Classification & Phylogeny

General Zoology LS2014 Donald Winslow 31 January 2011 Classification & Phylogeny Hickman, Cleveland P., Jr.; Larry S. Roberts; Susan L. Keen; David J. Eisenhour; Allan Larson, and Helen l'Anson 2011. Integrated Principles of Zoology, 15th ed., McGraw-Hill, NY. Ch. 10 pp 199-211, 213-214.

Approaches to classification • Taxonomy (Linnaeus) • Classified by similar characters • Phenetics • Quantitative approach based on similarity • Systematics (cladistics) • Based on phylogeny (patterns of descent) • Evolutionary taxonomy • Incorporates phylogeny and similarity

Taxonomic Hierarchy Kingdom Phylum Class Order Family Genus Species

Binomial nomenclature • Scientific name of a species italicized • 1st letter of genus name is capitalized • Specific epithet is all lower-case • Examples: • Homo sapiens (human) • Sciurus niger (fox squirrel) • Branta canadensis (Canada Goose) • Junco hyemalis (Dark-eyed Junco)

Subspecies • A subset (lower-order taxon) of a species • Trinomial nomenclature • Example: Junco hyemalis mearnsi

Type specimens & authority • Characteristics of a species were historically defined by “type” specimens kept at museums. • The taxonomist who names a species is the authority for that species. The name of the authority is often given with the scientific name of the species. • Example: Carduus nutans Linnaeus • (musk thistle)

Ancestral & derived characters • A character is a morphological feature or other aspect of phenotype. • An ancestral character is one that was present in the ancestors of a taxon. • A derived character is one that appeared during the evolution of a taxon.

Homology and homoplasy • A homologous character is one that is similar between two taxa because of common descent. • A homoplasic (analogous) character is one that is similar between two taxa because of convergent evolution.

Cladistics • Nested hierarchy of lineages within clades • Compared with outgroup • Synapomorphies useful to define clades • Cladogram shows only extant species. • Phylogenetic tree includes ancestors. • Parsimony used to choose cladogram. • Sources of phylogenetic information

Synapomorphy • Derived character • Shared by all members of a clade

Parsimony • The simplest explanation that is consistent with the evidence is the most likely to be correct. • Not necessarily likely to be correct! • The cladogram that assumes the fewest character transitions is the most parsimonious. • Characters may be morphological, biochemical, behavioral, cytological, etc.

Biochemical cladistics • Uses comparative approach • Derives phylogenies from DNA sequences • Hickman et al. Pp 210-211 Hickman, Cleveland P., Jr.; Larry S. Roberts; Susan L. Keen; David J. Eisenhour; Allan Larson, and Helen l'Anson 2011. Integrated Principles of Zoology, 15th ed., McGraw-Hill, NY.

Types of taxonomic classification • Monophyly • A monophyletic taxon includes the common ancestor of all members of the taxon and all descendants of that common ancestor. • Paraphyly • Includes the common ancestor and some, but not all, descendants of that common ancestor. • Polyphyly • Does not include the common ancestor.

Clades & grades • Examples • Penguins • Apes & humans

Sister taxa • A taxon’s sister taxon is the one that shares the most recent common ancestor.

Species concepts • Basic criteria • Common descent • Smallest distinct groupings • Interbreeding • Typological species concept • Biological species concept • Evolutionary species concept • Phylogenetic species concept

Typological species concept • Fixed & essential features • Defined by type specimen

Biological species concept • Interbreeding population • Reproductively isolated from other populations • Does not work well for asexual species

Evolutionary species concept • Isolated from other populations • Distinct evolution and fate • Works for asexual species

Phylogenetic species concept • Irreducibly distinct from other groups • Also works for asexual taxa • Often involves splitting taxa into separate species

Classification & Phylogeny