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Phylogeny and Systematics

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Phylogeny and Systematics Chapter 10 * * * * * * * * * * * * * * * * * * * * * * * * * * * * Taxonomy A theory of taxonomy allows us to rank taxonomic groups. – PowerPoint PPT presentation

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Title: Phylogeny and Systematics


1
Phylogeny and Systematics
  • Chapter 10

2
Taxonomy
  • Taxonomy produces a formal system for naming and
    classifying species to illustrate their
    evolutionary relationship.

3
Taxonomy Systematics
  • Taxonomy
  • Formal system for naming and classifying species.
  • Systematics
  • Broader science of classifying organisms based on
    similarity, biogeography, etc.
  • Systematic zoologists have three goals
  • To discover all species of animals.
  • To reconstruct their evolutionary relationships.
  • To classify animals according to their
    evolutionary relationships.

4
Taxonomy
  • Introduction of evolutionary theory into animal
    taxonomy changed taxonomists role from one of
    classification to systematization.
  • Classification denotes the construction of
    classes.
  • Grouping of organisms that possess a common
    feature called an essence used to define the
    class.

5
Taxonomy
  • Systematization places groups of species into
    units of common evolutionary descent.
  • Character variation is used to diagnose systems
    of common descent.
  • No requirement that an essential character be
    maintained throughout the system for its
    recognition as a taxon.

6
Taxonomy
  • In classification
  • Taxonomist asks whether a species being
    classified contains the defining feature of a
    particular taxonomic class.
  • In systematization
  • Taxonomist asks whether the characteristics of a
    species confirm or reject the hypothesis that it
    descends from the most recent common ancestor of
    a particular taxon.

7
Linnaeus and Classification
  • Carolus Linnaeus designed our hierarchical
    classification scheme.
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species

8
Linnaeus and Classification
  • All animals are placed in Kingdom Animalia.
  • Names of animal groups at each rank in the
    hierarchy are called taxa (taxon).
  • Each rank can be subdivided into additional
    levels of taxa.
  • Superclass, suborder, etc.

9
Linnaeus and Classification
10
Linnaeus and Classification
  • Binomial nomenclature is the system Linnaeus used
    for naming species.
  • Genus and species
  • Names are latinized and italicized, only the
    genus is capatilized.
  • Sitta carolinensis

11
Linnaeus and Classification
  • A trinomial name includes a subspecies epithet.
  • Ensatina escholtzii escholtzii
  • E. e. klauberi

12
Species
  • Defining a species can be difficult.
  • Criteria
  • Common descent
  • The smallest distinct groupings of organisms
    sharing a pattern of descent.
  • Morphological molecular techniques
  • Members of a species must form a reproductive
    community that excludes other species.

13
Species
  • The geographic range of a species is its
    distribution in space.
  • Evolutionary duration of a species is its
    distribution in time.
  • A worldwide species is cosmopolitan.
  • One with a very localized range is called endemic.

14
Typological Species Concept
  • The typological or morphological species concept
    relies on type specimens that represent the ideal
    form for the species. When trying to name a
    specimen, the type specimens were compared.
  • Scientists still name species by designating a
    type specimen.

15
The Biological Species Concept
  • The biological species concept emerged during the
    evolutionary synthesis.
  • A species is a reproductive community of
    populations (reproductively isolated from others)
    that occupies a specific niche in nature. Mayr
    1982
  • Sibling species fit this category, but can only
    be differentiated with molecular techniques.
  • Lacks a temporal dimension.
  • Degree of reproductive isolation necessary?
  • Species that reproduce asexually?

16
Evolutionary Species Concept
  • The evolutionary species concept states that a
    single lineage of ancestor-descendant populations
    that maintains its identity from other such
    lineages and that has its own evolutionary
    tendencies and historical fate.
  • Definition accommodates both sexual and asexual
    forms as well as fossils.

17
Phylogenetic Species Concept
  • The phylogenetic species concept is defined as an
    irreducible (basal) grouping of organisms
    diagnosably distinct from other such groupings
    and within which there is a parental pattern of
    ancestry and descent.
  • Both asexual and sexual groups are covered.

18
Phylogenetic Species Concept
  • Main difference in practice between the
    evolutionary and phylogenetic species concepts
  • The latter emphasizes recognizing as separate
    species the smallest groupings of organisms that
    have undergone independent evolutionary change.
  • Discerns the greatest number of species but may
    be impractical.
  • Disregards details of evolutionary process.

19
Investigating the Tree of Life
  • A major goal of systematics is to infer the
    evolutionary tree or phylogeny the evolutionary
    history of a species or group of related species.

