Principles of Life, Ch. 14 Reading

14.1 All of Life is Connected through Its Evolutionary History

• Phylogeny: The evolutionary history of a particular group of organisms or their genes.

• Phylogenetic Tree: A graphic representation of the lines of descent among organisms or their genes.

• Phylogenetic trees depict evolutionary relationships among lineages

  • Lineage: A series of populations, species, or genes descended from a single ancestor over evolutionary time.
  • An event that splits a lineage is called a node
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  • A phylogenetic tree may portray the evolutionary history of all life forms.
  • Root: In reference to phylogenetic trees: the base (oldest) part of the tree
  • The order in which nodes are placed along the horizontal (time) axis has meaning, but the vertical distance between the branches does not.
  • Taxon: A biological group (typically a species or clade) that is given a name.
  • Clade: A monophyletic group made up of an ancestor and all of its descendants; Any taxon that consists of all the evolutionary descendants of a common ancestor
  • Homologous Features: A similarity between two or more features that is due to inheritance from a common ancestor; e.g. wings

• Derived traits provide evidence of evolutionary relationships

  • Each character of an organism evolves from one condition (the ancestral trait) to another condition (the derived trait).

  • Ancestral trait: The trait originally present in the ancestor of a given group; may be retained or changed in the descendants of that ancestor.

  • Derived trait: A trait that differs from the ancestral trait.

  • Synapomorphies: A trait that arose in the ancestor of a phylogenetic group and is present (sometimes in modified form) in all of its members, thus helping delimit and identify that group. Also called a shared derived trait.

  • Similar traits in unrelated groups can develop because…

  • Convergent evolution: Independent changes to the same state or trait in two or more groups of organisms.

    • For example, although the forelimb bones of bats and birds are homologous, having been inherited from a common tetrapod ancestor, the wings of bats and birds are not homologous because they evolved independently from the forelimbs of different nonflying ancestors
    • Analogous: similar structures found in two or more groups of organisms, but with separate, independent evolutionary origins.

  • Evolutionary reversal: The reappearance of an ancestral trait in a group that had previously acquired a derived trait.

  • Homoplasies: The presence in multiple groups of a trait that is not inherited from the common ancestor of those groups. Can result from convergent evolution, evolutionary reversal, or parallel evolution.

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14.2 Phylogeny Can Be Reconstructed from Traits of Organisms

• Shared traits reflect common ancestry

  • Ingroup: In a phylogenetic study, the group of organisms of primary interest
  • Outgroup: a group of organisms used as a point of reference for comparison with the groups of primary interest
  • The root of the tree is located between the ingroup and the outgroup
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• Parsimony provides the simplest explanation for phylogenetic data

  • Parsimony Principle: The principle that states that the preferred explanation of observed data is the simplest explanation.
  • the best hypothesis under the parsimony principle is one that requires the fewest homoplasies
  • This application of parsimony is a specific case of a general principle of reasoning called Occam’s razor: the best explanation is the one that best fits the data while making the fewest assumptions.

• Phylogenies are reconstructed from many sources of data

  • Any trait that is genetically determined, and therefore heritable, can be used in a phylogenetic analysis.
  • Morphology: The scientific study of organic form, including both its development and function; the presence, size, shape, and other attributes of body parts
  • Cons… Some taxa exhibit little morphological diversity, despite great species diversity; few morphological traits can be compared across distantly related species (earthworms and humans); some morphological traits are because of environment, not genetics
  • Development
  • Some things have features that are present only in the embryonic stage
  • Paleontology
  • When did lineages diverge
  • Behavior
  • Molecular data (DNA)

• The accuracy of phylogenetic methods can be tested

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14.3 Phylogeny Makes Biology Comparative and Predictive

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• Molecular clock: The approximately constant rate of divergence of macromolecules from one another over evolutionary time; used to date past events in evolutionary history.

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14.4 Phylogeny Is the Basis of Biological Classification

• Binomial nomenclature: Phylogeny Is the Basis of Biological Classification

• Linnaean classification is based on standard taxon ranks

  • Genus: A group of related, similar species recognized by taxonomists with a distinct name used in binomial nomenclature.
  • In the Linnaean system, species and genera are further grouped into a hierarchical system of higher taxonomic categories. The taxon above the genus in the Linnaean system is the family.
  • the suffix “-aceae” is used for plant family names and “-idae” is for animals
  • families are grouped into orders, orders into classes, classes into phyla (singular phylum), and phyla into kingdoms
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  • Monophyletic: Pertaining to a group that consists of an ancestor and all of its descendants.
  • Polyphyletic: Pertaining to a group that consists of multiple distantly related organisms, and does not include the common ancestor of the group.
  • Paraphyletic: Pertaining to a group that consists of an ancestor and some, but not all, of its descendants.

• Several codes of biological nomenclature govern the use of scientific names

  • The rules of biological nomenclature are designed so that there is only one correct scientific name for any single recognized taxon, and (ideally) a given scientific name applies only to a single taxon (that is, each scientific name is unique).

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