Systematics

Systematics and Phylogeny

• Systematics: The science of naming and classifying organisms and their evolutionary relationships.

• Phylogenetics: Reconstructing phylogeny using diagrams known as tree of life.

Three Domains of Life

• Bacteria: Single-cell prokaryotes.

• Archaea: Single-cell prokaryotes that are ancient.

• Eukarya: Organisms made of eukaryotic cells.

  • Sister Groups: Archaea and Eukarya are sister groups.

  • Animals: Belong to the domain Eukarya (eukaryotic cells).

    • Animals do not photosynthesize.

    • They ingest and digest food within their bodies.

Linnaean System of Classification

• Hierarchy (from most inclusive to least inclusive):

  • Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species.

• Naming Conventions:

  • Uses Greek and Latin, which do not change, making it universal and preventing confusion.

  • Binomial Nomenclature: Two-word naming system.

    • First Word (Genus): Capitalized (e.g., Homo).

    • Second Word (Species Epithet): Not capitalized (e.g., sapiens).

    • Entire name should be italicized or underlined when written by hand.

  • Example: Homo sapiens (humans), Oryctolagus cuniculus (rabbits).

General Rules for Species Names

• Species epithets may be reused with a different genus name, but the combination is unique and refers to one specific species.

• Taxa Names:

  • All taxon names (genus, family) should be unique.

  • Genus names by themselves should be italicized or underlined.

  • Names of higher taxa are capitalized, but never italicized or underlined (e.g., Domain Eukarya, Order Stromatoliferes).

Understanding Phylogeny

• Phylogeny: A diagram that shows relationships among species.

• Extant vs. Extinct: Extant species are still alive; extinct species are no longer in existence.

• Sister Species: Closely related species that share a common ancestor.

• Example: Loxodonta loxodonta (Asian elephant) and Loxodonta africana (African elephant) are sister species.

Phylogenetic Structures

• Simple Phylogeny:

  • An entire branch represents one species.

  • Example diagram segments (A, B, C, D, E) indicate species with connections without intersection or branching.

  • Dotted line indicates extinct species.

  • Most Recent Common Ancestor (MRCA): The ancestor shared by sister species.

• Monophyletic Groups:

  • A group consisting of a common ancestor and all its descendants.

  • Important for understanding evolutionary history:

    • Similarities amongst species should be due to common ancestry.

    • Differences arise from new evolutionary innovations.