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The Origin of Species

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					The Origin of
Species
Chapter 24
Basic Patterns of Evolution
 Anagenesis  one species accumulates
  heritable changes, gradually the species
  becomes a different species
 Cladogenesis  branching evolution, one
  species to several w/ potential for
  interbreeding
Biological Concept of Species

   A population or group of populations
    whose members have the potential to
    interbreed with each other in nature to
    produce viable, fertile offspring, but
    who cannot produce viable, fertile
    offspring with members of other
    species
Species are based on interfertility, not
physical similarity

   The eastern and western meadowlarks may
    have similar shapes and coloration, but
    differences in song help prevent interbreeding
    between the two species
Humans have considerable diversity,
but we all belong to the same species because
of our capacity to interbreed
How are Species kept separate?
 Reproductive Barriers  prevents
  populations belonging to different
  species from interbreeding, even if
  their ranges overlap
 Reproductive barriers
     prezygotic
     postzygotic,
Pre zygotic Barriers
   Impede mating between species or
    hinder fertilization of ova if members
    of different species attempt to mate
     Habitat isolation
     Behavioral Isolation
     Temporal Isolation
     Mechanical Isolation
     Gametic isolation
Post zygotic Barriers
   Prevents the hybrid zygote from
    developing into a viable, fertile adult
     Reduced hybrid viability
     Reduced hybrid fertility
     Hybrid breakdown
Habitat Isolation
   Two organisms that use different
    habitats even in the same geographic
    area are unlikely to encounter each
    other to even attempt mating
     Two  species of garter snakes, in the genus
      Thamnophis, that occur in the same areas
      but because one lives mainly in water and
      the other is primarily terrestrial, they
      rarely encounter each other.
Behavioral Isolation
   Many species use elaborate behaviors
    unique to a species to attract mates
   Visual Fireflies
     Bird plumage
     Red Stickleback
     Fiddler Crabs
     Fruit Fly
     Blue Footed Booby
   OlfactoryScandinavian
    mothPheromones
   Auditory: Bird songs, frog calls
    Temporal Isolation
    Two species that
     breed during              Wood frog 44o
     different times of
     day, different            Leopard     55o
     seasons, or               Frogs
     different years           Green       60o
     cannot mix gametes        Frog
       Flowers
                               Bull Frog   Above 60o
       Skunk mating seasons
       Frogs
Mechanical Isolation
   Closely related species may attempt to
    mate but fail because they are
    anatomically incompatible and transfer
    of sperm is not possible
     Flower structure of certain flowering
      plants prevents pollination by insects or
      other animals
     With many insects the male and female
      copulatory organs of closely related
      species do not fit together, preventing
      sperm transfer
Gametic Isolation
   Gametes of two species do not form a
    zygote because of incompatibilities
    preventing fusion or other mechanisms
     Sperm/egg recognition
     Reproductive Tract unfavorable
Post Zygotic Barriers
   Reduced hybrid
    viability
     Hybrids may be
      frailhybrids
      between frogs in the
      genus Rana, which do
      not complete
      development and
      those that do are
      frail.
    Reduced Hybrid Fertility
   Hybrids may be vigorous but may be infertile and
    the hybrid cannot backbreed with either
    parental species
   Horse (2n = 64)
   Donkey (2n = 62)
Reduced Hybrid Fertility

 Mule (which is
  sterile)
 Hence, donkeys and
  horses are separate
  species
Hybrid Breakdown

   Some first
    generation
    hybrids are viable
    and fertile, but
    when the mate
    with one another,
    offspring are
    feeble
Species Concept
   Biological Concept“Species are groups of
    actually or potentially interbreeding natural
    populations, which are reproductively isolated
    from other such groups.” Ernst Mayr.
   Morphological species concept, the oldest and
    still most practical, defines a species by a
    unique set of structural features
   Ecological species defines a species in terms
    of its ecological niche, the set of
    environmental resources that a species uses
    and its role in a biological community
Biogeography of Species
   Two ways in which
    speciation can
    occur.
     Allopatric
      speciation occurs
      when a gene pool is
      divided into two
     Sympatric
      speciation occurs
      without geographic
      separation
Allopatric Speciation
   A geographic barrier isolates the
    population and species are maintained
     Squirrels   on the N/S of the Grand Canyon
Allopatric speciation of squirrels in the
Grand Canyon
Sympatric Speciation
   Reproductive isolation without
    geographic isolation
     Autopoliploidy
     Allopolyploidy
     Non-random   mating animals
Autopoliploidy
   Single parent doubles chromosome #
   Results in TETRAPLOIDS
Allopolyploidy
   2 different species are involvedpolyploid
    hybrid is formed
   This is how modern wheat, oats, cotton,
    potatoes were developed
   More important in plant evolution
Non-random mating animals

   Mate choice is based
    on coloration
 Adaptive Radiation
Evolution of many diversely adapted species from a
  common ancestor upon introduction of new
  environmental opportunities
Tempo of Speciation
   Niles
    Eldredge/Steven J.
    Gould
   Punctuated
    Equilibrium
   Gradualism
Macroevolution

 Leads to new taxonomic groups
 Origin of mammals from reptiles
 Feathers and flight
 Increasing brain size of mammals
 Adaptive radiation of flowering plants
Macroevolution
 Evolutionary novelties are modified versions of older
  structures
Exaptations: Preadaptations
        structures that evolve in one context but become co-opted
        for another
Ex. Ancestral reptiles
     Hollow bones in birds

‘Evolution is like modifying a machine while it is running!’
Evo-Devo
   The role evolution has in development
     Ex:  Shape of an organism depends on
      relative growth rate of its parts
   Changes in Rate and Timing
               Growth
     Allometric
     Heterochrony
     Paedomorphosis

   Changes in Spatial Patterns
     Homeotic   Genes
   Differential growth rate expanded
    time of brain development
Figure 24.19 Allometric growth

  Allometric growth: proportional change
  Heterochrony




Longer time for foot growth         Foot growth ends sooner-
results in longer digits and less   shorter digits and more
webbing                             webbing
Paedomorphosis
   Juvenile traits extended to adult
   Salamanders that retain gills don’t have to
    leave the water
Homeotic Genes

 Control the 3D placement of structures
 HOX gene organize the embryo in
  space
 Invertebrates 1 set
 Vertebrates several sets more
  complex growth

				
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posted:5/9/2013
language:English
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