Classification

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Chapter 18

• Classification

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Chapter 18 Mystery

• Page 509
• GRIN AND BEAR IT
• Hypothesis Are polar bears and brown bears
  separate species?

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Section 18.1Finding Order in Diversity

• Objectives
• What are the goals of binomal nomenclature and
  systematics?
• How did Linnaeus group species into larger taxa?
• Define
• Binomial nomenclature
• Genus
• Systematics
• Taxon
• Family
• Order
• Class
• Phylum
• Kingdom

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I. Assigning Scientific Names
Groundhog woodchuck

• To understand diversity must describe and name
  each species
• Each scientific name must refer to one and only
  one species
• Everyone must use the same name for that species
• Common names are confusing (mean different things
  in different countries)

Burro Donkey
Gnus Wildbeast Bearded Antelope
Puma Cougar Mountain lion panther
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• 18th century
• Assigned greek/latin names
• Describe species in great detail
• Names can be long? still confusing
• Difficult to standardize b/c different scientists
  focused on different characteristics
• Differences can be used to ID species using
  dichotomous key

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A. Binomial Nomenclature

• 1730s swedish botanist Carolus Linnaeus
  developed 2-word naming system
• In binomial nomenclature, each species is
  assigned a 2-part scientific name.
• Written in italic
• First word begins w/ capital letter genus to
  which org belongs
• Genus group of similar species
• Second word is lowercased unique to each
  species
• Species group of individuals capable of
  interbreeding and producing fertile offspring
• Often description of important trait or habitat

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B. Classifying Species into Larger Groups

• Scientists try to classify (organize) living and
  fossil species into larger groups that have
  biological meaning
• Systematics science of naming and grouping
  organisms
• The goal of systematics is to organize living
  things into groups that have biological meaning
• Groups taxa (singular taxon)

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Mystery Clue

• Page 512
• Polar bears and brown bears interbreed and
  produce fertile hybrids in zoos, but they very
  rarely interbreed in nature.
• What do you think this means about the
  relationship between them?

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II. The Linnaean Classification System

• Linnaeus developed classification system that
  organized species into taxa that formed a
  hierarchy (set of ordered ranks)
• Original system 4 levels
• Over time, Linnaeuss original classification
  system expanded to include seven hierarchial
  taxa species, genus, family, order, class,
  phylum, and kingdom
• 2 smallest categories genus species
• Grouped species according to anatomical
  similarities and differences ? placed into larger
  groups
• Example Camelus bactrianus (Camel)
• Camelus genus name
• bactrianus species name
• Camelus dromedarius (different species in same
  genus ? Camel with 1 hump)

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1. Family

• Group larger than genus
• Multiple genuses can be classified in the same
  family
• Example Lama glama South American llama
• Resembles Bactrian camels and dromedaries
• But more similar to other South American species
  than it is to European and Asian camels
• So different genus Lama
• Several genera that share many similarities
  grouped into larger group (family)
• Example Camelidae

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2. Order

• Closely related families grouped into next larger
  rank Order
• Example Camels and llamas (family Camelidae) ?
  grouped with several other animal families
• deer family Cervidae
• cattle family Bovidae
• order Artiodactyla (hoofed animlas with even
  number of toes)

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3. Class

• Similar orders grouped into next larger rank ?
  class
• Example order Artiodactyla placed in class
  Mammalia
• Includes all animals that are warmblooded, have
  body hair, and produce milk for their young

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4. Phylum

• Classes are grouped into a phylum
• Includes orgs that are different but share impt
  characteristics
• Example class Mammalia grouped w/ Birds (class
  Aves), reptiles (class Reptilia), amphibians
  (class Amphibia), and all classes of fish into
  phylum Chrodata
• All share impt body-plan features (nerve cord
  along back)

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5. Kingdom

• Largest and most inclusive taxonomic category
• All multicellular animals are placed in kingdom
  Animalia

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A. Problems with Traditional Classification

• Members of a species determine which orgs belong
  to that species by deciding w/ whom they mate and
  produce offspring
• Researchers define Linnaean ranks above the level
  of species b/c different groups have been defined
  in different ways at different times
• How to determine which similarities and
  differences are most important?
• Linnaeus chose characteristics carefully (century
  before Darwin)
• Modern systematists apply Darwins ideas to
  classification and try to look beyond simple
  similarities and differences and look to
  evolutionary relationships
• Today try to assign species to a larger group in
  ways that reflect how closely members of those
  groups are related to each other

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Section 18.2Modern Evolutionary Classification

• Objectives
• What is the goal of evolutionary classification?
• What is a cladogram?
• How are DNA sequences used in classification?
• Define
• Phylogeny
• Clade
• Monophyletic groups
• Cladogram
• Derived character

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I. Evolutionary Classification

• Phylogeny the evolutionary history of lineages
• The goal of phylogenic systematics, or
  evolutionary classification, is to group species
  into larger categories that reflect lines of
  evolutionary descent, rather than overall
  similarities and differences

