Taxonomy & Phylogeny Classification of Organisms

ClassificationClassification 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 Catagorization

Wittiker’s 5 Kingdom Classification Scheme

Taxonomic Rules Binomial nomenclature –Genus species –Genus name is a noun –species name is an 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 Amniotes – animals that have an 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

Example of Polarity Determination MammalsBirdsReptiles teeth no teeth Amniotic Amphibians &Fish Non-Amniotic Since outgroup has teeth, teeth are ancestral and would be presumed to be in found 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 teeth Common Ancestor

CladogramsCladograms Clade –Groups of organisms which 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

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