BSCI Topic 8: The Tree of Life –Phylogenetic Reconstruction

1. Monophyletic groups (e.g., mammals)

.a.  Group has a unique common ancestor and includes all descendant groups

b.  United by derived similarity

Common ancestor + all descendants.

2. Polyphyletic groups (e.g., birds + bats)

a.  Don’t share a unique recent common ancestor

b.  United by convergent similarity

Unrelated organisms grouped by traits, not ancestry.

3.  Paraphyletic groups (e.g., “reptiles”)

a.  May have common ancient ancestor, but group does not include all descendant groups

b.  United by primitive similarity

Common ancestor, not all descendants.

a.  Phylogeny

the study of evolutionary histories and relationships among species or groups of organisms, essentially mapping out the "family tree" of life

1) The branches and connections on the tree of life that reflect the changes that have occurred over evolutionary time (phylogenetic tree)

(2)  Produced by two (or more) kinds of evolutionary processes (know what these are and what these terms mean):

(i) speciation (cladogenesis)

(ii) origin of new characteristics within a lineage over time (anagenesis)

Speciation (Cladogenesis)

process where a single ancestral species splits into two or more distinct daughter species, increasing taxonomic diversity.

Branching evolution (new species form).

Anagenesis

model of evolution in which a single species transforms into a new one without any branching, gradually replacing the ancestral lineage.

b.  Cladogram

Diagram showing evolutionary relationships.;

A branching diagram depicting an estimate (hypothesis) of the phylogeny

Synapomorphy

Shared derived trait (defined a clade)

Simplesiomorphy

Shared ancestral trait

Derived Evolution

refers to the concept of derived traits, which are novel characteristics that arise in a lineage and are different from those of its ancestors

Convergent evolution

Similar traits evolved independently (e.g., wings in bats and birds)

Primitive/Ancestral Similarity

traits shared by different organisms because they were inherited from a common ancestor

Outgroup

Related group used to determine ancestral traits

Parsimony

Simplest evolutionary explanation preferred

6.  Monophyletic groups can be recognized using two methods:

a.  Outgroup analysis (monophyletic from paraphyletic)—understand 

b.  Parsimony (monophyletic from polyphyletic)—understand

Ultimate Goal:

to find monophyletic groups and exclude polyphyletic and paraphyletic groups 

a.  To understand the group's true evolutionary history

b.   To get our taxonomy/classification in synch with our knowledge of their evolutionary history