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Taxonomy Five Kingdoms

R.H Whittaker1969

Three Domains

Cladistics:Cladograms andmolecular data

Evolutionary Trees

What are the tools used by scientiststo observe and understandevolutionary relationships?

• 1. Artificial selection• 2. Fossil record• 3. Comparative anatomy• 4. Comparative embryology• 5. Comparative biochemistry• 6. Biogeography

Artificial Selection

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The fossil record: A gallery of fossils Homologous structures: anatomical signs of descent withmodification

What about analogousstructures?

• Convergent evolution• Co-evolution

Comparative Embryology:

• “Ontogeny recapitulatesphylogeny” - theappearance of ancestralstructures in the embryosof modern descendants(Haeckel)

Molecular Data and the Evolutionary Relationships ofVertebrates Biogeography - Wallace’s line

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Evidence from biogeographicalstudies:

Some major episodes in the history of life

Systematics: connecting phylogenyand taxonomy

• Taxonomy = the science of classifyingorganisms

• Phylogenetics = the study of phylogeny, or thehistory of evolutionary relationships amongspecies

Figure 25.8 Taxonomy starts with the latin binomial, and exhibits a hierarchicalstructure reflecting phylogenetic relationships among taxa or groups of organisms

Latin “binomial” ortwo-part name(genus and species)

Figure 25.9 The connection between classification and phylogeny: this phylogenetic treeorganizes taxa into a hypothesized tree of evolutionary relatedness, with species at the

tips of the branches.

How are thesephylogenetictreesconstructed?

Traditional Approach:Phenetics

Classifications basedon perceived overallsimilarity

Perceived similarities can be misleading

Jellyfish Starfish Human

Which pair is most similar?Which pair is most closely related?

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Perceived similarities can be misleading

Jellyfish Starfish Human

• Live in water• No backbone

• Live on land• Have backbone

Perceived similarities can be misleading

Jellyfish Starfish Human

Classification based on phylogeny

• Phylogeny = patterns of ancestry• Cladistics introduced by Willi Hennig in

1950’s

Classification based on phylogeny

• Phylogeny = patterns of ancestry• Cladistics introduced by Willi Hennig in

1950’s• Goals of cladistics:

– Base classifications on phylogeny– Recognize continuum of evolution– Make taxonomists “show their work”, make

explicit hypotheses based on data theypresent

Key principles of cladistics• Since organisms are related by descent, close

relationship implies recent common ancestors.• Organisms differ genetically and pass on these

differences (and resultant traits) to their ancestors.• Therefore, organisms which are closely related

should share new features, acquired by evolution,that are not present in other groups.

• These uniquely shared derived characters are thebest guide to the evolutionary sequence.

The more DERIVED characterstwo lineages share, the more

closely related they are.

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Derived characters are identifiedthrough comparison with an

outgroup.

• An outgroup is a taxon known (orassumed) to have diverged from acommon ancestor less recently thanany of the other taxa we wish toclassify– Relies on other studies, theory, or

intuition

Derived characters are identifiedthrough comparison with an

outgroup.

• An outgroup is a taxon known (orassumed) to have diverged from acommon ancestor less recently than any ofthe other taxa we wish to classify

• Then derived characters are those whichare found in some of the taxa underconsideration but not the outgroup.

Adding an outgroup to our comparison

Jellyfish Starfish HumanSponge

Derived characters must be absentfrom outgroup

Sponges, jellyfish, and starfish all live in waterand do not have backbones, therefore these areNOT derived characters.

Jellyfish Starfish HumanSponge

Derived characters found in only onetaxon set it apart

Backbones and living on land are unique tohumans.

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Derived characters found in only onetaxon set it apart

Jellyfish Starfish HumanSponge

backbone

Derived characters found in all taxa donot resolve relationships

Sponges have only one tissue layer.The other taxa all have multiple tissue layers.

Derived characters found in all taxa donot resolve relationships

Jellyfish Starfish HumanSponge

multiple tissue layers

Shared, derived characters grouprelated taxa together

Sponges and jellyfish lack enclosed body cavities.(ancestral)Starfish and humans have enclosed body cavities.(derived)

Shared, derived characters grouprelated taxa together

Sponges and jellyfish lack enclosed body cavities.(ancestral)Starfish and humans have enclosed body cavities.(derived)Shared derived characters are called SYNAPOMORPHIES.

Shared, derived characters grouprelated taxa together

Jellyfish Starfish HumanSponge

multiple tissue layers

enclosed body cavities

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We have just made a cladogram

• Phylogenetic tree showing the orderin which different lineages divergedfrom a common ancestor

We have just made a cladogram

• Phylogenetic tree showing the orderin which different lineages divergedfrom a common ancestor

• Each branch point is labeled with (a)diagnostic synapomorphy(ies)– This is what allows others to “check our

work”

We have just made a cladogram

• Phylogenetic tree showing the order inwhich different lineages diverged from acommon ancestor

• Each branch point is labeled with (a)diagnostic synapomorphy(ies)

• Each synapomorphy is found on onebranch of the tree but not the otherbranch

Synapomorphies mark each branch ona cladogram

Jellyfish Starfish HumanSponge

multiple tissue layers

enclosed body cavities

Figure 25.10 Note: Legitimate taxa, such as genera or families, are composed ofmonophyletic groups of species. These represent evolutionarily unified groups.

•Monophyletic groups contain a common ancestor and all of its descendants.

•Paraphyletic groups are missing one or more descendants, and polyphyleticgroupings are missing a common ancestor.

•How do we construct hypothesized monophyletic groups? Using shared,derived, homologous traits.

What are shared, derived,homologous traits?

• Shared traits are similarities among organisms• Some similarities are homologous, i.e. shared

because of inheritance from a commonancestor

• Other similarities are analogous, i.e. due toconvergent evolution, NOT from inheritancefrom a common ancestor

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Algae Fern Pine Cherry

Lives on land

Woody Stem

Flowers

Photsoynthesizes

Algae Fern Pine Cherry

Lives on land

Woody Stem

Flowers

PhotsoynthesizesAncestral trait shared by all 4 taxa

Algae Fern Pine Cherry

Lives on land

Woody Stem

Flowers

“broad leaves”“broad leaves”

Algae Fern Pine Cherry

Lives on land

Woody Stem

Flowers

Loss of “broad leaves”

“broad leaves”

wings wings

salamander hawk squirrel bat What it means if a taxa has anancestral trait

• For the character under question, the state ofthe character matches the character state inthe outgroup

• E.g., ferns display the ancestral trait for thecharacter state: does it have woody stem

• This does not mean that the fern is theancestor to any of the other taxa