Taxonomy & Phylogeny 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

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

Wittiker’s 5 Kingdom Classification Scheme

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

teethteeth

teeth

no teeth

MammalsBirdsReptiles

Amniote

Amphibians&Fish

Non-Amniote

• 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

teeth

Common Ancestor

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

Fig. 32.7