BIOL 112 Lab Exam 1 Lab 2

Systematics

The branch of biology that explains evolutionary relationships between organisms and what led to those relationships.

Two sub-disciplines of Systematics

Taxonomy and Phylogeny.

Taxonomy

The study of describing, identifying, naming, and grouping organisms.

Why can taxonomy change?

Taxonomic classifications change when new scientific evidence becomes available.

Phylogeny

The study of evolutionary relationships and creating tree-like diagrams based on ancestry.

Evidence used to build phylogenies

Morphology, fossil evidence, embryonic development, and DNA.

Cladistics

The method used to build and interpret phylogenetic trees based on shared characteristics.

Basic Cladistics

The concept that natural selection can produce distinct species as organisms acquire enough adaptive characteristics.

Cladogram

A branching diagram representing a hypothesis about how different groups or species are evolutionarily related.

Phylogeny

A branching diagram representing a hypothesis about evolutionary relationships among organisms.

What does the Y-axis of a cladogram represent?

Time.

Character (Trait or Characteristic)

An observable feature of an organism that has different states, such as presence or absence.

Character State

The specific form or condition of a character, such as presence or absence of legs.

Ancestral Character

A trait that matches the characteristics of the common ancestor.

Derived Character

A new trait that the common ancestor did not possess.

Example of an ancestral character state

Fish having an absence of legs.

Example of a derived character state

Gecko having the presence of legs.

Ingroup

The group of related organisms being studied.

Outgroup

A closely related group outside the ingroup that is used for comparison.

Purpose of an outgroup

To provide a comparison and help identify ancestral character states.

Where does the outgroup branch on a cladogram?

It branches off earlier than the group of interest and is always the first branch.

What traits does the outgroup have?

It has the ancestral traits for the characteristics being studied.

Is the outgroup the ancestor?

No. The outgroup is a related group used for comparison, not the actual ancestor.

Platypus as an outgroup

The platypus can serve as an outgroup because it branches off early and has ancestral traits for certain characteristics.

Node

A branching point representing the last common ancestor of all branches beyond it.

Taxon

A named group of organisms; the plural is taxa.

Clade

A group of organisms that share a common ancestor.

Sister Taxa

Two taxa that share a particular common ancestor and are on either side of a split.

Cladogenesis

The process in which one species splits into two different species.

Sister Taxa on a cladogram

The species or groups located on either side of a split from a common ancestor.

Apomorphy

A new, derived character state that appears after a lineage develops it.

What happens to an apomorphy after it develops?

It is present in all species that branch off after its development, but absent from earlier branches.

Two types of Apomorphy

Autapomorphy and Synapomorphy.

Autapomorphy

A derived character state unique to a single species.

Synapomorphy

A derived character state shared by two or more related species.

Plesiomorphy

A primitive character state inherited from a common ancestor.

What happens to a plesiomorphy on a cladogram?

It is shared by taxa until it is replaced by a derived character state.

Monophyletic

A clade containing a common ancestor and all of its descendants.

Examples of monophyletic groups

Mammals and canines.

Paraphyletic

A group containing a common ancestor and some, but not all, of its descendants.

Why is Reptilia considered paraphyletic?

It excludes birds, even though birds evolved from within the reptilian lineage.

How should birds be grouped with Reptilia?

Birds should be included with reptiles because they share the relevant common ancestor.

Polyphyletic

A group containing organisms from multiple separate lineages with different ancestors.

Is polyphyletic considered a valid clade?

No. Polyphyletic groups are not considered valid clades.

Why are polyphyletic groups often formed?

They may group organisms based only on similar external appearances.

Convergent Evolution

When unrelated organisms independently evolve similar traits, often causing them to look similar.

Example of a polyphyletic group

Animals that fly may be grouped together despite having separate evolutionary origins.

Difference between ancestral and derived traits

Ancestral traits were present in the common ancestor; derived traits evolved later in a lineage.

Difference between apomorphy and plesiomorphy

Apomorphy is a new derived character state; plesiomorphy is a primitive ancestral character state.

Difference between autapomorphy and synapomorphy

Autapomorphy is unique to one species; synapomorphy is shared by two or more related species.

Difference between monophyletic and paraphyletic

Monophyletic includes the ancestor and all descendants; paraphyletic includes the ancestor but excludes some descendants.

Difference between paraphyletic and polyphyletic

Paraphyletic includes one ancestor but not all descendants; polyphyletic combines lineages from separate ancestors.

Character Matrix

A table containing all characteristics and taxa of interest, used to construct a phylogenetic tree.

What information is used to construct a character matrix?

All available information, including traits and DNA.

How is a character matrix filled in?

With 1s and 0s representing character states.

What does 1 mean in a character matrix?

The taxon has the derived character state (apomorphy).

What does 0 mean in a character matrix?

The taxon has the ancestral character state (plesiomorphy).

Parsimony

The principle of choosing the hypothesis that requires the fewest assumptions.

Why is parsimony used in phylogenetics?

Multiple phylogenetic trees can be constructed, so parsimony helps select the best-supported tree.

What does parsimony favor in cladistics?

The cladogram requiring the fewest changes in character traits.

How should derived characters generally appear under parsimony?

A derived character should arise only once, with organisms possessing it sharing a common ancestor.

What pattern should generally be avoided under parsimony?

A trait appearing, disappearing, and then reappearing independently.

Convergent Evolution

The evolution of similar traits independently in different groups without a common ancestor for that trait.

Analogous Traits

Similar traits that evolved independently in different groups without a common evolutionary origin.

Relationship between convergent evolution and analogous traits

Convergent evolution can produce analogous traits because similar traits evolve independently without a common ancestor.

Why can convergent evolution complicate parsimony?

Different groups may independently evolve similar traits, causing the same character to appear multiple times.