Lecture 3 - Phylogeny and Systematics

• Taxonomy produces a formal system for

  naming and classifying species to illustrate their evolutionary relationship.
• Systematics - broader science of classifying organisms based on similarity, biogeography, etc.
• Classification - denotes the construction of classes.
• Classification - denotes the construction of classes.

  • Grouping of organisms that possess a common feature called an essence used to define the class.
• Systematization places groups of species

  into units of common evolutionary descent.

  • Character variation is used to diagnose systems of common descent.
  • No requirement that an essential character be maintained throughout the system for its recognition as a taxon.
• In classification

  • Taxonomist asks whether a species being classified contains the defining feature of a particular taxonomic class.
• In systematization

  • Taxonomist asks whether the characteristics of a species confirm or reject the hypothesis that it descends from the most recent common ancestor of a particular taxon.
• Carolus Linnaeus designed our hierarchical classification scheme.

  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Names of animal groups at each rank in the hierarchy are called taxa (taxon).
• Binomial nomenclature is the system Linnaeus used for naming species.

  • Genus and species
  • Names are latinized and italicized, only the genus is capatilized.
  • Sitta carolinensis
• A trinomial name includes a subspecies epithet.

  • Otus megalotis megalotis
  • Otus megalotis nigrorum
  • Otus megalotis everetti
• The geographic range of a species is its distribution in space.

  • worldwide species is cosmopolitan.
  • one with a very localized range is called endemic.
• Evolutionary duration of a species is its distribution in time.
• The typological or morphological species concept relies on type specimens that represent the ideal form for the species. When trying to name a specimen, the type specimens were compared.
• The biological species concept emerged during the evolutionary synthesis.

  • “A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature.” Mayr 1982
• The evolutionary species concept states that a single lineage of ancestor- descendant populations that maintains its identity from other such lineages and that has its own evolutionary tendencies and historical fate.
• The phylogenetic species concept is defined as an irreducible (basal) grouping of organisms diagnosably distinct from other such groupings and within which there is a parental pattern of ancestry and descent.
• A major goal of systematics is to infer the evolutionary tree or phylogeny – the evolutionary history of a species or group of related species.
• Shared characters that result from common ancestry are homologous.
• Independent evolution of similar characters that are NOT homologous is called homoplasy.
• A potential misconception in constructing

  a phylogeny is similarity due to convergent evolution, called analogy, rather than shared ancestry.
• Convergent evolution occurs when similar

  environmental pressures and natural

  selection produce similar (analogous)

  adaptations in organisms from different evolutionary lineages.
• A shared primitive character:

  • Is a homologous structure that predates the branching of a particular clade from other members of that clade.
  • Is shared beyond the taxon we are trying to define.
• A shared derived character is an evolutionary novelty unique to a particular clade.
• The form of the character that was present in the common ancestor of the entire group is called ancestral.
• Variant forms of the character arose later and are called derived character states.
• Determining polarity of a character involves determining which state is ancestral.
• Polarity is determined by using outgroup comparison.
• An outgroup is closely related, but not part of the group being examined (the ingroup).
• If a character is found in both the study group and the outgroup, it is considered ancestral for the study group.
• Character groups found in the study groups but not the outgroups are derived.
• Clades are organisms or species that share derived character states and form a subset within a larger group.
• A synapomorphy is a derived character shared by the members of the clade.
• A nested hierarchy is formed by the derived states of all characters in a study group.
• Ancestral character states for a taxon are called plesiomorphic.
• Sharing these ancestral characters is called symplesiomorphy.
• The nested hierarchy of clades can be represented as a cladogram that is based on shared synapomorphies.
• A valid clade is monophyletic.

  • Signifying that it consists of the ancestor species and all its descendants.
• A paraphyletic clade is a grouping that consists of an ancestral species and some, but not all, of the descendants.
• A polyphyletic grouping includes numerous types of organisms that lack a common ancestor.