phylogeny

Phylogeny Phylogeny (Greek: phylon (tribe) and genesis (birth)) =

classification of organisms using “trees” to order ancestors → descendants

Taxonomy = practice of identifying

& categorizing organisms o classification schemeo historically based on

morphological featureso not necessarily an

evolutionary implication

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Systematics = scientific study of biological diversity in an evolutionary contexto includes: morphological, molecular genetic, biochemical, physiological,

ecological traitso CLADISTICS is a form of biological systematics that classifies

organisms into hierarchical monophyletic groups. For statistical hypothesis testing → SIMPLEST TREE- size of clades will vary- more characters will “strengthen” the tree

ancient modern

Graham et al. 2009

Monophyletic group is a taxon (group of organismsorganisms) which forms a clade, meaning that it consists of an ancestor and all its descendants.

Monophyletic group is a taxon (group of organismsorganisms) which forms a clade, meaning that it consists of an ancestor and all its descendants.

Monophyletic groupMonophyletic group

Derived Characters

primitive and derived are relativeand only have meaning when placed in context shared, derived characters = synapomorphies a derived character in one group might be primitive in another e.g., fur among tetrapods (4-footed vertebrates) = derived, but…

fur among mammals = primitive

Shared derived characters

Character: any feature exhibited by a taxon Homologous characters are used to construct cladorgrams

Shared primitive character: homology common to a more inclusive taxon Shared derived character: a unique evolutionary novelty in a clade

All similar characters

Analogous

HomologousAncestral

Derived

Example: backbone vs hair• not all animals posses hair, but all mammals –who have hair as a unique character also have a backbone, a trait shared with all other vertebrates

Constructing a Phylogeny

Select a focal group

Identify characters to be used in the analysis- ancient vs. derived

Determine the outgroup (i.e., the group that most closely resembles the ancient condition)

Construct a phylogenetic tree

ParsimonyThe simplest explanation consistent with the data.The smallest number of evolutionary changes needed to explain a phylogenetic tree (cladogram).

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Phylogenetic trees are hypothesis .

Phylogenetic trees are hypotheses

Sometimes most parsimonious tree does not reflect a true phylogeny.

There are more shared primitive characters between lizards and birds, than birds with mammals.

Remember… Ancient/primitive SIMPLE!!

A character can NOT be gained → lost → gained…

Focus on conserved cf. plastic character traits - flower color is plastic: mutates → changes readily from one

generation to the next

THINK OUTSIDE THE BOX…!!

OUTGROUP

Examples

OUTGROUP