Classification of Organisms 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 Fig. 10.CO

Hierarchical Classification System Taxa Major groupings or categories Nested set of increasing inclusiveness Domain Kingdom Phylum Class Order Family Genus Species

Cladistic Tree of Life Fig. 10.11

Wittiker’s 5 Kingdom Classification Scheme Fig. 10.12

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 Amphibians &Fish Mammals Birds Reptiles no teeth teeth teeth teeth Non-Amniote Amniote Common Ancestor teeth 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

Cladograms Clade Synapomorphy Cladogram 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 Fig. 10.4

Cladograms vs Phylogenetic Trees 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 Comparison of cytochrome c mutations Human Fig. 10.5

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 Fig. 10.6

Cladistics & Cladograms vs Traditional Taxonomy Taxonomic groupings based solely on establishing monophyletic relationships Cladograms establish monophyletic taxonomic levels Traditional taxonomy Common descent – phyletic relationship Adaptive evolutionary change – ecological zones

Fig. 32.7

Fig. 10.9