Introduction to Systematics
Principles of Biology II

Systematics and Phylogeny:Uncovering patterns of evolution
Classification of life's diversity
Takes evolutionary relationships into account

How shall we classify it? Systematics
Systematics = anaytical approach to understanding diversity and relationships of organisms (present-day and extinct)

Taxonomy: identification and classification of species (a part of systematics)

Phylogenetics: classification based on evolutionary history

Phylogenies based on

Records derived from
living organisms


Taxonomy - employs the Linnaean system

Carolus Linnaeus: 18th century Swedish botanist
Contributions include
Two part naming system
Hierarchical classification

Before Linnean system
Tradescantia ephemerum phalangoides tripetalum non repens Virginianum gramineum
"The annual upright Tradescantia from Virginia with a grasslike habit, three petals, and stamens with hairs like spider legs"
Tradescantia virginiana

1. Binomial nomenclature
Genus (capitalized) followed by specific epithet (lower case)
Italics or underlined
Latin/Latinized (Ochisme, Marichisme, Peggichisme)

Improvement over common name b/c...

Homo sapiens
Magnolia grandiflora

Problems with common names
In Minnesota - Red squirrel

In Colorado - Chickaree

2. Hierarchical system (Fig. 26.3)

Objectives of Taxonomy
distinguish close relatives
arrange into broader categories

Phylogenetics (another part of systematics)
Definition: classification system based on evolutionary relationships

Figure 26.4 The connection between classification and phylogeny

Uses Cladistics techniques

Build a cladogram (evolutionary tree)
Descent from common ancestor in which new trait evolved
Branch = group with shared characteristic: synapomorphy

Nested classification

Characteristics continue to change

Cladistics and taxonomy

Figure 26.11 Constructing a phylogenetic tree




Things to watch out for:Homology vs. analogy
In constructing a phylogeny: distinguish whether a similarity is the result of homology or analogy
Homology is similarity due to shared ancestry
Analogy is similarity due to convergent evolution
Homoplasy- analogous structure

Clades can be nested in larger clades, but not all groupings or organisms qualify as clades

A valid clade is monophyletic, signifying that it consists of the ancestor species and all its descendants
LE 26-10a

A paraphyletic grouping consists of an ancestral species and some, but not all, of the descendants
LE 26-10b

A polyphyletic grouping consists of various species that lack a common ancestor
LE 26-10c
Shared Primitive and Shared Derived Characteristics
In cladistic analysis, clades are defined by their evolutionary novelties

A shared primitive character is a character that is shared beyond the taxon we are trying to define
A shared derived character is an evolutionary novelty unique to a particular clade

An outgroup is a species or group of species that is closely related to the ingroup, the various species being studied
Systematists compare each ingroup species with the outgroup to differentiate between shared derived and shared primitive characteristics

Outgroup comparison assumes that homologies shared by the outgroup and ingroup must be primitive characters that predate the divergence of both groups from a common ancestor
It enables us to focus on characters derived at various branch points in the evolution of a clade

On Mastering Biology
Complete Investigations Ch 26 on cd "How is Phylogeny Determined bu Comparing Proteins?"(do not submit for a grade)