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Taxonomy & Phylogeny. Classification of Organisms. Classification. What characters are suitable for classification Systematics Combination of taxonomy & phylogeny Systematic approach to understanding evolutionary relationships among organisms. Hierarchical Classification System. Taxa
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Taxonomy & Phylogeny Classification of Organisms
Classification • What characters are suitable for classification • Systematics • Combination of taxonomy & phylogeny • Systematic approach to understanding evolutionary relationships among organisms
Hierarchical Classification System • Taxa • Major groupings or categories • Nested set of increasing inclusiveness Domain Kingdom Phylum Class Order Family Genus Species
Taxonomic Rules • Binomial nomeclature • Genus species • Genus name is noun • species name is adjective • Higher taxonomic levels (families, orders, etc..) are also nouns
Taxonomy Relates to Phylogeny • Taxonomic characters allow phylogenetic grouping • Useful taxonomic characters • Morphological • Molecular (biochemical) • Chromosomal • Proteins • DNA • Homologies • Character similarities attributed to common ancestry
Using Taxonomic Characters to Construct Phylogenies • Ancestral character state • The form of the trait present in the most recent common ancestor of the groups being considered • Derived character state • The variant forms of the trait present in the members of the groups being considered • Polarity • Relationship of character trait state to ancestral state
Example of Polarity Determination • Study group • Amniotes – animals with amniotic membrane around developing embryo • Birds, Reptiles, Mammals • Character being studied • Dentition – teeth • Character states • Present • Absent • Question: Is dentition a derived or ancestral trait for amniotes? • Outgroup comparison • Phylogenetically close group, but non-amniote
Example of Polarity Determination Reptiles Birds Mammals Amphibians&Fish • Outgroup has teeth • therefore teeth are considered ancestral & be presumed to occur in most recent common ancestor of amniotes and non-amniotes • Teeth in amniotes is an ancestral character state • Loss of teeth in birds is a derived state no teeth teeth teeth teeth Non-Amniote Amniote Common Ancestor teeth
Cladograms • Clade • Groups of organisms that share derived character states • Synapomorphy • Shared, derived character • Cladogram • Nested, hierarchical assembly and representation of clades
Phylogenetic Relationships Established by Comparison of Multiple Characters
Cladograms vs Phylogenetic Trees • Cladogram • Lacks information • duration of lineages • Amounts of evolutionary change • Phylogenetic tree • Establishes extinct vs extant lineages • Indicates evolutionary timescale & degrees of change • Length of lines or numerical indications
Molecular Phylogeny Human • Comparison of cytochrome c mutations
Phylogenetic Groupings • Monophyletic • All descendents and most recent common ancestor • Paraphyletic • Leaves out some descendents from a recent common ancestor • Polyphyletic • Arbitrary groupings which do not include common ancestors
Cladistics & Cladograms vs Traditional Taxonomy • Cladistics • Taxonomic groupings based solely on establishing monophyletic relationships • Cladograms establish monophyletic taxonomic levels • Traditional taxonomy • Common descent – phyletic relationship • Adaptive evolutionary change – ecological zones