20
Phylogeny
  • Phylogenies are inferred by identifying
    organismal features, characters, that vary among
    species.
  • Morphological
  • Chromosomal
  • Molecular
  • Behavioral or ecological

21
Phylogeny
  • Shared characters that result from common
    ancestry are homologous.
  • Independent evolution of similar characters that
    are NOT homologous is called homoplasy.

22
Sorting Homology from Analogy
  • A potential misconception in constructing a
    phylogeny is similarity due to convergent
    evolution, called analogy, rather than shared
    ancestry.

23
Sorting Homology from Analogy
  • Convergent evolution occurs when similar
    environmental pressures and natural selection
    produce similar (analogous) adaptations in
    organisms from different evolutionary lineages.

24
Sorting Homology from Analogy
  • Analogous structures or molecular sequences that
    evolved independently are also called
    homoplasies.

25
Shared Primitive and Shared Derived
Characteristics
  • A shared primitive (ancestral) character
  • Is a homologous structure that predates the
    branching of a particular clade from other
    members of that clade.
  • Is shared beyond the taxon we are trying to
    define.
  • Example mammals all have a backbone, but so do
    other vertebrates.

26
Shared Primitive and Shared Derived
Characteristics
  • A shared derived character is an evolutionary
    novelty unique to a particular clade.
  • All mammals have hair, and no other animals have
    hair.

27
Phylogeny
  • The form of the character that was present in the
    common ancestor of the entire group is called
    ancestral.
  • Variant forms of the character arose later and
    are called derived character states.
  • Determining polarity of a character involves
    determining which state is ancestral.

28
Phylogeny
  • Polarity is determined by using outgroup
    comparison.
  • An outgroup is closely related, but not part of
    the group being examined (the ingroup).
  • If a character is found in both the study group
    and the outgroup, it is considered ancestral for
    the study group.
  • Character groups found in the study groups but
    not the outgroups are derived.

29
Phylogeny
  • Clades are organisms or species that share
    derived character states and form a subset within
    a larger group.
  • A synapomorphy is a derived character shared by
    the members of the clade.
  • A clade corresponds to a unit of evolutionary
    common descent.
  • A nested hierarchy is formed by the derived
    states of all characters in a study group.

30
Phylogeny
  • Ancestral character states for a taxon are called
    plesiomorphic.
  • Sharing these ancestral characters is called
    symplesiomorphy.
  • Symplesiomorphies, unlike synapomorphies, do not
    provide information on nesting of clades groups
    with derived characters get left out.

31
Phylogeny
  • The nested hierarchy of clades can be represented
    as a cladogram that is based on shared
    synapomorphies.

32
Phylogeny
  • A phylogenetic tree is another way of
    representing evolutionary relationships.
  • Branches represent real lineages that occurred in
    the evolutionary past.
  • Includes information about ancestors, duration of
    evolutionary lineages, amounts of evolutionary
    change that has occurred.

33
Sources of Phylogenetic Information
  • Characters used to construct cladograms can be
    found using
  • Comparative morphology examine shapes and sizes
    of organismal structures, including developmental
    origins.
  • Comparative biochemistry examine sequences of
    amino acids and nucleotides to identify variable
    characters.
  • Comparative cytology uses variation in numbers,
    shapes, and sizes of chromosomes and their parts.

34
Taxonomy
  • A theory of taxonomy allows us to rank taxonomic
    groups.
  • Two popular theories
  • Evolutionary taxonomy
  • Phylogenetic systematics
  • Both based on evolutionary principles, sometimes
    results conflict.

35
Cladistics
  • A valid clade is monophyletic.
  • Signifying that it consists of the ancestor
    species and all its descendants.

36
Cladistics
  • A paraphyletic clade is a grouping that consists
    of an ancestral species and some, but not all, of
    the descendants.

37
Cladistics
  • A polyphyletic grouping includes numerous types
    of organisms that lack a common ancestor.

38
Traditional Evolutionary Taxonomy
  • Evolutionary taxonomy utilizes common descent and
    the amount of adaptive evolutionary change to
    rank higher taxa.
  • Sometimes this type of classification includes
    paraphyletic groupings.

39
Phylogenetic Systematics
  • Phylogenetic systematics, or cladistics,
    emphasizes common descent and is based on
    cladograms.
  • All taxa must be monophyletic.
  • Cladistic taxonomists have moved chimpanzees,
    gorillas, and orangutans into the family
    Hominidae with humans.
  • Humans and chimps form a sister group, as do the
    human/chimp group and gorillas.

40
Theories of Taxonomy
  • Both evolutionary and cladistic taxonomy
  • Accept monophyletic groups.
  • Reject polyphyletic groups.
  • Differ on accepting paraphyletic groups.
  • Traditional evolutionary taxonomy does.
  • Phylogenetic systematics does not.
  • Difference has important evolutionary
    implications.

