Taxonomy and Classification The Six Kingdoms. Archaebacteria.
Taxonomy Five Kingdoms
Transcript of Taxonomy Five Kingdoms
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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