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Classification & Phylogeny
General Zoology LS2014
Donald Winslow
31 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
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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
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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
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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