41
Theories of Taxonomy
  • Current State of Animal Taxonomy
  • Modern animal taxonomy was established using
    evolutionary systematics and recent cladistic
    revisions.
  • PhyloCode
  • New taxonomic system
  • Being developed as an alternative to Linnean
    taxonomy.
  • Replaces Linnean ranks with codes that denote the
    nested hierarchy of monophyletic groups conveyed
    by cladograms.
  • The terms primitive, advanced, specialized
    and generalized are used for specific
    characteristics and not for groups as a whole.

42
Maximum Parsimony and Maximum Likelihood
  • Systematists can never be sure of finding the
    single best tree in a large data set.
  • Narrow the possibilities by applying the
    principles of maximum parsimony and maximum
    likelihood.

43
Parsimony
  • Among phylogenetic hypotheses the most
    parsimonious tree is the one that requires the
    fewest evolutionary events to have occurred in
    the form of shared derived characters.
  • Occams Razor

44
Parsimony
  • The principle of maximum likelihood states that,
    given certain rules about how DNA changes over
    time, a tree can be found that reflects the most
    likely sequence of evolutionary events.

45
Phylogenetic Trees as Hypotheses
  • The best hypotheses for phylogenetic trees are
    those that fit the most data morphological,
    molecular, and fossil.

46
Molecular Systematics
  • Much of an organisms evolutionary history is
    documented in its genome.
  • Comparing nucleic acids or other molecules to
    infer relatedness is a valuable tool for tracing
    organisms evolutionary history.

47
Major Divisions of Life
  • Aristotles two kingdom system included plants
    and animals.
  • One-celled organisms became a problem
  • Haeckel (1866) proposed Protista for
    single-celled organisms.
  • R.H. Whittaker (1969) proposed a five-kingdom
    system to distinguish prokaryotes and fungi.

48
Major Divisions of Life
  • Woese, Kandler and Wheelis (1990) proposed three
    monophyletic domains above kingdom levelEucarya,
    Bacteria and Archaeabased on ribosomal RNA
    sequences.

49
Major Division of Life
  • More revisions are necessary to clarify taxonomic
    kingdoms based on monophyly.
  • Protozoa
  • Neither animals nor a valid monophyletic taxon.
  • Protista
  • Not a monophyletic kingdom.
  • Most likely composed of seven or more kingdoms.

50
Major Subdivisions of the Animal Kingdom
  • Traditional groupings based on embryological and
    anatomical characters
  • Branch A (Mesozoa) phylum Mesozoa,
    the mesozoa
  • Branch B (Parazoa) phylum Porifera,
    the sponges and phylum Placozoa
  • Branch C (Eumetazoa) all other phyla

51
Major Subdivisions of the Animal Kingdom
  • Branch C (Eumetazoa) all other phyla
  • Grade I (Radiata) phyla Cnidaria, Ctenophora
  • Grade II (Bilateria) all other phyla
  • Division A (Protostomia) Protostome
    characteristics
  • Acoelomates phyla Platyhelminthes,
    Gnathostomulida, Nemertea
  • Pseudocoelomates phyla Rotifera, Gastrotricha,
    Kinorhyncha, Nematoda, Nematomorpha,
    Acanthocephala, Entoprocta, Priapulida,
    Loricifera
  • Eucoelomates phyla Mollusca, Annelida,
    Arthropoda, Echiurida, Sipunculida, Tardigrada,
    Onychophora.

52
Major Subdivisions of the Animal Kingdom
  • Division B (Deuterostomia) Deuterostome
    characteristics
  • phyla Phoronida, Ectoprocta, Chaetognatha,
    Brachiopoda, Echinodermata, Hemichordata, Chordata

53
Major Subdivisions of the Animal Kingdom
  • Recent molecular phylogenetic studies have
    challenged traditional classification of
    Bilateria.
  • Grade II Bilateria
  • Division A (Protostomia)
  • Lophotrochozoa phyla platyhelminthes, Nemertea,
    Rotifera, Gastrotricha, Acanthocephala, Mollusca,
    Annelida, Echiurida, Sipunculida, Phoronida,
    Ectoprocta, Entoprocta, Gnathostomulida,
    Chaetognatha, Brachiopoda
  • Ecdysozoa phyla Kinorhyncha, Nematoda,
    Nematomorpha, Priapulida, Arthropoda, Tardigrada,
    Onychophora, Loricifera
  • Division B (Deuterostomia)
  • phyla Chordata, Hemichordata, Echinodermata

54
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