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A. Common Ancestors

• Phylogenic systematics places orgs into higher
  taxa whose members are more closely related to
  one another than they are to members of any other
  group
• The larger a taxon is, the farther back in time
  all of its members shared a common ancestor

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B. Clades

• Clade group of species that includes a single
  common ancestor and all descendants of that
  ancestor (living and extinct)
• Clade must by monophyletic group includes
  single common ancestor and all of its descendants
  
• Some groups defined before advent of evolutionary
  classification monophyletic
• Some groups paraphyletic the group includes
  common ancestor but excludes one or more groups
  of descendants

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II. Cladograms

• Cladistic analysis compares carefully selected
  traits to determine order in which groups of
  organisms branched off from common ancestor
• Cladogram links groups of organisms together by
  showing how evolutionary lines (lineages)
  branched off from common ancestor

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A. Building Cladograms

• Speciation event one ancestral species splits
  into 2 new species basis of each branch point
  (node)
• Node represents last point at which the 2 new
  lineages shared a common ancestor
• Node splits a lineage into 2 separate lines of
  evolutionary ancestry
• Bottom (root) represents common ancestor shared
  by all orgs in cladogram
• Branching patterns indicate degrees of
  relatedness among orgs

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B. Derived Characters

• Cladistic analysis focuses on certain kinds of
  characters (derived characters) when assigning
  orgs to clades
• Derived character trait that arose in most
  recent common ancestor of a particular lineage
  and was passed along to its descendants
• Whether or not a character is derived depends on
  the level at which youre grouping orgs
• Example several traits shared by coyotes and
  lions (clade Carnivora) (clade Tetrapoda-4 legs)
  (clade Mammalia-hair)

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C. Losing Traits

• 4 limbs derived character of clade Tetrapoda
• Snakes (no limbs) but ancestors of snakes had 4
  limbs
• Trait for limbs was lost
• Distantly related groups of orgs can sometimes
  lose the same character ? systematists cautious
  about using absence of a trait as a character
• Whales do no have 4 limbs either, but snakes more
  closely related to other reptiles than they are
  to whales

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D. Interpreting Cladograms

• Lowest node represents last common ancestor of
  all 4-limbed animals (clade Tetrapoda)
• Forks show order in which various groups branched
  off from tetrapod lineage over course of
  evolution
• Position of characters reflect order in which
  those characteristics arose in lineage
• Derived characters that occur lower on
  cladogram than the branch point for a clade are
  not derived for that particular clade

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E. Clades and Traditional Taxonomic Groups

• True clad must be monophyletic contains
  ancestral species and all of its descendants
  (cant leave any out)
• Also cannot include any species not descendants
  of original ancestor
• Many traditional taxonomic groups do form valid
  clades
• class Mammalia corresponds to clade Mammalia ?
  all vertebrates w/ hair and other impt chars
• Some traditional groups do not form valid clades
• Todays reptiles all descended from common
  ancestor
• Birds also descended from same ancestor (not in
  class Reptilia)
• Reptilia w/o birds is not a clade
• Aves bird clade
• Dinosaura Reptilia clades reptiles birds
• Evolutionary biologists look for links b/w groups
  how each is related to others
• Bird also dinosaur, reptile, tetrapod, chordate

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III. DNA in Classification

• Cladistic analysis based largely on physical
  chars skeletons teeth
• Goal of systematics understrand evolutionary
  relationships of all life on earth
• Bacteria, plants, snails, apes
• No physical similarities, so how can they be
  related??

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A. Genes as Derived Characters

• All orgs carry genetic info in DNA passed from
  earlier generations
• Orgs share number of genes and show impt
  homologies used to determine evolutionary
  relationship
• Example eukaryotic cells have mitochondria all
  mitochondria have their own genes
• All genes mutate over time ? shared genes contain
  differences that can be treated as derived
  characters in cladistic analysis
• The more derived genetic characters 2 species
  share, the more recently they shared a common
  ancestor and the more closely they are related in
  evolutionary terms

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B. New Techniques Suggest New Trees

• Use of DNA characters helped make evolutionary
  trees more accurate
• Example African vulture vs. American vulture
  look alike and traditionally classified as
  falcons
• American vulture urinates on legs when
  overheated ? similar behavior to stork not
  African vulture
• Analysis of DNA American vulture more similar
  to storks than African vultures
• Suggests American vultures and storks more
  recent common ancestor than American and African
  vultures
• Molecular analysis powerful tool routinely used
  by taxonomists to supplement data from anatomy
• Example Giant panda red panda
• Share anatomical similarities w/ bears and
  raccoons
• Peculiar wrist bones that work like a human thumb
• DNA analysis giant panda shares more recent
  common ancestor w/ bears than raccoons
• DNA places red pandas outside bear clade in
  different clade that includes raccoons, seals,
  weasels

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Mystery Clue

• Page 522
• DNA comparisons show that some populations of
  brown bears are more closely related to polar
  bears than they are to other brown bears.
• What do you think this means for the
  classification of polar bears?

