Chapter 22

SYSTEMATICS – BIODIVERSITY + EVOLUTION

Taxonomy – naming, describing, and classifying organisms

•Naming:•Worldwide system recognized by all scientists•Binomial nomenclature -1st developed by Carolus Linnaeus•2 part name: Genus + specific epithet = scientific name•Genus name capitalized; species name not; both underlined or italics; both derived from Latin or Greek

Classifying – group organisms into meaningful categories• Taxon – group (pl. taxa) – Linnaeus also established a hierarchy• Kingdom, phylum, class, order, family, genus, species

• Currently we include a larger category above kingdom – domain• (Dumb King Phillip came over for good spaghetti)• We have three domains:• Eubacteria (aka bacteria) prokaryotes• Archaea • Eukarya – plants, animals, protists, fungi

• New proposal – group organisms into clades – a set of organisms with a common ancestor (more on this later)• Important – Figure 22-3 + Table 22-2, page 424

The three domains

Common ancestorof all living organisms

DomainArchaea

DomainEubacteria(bacteria)

DomainEukarya

The six-kingdom system of classification

Eubacteria Archaebacteria Protista Plantae Protista Animalia Fungi

Common ancestorof all living organisms

Common ancestorof all eukaryotes

Phylogeny – using systematics to describe the evolutionary history of life on Earth

• Based on available data – changed to adjust to new information•Homology – helpful similarities • Structures that are found in 2 or more groups that share a recent common ancestor• Example: wing of a bat and a bird•Homoplasy – not helpful similarities• Superficial similarity due to convergent evolution rather than descent from a common ancestor• Example: wing of a bird and a butterfly• The difference between these is not always easy to see

So, we want to make an evolutionary ‘family tree’…

• The branches use two set of features:• Shared ancestral characters – plesiomorphic characters• Found in all descendants from a particular ancestor (everyone on that ‘branch’)• Example: vertebral column – all vertebrates have this

• Shared derived characters – synapomorphic characters• Found in 2 or more taxa with a recent common ancestor (smaller ‘branches’)• Example: middle ear bones found in all mammals; identifies the branch between reptiles and mammals

Can we use molecular information? Of course!•Molecular systematics compares macromolecules, especially DNA, RNA, and amino acid sequences•Molecular clocks can be used to establish how long 2 groups have been evolving separately from each other (assuming a constant rate of change)•rRNA sequences – have been studied extensively and used as molecular clocks

Three kinds of taxonomic groupings:1. Monophyletic taxon• Ancestral species and all its descendants (see figure

22-6a p 428)• Example: mammals

2. Paraphyletic taxon• Common ancestor and some but not all descendants• Not used in cladistics• Example: reptiles – because birds are in a separate

taxon despite the fact that they share a common ancestor with reptiles

3. Polyphyletic group • ‘accidentally’ put organisms in groups even though

they do not share a common ancestor, perhaps because of homoplastic features • Example: the Protista Kingdom• This is avoided in cladistics because it does not show

evolutionary relationships

Evolutionary relationshipsTaxon III

Commonancestor

Common ancestorto groups 4, 5, and 6

Common ancestorto groups 5 and 6

Common ancestorto all groups

Common ancestorto all groups except 1

Commonancestorto groups2 and 3

A

B

D

EC

1 2 3 4 5 6

Taxon I "Taxon II"

Two approaches to the classification of reptiles birds, and mammals.

Mam

mal

s

Liz

ard

s

Sn

akes

Cro

cod

iles

Din

osa

urs

Commonancestor

Bir

ds

Reptiles

Two approaches to the classification of reptiles birds, and mammals.

A

B

D

EC

Mam

mal

s

Liz

ard

s

Sn

akes

Cro

cod

iles

Din

osa

urs

Commonancestor

Bir

ds

Reptiles