Classification & PhylogenyGeneral Zoology LS2014

Donald Winslow31 January 2011

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