A1260002745DGsLm

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Systematics and the Phylogenetic
Revolution Chapter 23
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• Introduction
• All organisms
• Are composed of one or more cells
• Carry out metabolism
• Transfer energy with ATP
• Encode hereditary information in DNA
• Tremendous diversity of life
• Bacteria-----whales----sequoia trees
• Biologists group organisms based on shared
  characteristics

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Systematics

• Since fossil records are not complete, scientists
  rely on other types of evidence to establish the
  best hypothesis of evolutionary relationships
• Systematics what to consider when making a
  phylogeny
• Phylogeny a hypothesis about patterns of
  relationship among species.

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Systematics

• Darwin envisioned that all species were descended
  from a single common ancestor
• He depicted this history of life as a branching
  tree.
• Now called a cladogram

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Systematics

• Twigs of a tree represent existing species
• Joining of twigs and branches reflects the
  pattern of common ancestry back in time to a
  single common ancestor
• Darwin called this process descent with
  modification

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Systematics

• Phylogenies depict evolutionary relationships

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Systematics

• Oscillating selection Traits can evolve in one
  direction, then back the other way
• Evolution is not always divergent convergent
  evolution
• Use similar habitats
• Similar environmental pressures
• Evolutionary reversal process in which a
  species re-evolves the characteristics of an
  ancestral species

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Cladistics

• Derived characteristic similarity that is
  inherited from the most recent common ancestor of
  an entire group
• Ancestral similarity that arose prior to the
  common ancestor of the group
• In cladistics, only shared derived characters are
  considered informative about evolutionary
  relationships
• To use the cladistic method character variation
  must be identified as ancestral or derived

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Cladistics

• Characters can be any aspect of the phenotype
• Morphology - Physiology
• Behavior - DNA
• Characters should exist in recognizable character
  states
• Example Teeth in amniote vertebrates has two
  states, present in most mammals and reptiles and
  absence in birds and turtles

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Cladistics

• Examples of ancestral versus derived characters
• Presence of hair is a shared derived feature of
  mammals
• Presence of lungs in mammals is an ancestral
  feature also present in amphibians and reptiles

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Cladistics

• Determination of ancestral versus derived
• First step in a manual cladistic analysis is to
  polarize the characters (are they ancestral or
  derived)
• Example polarize teeth means to determine
  presence or absence in the most recent common
  ancestor

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Cladistics

• Outgroup comparison is used to assign character
  polarity
• A species or group of species not a member of the
  group under study is designated as the outgroup
• Outgroup species do not always exhibit the
  ancestral condition

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Cladistics

• When the group under study exhibits multiple
  character states, and one of those states is
  exhibited by the outgroup, then that state is
  ancestral and other states are derived
• Most reliable if character state is exhibited by
  several different outgroups

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Cladistics

• Following the character state-outgroup method
• Presence of teeth in mammals and reptiles is
  ancestral
• Absence of teeth in birds and turtles is derived

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Cladistics

• Construction of a cladogram
• Polarize characteristics
• Clade species that share a common ancestor as
  indicated by the possession of shared derived
  characters
• Clades are evolutionary units and refer to a
  common ancestor and all descendants
• Synapomorphy a derived character shared by
  clade members

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Cladistics

• A simple cladogram is a nested set of clades
• Plesiomorphies ancestral states
• Symplesiomorphies shared ancestral states (like
  having a tail)

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Cladistics
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Cladistics

• Homoplasy a shared character state that has not
  been inherited from a common ancestor
• Results from convergent evolution
• Results from evolutionary reversal
• If there are conflicts among characters, use the
  principle of parsimony which favors the
  hypothesis that requires the fewest assumptions

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Cladistics

• Parsimony and Homoplasy
• Gorilla has a homoplasmic state relative to a frog

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Other Phylogenetic Methods

• Rate at which some parts of the DNA genome evolve
• Mutations in repetition sequences, not deleted by
  natural selection
• Statistical approaches
• Molecular clock rate of evolution of a molecule
  is constant through time

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Systematics and Classification

• Classification how we place species and higher
  groups into the taxonomic hierarchy
• Genus, family, class..
• Paraphyletic group includes the most recent
  common ancestor of the group, but not all its
  descendants

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Systematics and Classification

• Monophyletic group includes the most recent
  common ancestor of the group and all of its
  descendants (clade)

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Systematics and Classification

• Paraphyletic group includes the most recent
  common ancestor of the group, but not all its
  descendants

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Systematics and Classification

• Polyphyletic group does not include the most
  recent common ancestor of all members of the
  group (OR see it like adding an extra species in
  the group that doesnt belong there)

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Systematics and Classification

• Phylogenetic species concept (PSC)
• Focuses on shared derived characters
• Biological species concept (BSC)
• Defines species as groups of interbreeding
  population that are reproductively isolated
• Phylogenetic species concept species should be
  applied to groups of populations that have been
  evolving independently of other groups

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Comparative Biology

• Phylogenetics is the basis of all comparative
  biology
• Homologous structures are derived from the same
  ancestral source (e.g. dolphin flipper and horse
  leg)
• -Parental care
• Dinosaurs, birds, crocodiles
• Homologous behavior
• Homoplastic structures are not (e.g. wings of
  birds and dragonflies)

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Comparative Biology

• Parental care in dinosaurs and crocodiles

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Comparative Biology

• Most complex characters evolve through a sequence
  of evolutionary changes
• Modern-day birds
• wings, feathers, light bones, breastbone
• Initial stages of a character evolved as an
  adaptation to some environmental selective
  pressure
• First featherlike structure evolved in theropod
  phylogeny
• Insulation or perhaps decoration

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Comparative Biology
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Comparative Biology

• Phylogenetics helps explain species
  diversification
• Use phylogenetic analysis to suggest and test
  hypotheses
• Species richness in beetles
• Coleoptera 60 of all animals are insects and
  80 of all insects are beetles
• Phytophaga clade with most herbivorous beetles
• Family Nemonychidae specialized on conifers
  since Jurassic

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Comparative Biology

• Evolutionary diversification of the
  Phytophaga...compare of descendant species that
  fed on angiosperm versus conifer or cycad

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Comparative Biology

• Phylogenetic explanations for beetle
  diversification
• Not the evolution of herbivory
• Specialization on angiosperms a prerequisite for
  diversification
• Risen 5 times independently within herbivorous
  beetles
• Angiosperm specializing clade is more
  species-rich than the clade most closely related