Systematics

Taxonomy, Phylogeny, and Classification

Diversity of Life

Diversity of Life

• How do we organize it all?– MORPHOLOGY

• What the organisms look like (phenotype).

– EVOLUTIONARY HISTORY• Shared ancestry, relationships.• CLUES:

–Space – Biogeographic distributions of organisms

–Time – Fossil record

Systematics

• Science of organizing the diversity of life.

1. Taxonomy – Identification & Naming

2. Phylogeny – Analyzing evolutionary relationships among groups.

3. Classification – Placing organisms into an organized categorization scheme.

Taxonomy

• Identification & Naming• Taxon: a group of organisms (Taxa)• “Species” – basic group, the only REAL

taxon.– Group of interbreeding populations that are

reproductively isolated from other such groups (and evolving independently of other such groups).

• Lineage – Taxa connected in time by genetic links.

Taxonomy• “Species” are not always easy to detect!

– Variation– Asexual reproduction– Morphology is not enough

• Need anatomy, physiology, ecology, behavior, biochemistry, evolutionary history, etc.

• Identified by experts in their respective fields.

Taxonomy• New species published in peer-reviewed

Journals.

Taxonomy• A “Type Specimen” is

denoted.– A single physical specimen

that all others are later compared to.

– The Latin description is based on this specimen.

– Stored in a special place.• ATCC:• http://www.bioscience.org/urlli

sts/atcc.htm

Taxonomy

• New species each given a “Scientific Name”– Carolus Linnaeus – Binomial Nomenclature– 2-word Latin name.

• Pinus strobus• Dictyostelium discoideum• Bubo virginianus

• “Common Names” also…– Can be misleading

Taxonomy

• Pinus strobus

• 1st word = Genus– A generalized name

• 2nd word = specific epithet– A descriptive name

• Always in italics or underlined.

• Genus is capitalized, epithet is lower case.

• Specific epithet never used alone!

Taxonomy

• “Variants” sometimes used– not different species, but “sub-species”– An additional descriptor is added to the end.

Lampropeltis triangulum var. sinaloae

Lampropeltis triangulum multistriata

Phylogeny• Grouping new species/taxa with closely-

related taxa from an evolutionary perspective.

• Phylogenetic Trees:

Phylogeny

Easier said than done!

3 approaches:1. Evolutionary Systematics

• Grouping based on similarities & differences• Reliance on fossil evidence• Subjective

2. Phenetics• Grouping based on similarities only• Convergence is a problem

Phylogeny

3. Phylogenetic Systematics (Cladistics)• Based on similarities derived from a

common ancestor – “Shared Derived Characters”(if only 1 in the group has the character, it’s no

good)

• Plesiomorphic vs Apomorphic characters• Want “Synapomorphies”• Identifies Monophyletic Groups• Look for homologous structures (not

analagous ones).

Phylogeny

• Tree Polarity – – Need to know which character state is

ancestral (plesiomorphic) and which is derived (apomorphic).

– Fossil Evidence is good, but not always available!

– Outgroup• A closely related organism that is NOT part of the

“ingroup” being studied.• Acts as a means of comparison.

Phylogeny

• Outgroups:

Phylogeny

• Must REALLY know your organism

• Often, genes are used to INFER relationships between whole organisms.

Phylogeny• Phylogenetic Trees

– Represent CURRENTLY LIVING organisms.

– DO NOT represent a This That That That

NOW!

Phylogeny of Animals

Classification

• Categorizing organisms into a hierarchy of names (hopefully) according to their relatedness.

• Historically – based on convenience.

• Starting at Species (the most exclusive group), organisms are grouped into more and more broad & inclusive Taxa.

• “Species” is the only level that really exists as an true single entity.

Classification

Kingdom

Phylum/Division

Class

Order

Family

Genus

Species

Animalia

Chordata

Mammalia

Primates

Hominidae

HomoHomo

sapiens

Animalia

Chordata

AvesMammalia

StrigiformesPrimates

TytonidaeHominidae

TytoHomo

Classification

Homosapiens

Tytoalba

Classification

• Meant to reflect phylogeny:

Classification• Times are changing!• Phylocode (http://www.ohiou.edu/phylocode/)

• Rankless Classification

• Clades are each given a name

Tree of Life

Systematics

• Tree of Life: http://tolweb.org/tree/phylogeny.html