Bio 1B: Lec 6: Reading Trees

Sister groups

Branches that share a node

Monophyletic Group/Clade

ancestor + all descendants

What matters in a cladogram?

Topology (branching pattern, MRCAs) matters

Tip order and branch lengths do not matter unless the diagram says it means smth

Monophyletic/Clade

Mono- = alone

-phyletic = genus/species

Genus = group of species

Monophyletic is a single genus

Paraphyletic

Para- = beside/near

Paraphyletic means ancestor + some descendants, but excludes at least one lineage

Polyphyletic

Poly- = many

Polyphyletic means distantly related taxa grouped without MRCA

Character

A feature/trait that can vary

Character state

A particular condition of that character (absent v present, tall v short, etc.)

What can diagnose clades?

Shared derived states

Unique derived states can only identify one taxon and do not resolve relationships

Synapomorphy

Syn- = shared

Apo = novel/new

Morphy = Trait

shared derived (new) trait that diagnoses a clade

Symplesiomorphy

Sym = shared

plesio = ancestral

Morphy = trait

shared ancestral trait, can mislead if used to define smaller groups

Autapomorphy

Aut = self (automatic)

Apo = Nove/new

Morphy = trait

unique derived trait in one taxon, useful for identification, less useful for relationships

Outgroups

oldest/most different

helps us know which traits are ancestral cuz outgroups have all ancestral traits

Homology

Homo = same/similar

Logy = relation

Similarity due to shared ancestry

Homoplasy

Homo = same/similar

Plasy = shape

similarity not due to common ancestry, CONVERGENCE

Reversal

Losing the derived trait

How to distinguish synapomorphy form convergence

Map traits onto trees