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Section 18.3Building the Tree of Life

• Objectives
• What are the six kingdoms of life as they are now
  identified?
• What does the tree of life show?
• Define
• Domain
• Bacteria
• Archea
• Eukarya

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I. Changing Ideas About Kingdoms

• Linnaeus time only differences among living
  things were fundamental chars that separated
  animals from plants
• Animals orgs that moved from place to place and
  used food for energy
• Plants green orgs that generally did not move
  and got energy from sun
• Problem Linnaeuss 2 kingdoms did not reflect
  full diversity of life so classification system
  changed dramatically and still changing

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A. Five Kingdoms

• Single celled microorganisms significantly
  different from plants and animals
• At first ? all placed in one kingdom (Protista)
• Then ? yeasts, molds, mushrooms (Fungi)
• Later ? bacteria (no nuclei, mitochondria,
  chloroplasts prokaryotes (Monera)
• Single-celled eukaryotic orgs remained in
  Protista
• 5 Kingdoms Monera, Protista, Fungi, Plantae,
  Animalia

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B. Six Kingdoms

• 1990s researchers learned a great deal about
  genetics and biochemistry of bacteria
• Orgs in Monera 2 genetically and biochemically
  different groups (Eubacteria Archaebacteria)
• The six-kingdom system of classification includes
  the kingdoms Eubacteria, Archaebacteria,
  Protista, Fungi, Plantae, and Animalia

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C. Three Domains

• Genomic analysis revealed that 2 main prokaryotic
  groups are ever more different from each other
  and from eukaryotes than previously thought ? new
  taxonomic category (domain)
• Domain larger, more inclusive category than
  kingdom
• 3 domains Bacteria (kingdom Eubacteria),
  Archaea (kingdom Archaebacteria), Eukarya
  (kingdoms Fungi, Planta, Animalia, Protista)
• Protista paraphyletic group not a true
  clade
• no way to put all unicellular eukaryotes into
  clade that contains single common ancestor, all
  of its descendants, and only those descendants

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II. The Tree of All Life

• Goal present all life on single evolutionary
  tree
• Relationships studied ? grouping changes names
  of groups change
• Cladograms visual presentations of hypotheses
  about relationships (not hard and fast facts)
• The tree of life shoes current hypotheses
  regarding evolutionary relationships among the
  taxa within the three domains of life

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A. Domain Bacteria

• Unicellular
• Prokaryotic
• Cells have thick, rigid walls that surround cell
  membrane
• Cell walls contain peptidoglycan
• Some photosynthesize and others dont
• Some need oxygen to survive and others are killed
  by oxygen
• Corresponds to kingdom Eubacteria

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B. Domain Archaea

• Unicellular
• Prokaryotic
• Live in some of most extreme environments
  (volcanic hot springs, brine pools, black organic
  mud)
• Many can survive only in absence of oxygen
• Cell walls lack peptidoglycan
• Cell membranes contain unusual lipids that are
  not found in any other orgs
• Corresponds to kingdom Archaebacteria

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C. Domain Eukarya

• Consists of all orgs that have nucleus
• 4 major groups Protista, Fungi, Plantae,
  Animalia

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The Protists Unicellular Eukaryotes

• Paraphyletic group
• Current cladistic analysis divides into at least
  5 clades
• Each group of eukaryotes formerly known as
  protists is separate each shares closest
  common ancestor with other groups rather than
  with each other.
• Most unicellular
• 1 group brown algae multicellular
• Some photosynthetic others heterotrophic
• Some display characters that most closely
  resemble those of plants, fungi, or animals

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2. Fungi

• Heterotrophs
• Cell walls containing chitin
• Feed on dead or decaying organic material
• Secrete digestive enzymes into food ? breaks down
  into smaller molecules ? absorb small molecules
  into bodies
• Some multicellular (mushrooms)
• Some unicellular (yeasts)

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3. Plantae

• Autotrophs
• Cell walls contain cellulose
• Conduct photosynthesis using chlorophyll
• Sister group to red algae (protists)
• Includes green algae, mosses, ferns, cone-bearing
  plants flowering plants

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4. Animalia

• Multicellular
• Heterotrophic
• No cell walls
• Most can move about (some for only part of life
  cycle)
• Incredible diversity
• Many species of animals exist in nearly every
  part of planet

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Solve the Chapter Mystery

• Page 533
• List the evidence that supports classifying polar
  bears and brown bears into two different species.
  Then list the evidence that indicates that polar
  bears and brown bears belong to the same species
• What evidence indicates that different
  populations of brown bears belong to different
  clades?
• Do you think that the classic definition of
  species a group of similar organisms that can
  breed and produce fertile offspring is still
  adequate? Why or why not?