It enables us to focus on characters derived at various branch points in the evolution of a clade

  21. LE 25-11 TAXA Lancelet (outgroup) Salamander Lamprey Leopard Turtle Tuna Hair Amniotic (shelled) egg CHARACTERS Four walking legs Hinged jaws Vertebral column (backbone) Character table Leopard Turtle Hair Salamander Amniotic egg Tuna Four walking legs Lamprey Hinged jaws Lancelet (outgroup) Vertebral column Cladogram

  22. Practice Use the four cladograms below to answer the following questions: (5) a. Which cladograms have identical topologies (show the same pattern of relationships)? b. On tree 1, circle two different monophyletic groups. c. On tree 2, can you circle those same monophyletic groups. If so, do it! d. On tree 3 circle a paraphyletic group. E. On tree 4, which organisms are more closely related B and C or C and D. How can you tell?

  23. More Practice Answer the questions associated with the following tree: a. Circle the monophyletic group that includes Mimes & Carnies. b. Which group(s) are most closely related to Carnies? c. Are Clowns, Jugglers & Comedians a monophyletic group? If not, who else would need to be included? d. Who is more closely related to Jugglers: Mimes or Clowns, or are they equally related? e. What type of trait is “uses face paint” (e.g. shared ancestral, derived, etc.)?