Download Chapter 18 Systematics

Systematics: Seeking
Order Amidst Diversity
Chapter 18
Systematics
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Systematics is the branch of biology
concerned with
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Reconstructing phylogeny (evolutionary history)
Naming organisms and placing them into
hierarchical categories based upon their
evolutionary relationships
Major Categories of Classification
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The eight major categories of classification, in
order of decreasing inclusiveness are
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Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Scientific Names
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The scientific name of an organism is
formed from the genus and species
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The genus Sialia (bluebirds) includes three
species:
 Sialia sialis (the eastern bluebird)
 Sialia mexicana (the western bluebird)
 Sialia currucoides (the mountain bluebird)
The Origin of Classification
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Aristotle (384-322 B.C.)
Was among first to develop a standardized language for
naming organisms
 Classified about 500 organisms into 11 hierarchical
categories based on various characteristics
Carolus Linnaeus (1707-1778)
 Laid the groundwork for the modern classification system
 Placed organisms into hierarchical categories based on
their resemblance to other organisms
 Introduced the scientific name composed of genus and
species
Charles Darwin (1809-1882)
 Published On the Origin of Species, which demonstrated
that all life is related by common ancestry
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Evolutionary Relationships
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Biologists realized that taxonomic categories
should reflect evolutionary relatedness
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The more categories two organisms share, the
closer their evolutionary relationship
All organisms share certain similarities
Similarities result from common ancestry or
convergent evolution
Present-Day Classification
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Systematists determine evolutionary
relationships based on similarities due to
common ancestry
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Similarities may be anatomical or molecular
Anatomical similarities
Systematists examine similarities in external
body structure
Systematists examine similarities in internal
body structures, such as skeletons and
muscles
Anatomical Similarities
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Systematists examine microscopic similarities
to discern finer details
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Number and shape of the “teeth” on the tonguelike radula of a snail
Shape and position of the bristles on a marine
worm
External structure of pollen grains of a flowering
plant
Molecular Similarities
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Systematists examine genetic similarities
between:
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DNA nucleotide sequences
Chromosome structure
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It has been estimated that 99% of the chimpanzee
genome is identical to that of humans
The Two-Kingdom System
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Before 1969, all forms of life were classified
into two kingdoms
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Animalia
Plantae (included plants, bacteria, fungi and
photosynthetic eukaryotes)
The Five-Kingdom System
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Proposed by Robert H. Whittaker (1969)
Kingdoms include
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Monera (all prokaryotes)
Plantae
Fungi
Animalia
Protista (eukaryotes that are not plants, fungi, or
animals)
The Three-Domain System
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Introduced by Carl Woese (1990)
Discovered that kingdom Monera included
two very distinct groups (Bacteria and
Archaea) based on nucleotide sequences of
ribosomal RNA
Domains include
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Bacteria (prokaryotic)
Archaea (prokaryotic)
Eukarya (eukaryotic)
Kingdom-Level Classification
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Systematists have yet to reach a consensus
about the precise definitions of new
prokaryotic and eukaryotic kingdoms
Figure 18-6, p. 364, shows the evolutionary
relationships among some members of the
domain Eukarya…
How Many Species Exist?
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Biodiversity is the total number of species in
an ecosystem
Number of named species is currently about
1.5 million (biased toward large organisms in
temperate regions)
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5% prokaryotes and protists
22% plants and fungi
73% animals
Estimated that 7 million to 10 million species
may exist
How Many Species Exist?
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Between 7,000 and 10,000 new species are
identified annually, mostly in the tropics
Tropical rain forests are believed to be home
to two-thirds of the world’s existing species,
most of which have yet to be named
Because tropical rain forests are being
destroyed so rapidly, species may become
extinct before we ever knew they existed