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Speciation and Patterns of Evolution

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Title: Speciation and Patterns of Evolution


1
Speciation and Patterns of Evolution
  • Macroevolution the origin of new taxonomic
    groups

2
SpeciesLatin for kind
  • Group of natural pops whose members can
    interbreed with one another but cannot (or do
    not) interbreed with members of other such groups
  • Species can stay separate when have GENETIC
    ISOLATION in place (otherwise, would lose unique
    characteristics that set them apart.)

3
Speciation
  • Definition
  • When splinter groups, reproductively isolated
    from the population as a whole, undergo
    sufficient change that can become new species.
  • Changes in allele frequencies that are
    significant enough to mark the formation of a new
    species (a daughter species from a parent
    species.)
  • Speciation is NOT the same thing as Natural
    Selection speciation could be a potential
    consequence of natural selection or any other
    processes working with N.S.

4
Figure 24.1 Two patterns of speciation
5
2 patterns of speciation
  • Anagenesis accumulation of heritable changes in
    a population, transforming the pop into a new
    species
  • Cladogenesis branching evolution new species
    arise from a population that buds from a parent
    species basis for biological diversity

6
Figure 24.1 Two patterns of speciation
7
Species Concepts.
  • Biological Species Concept
  • defines a species as a pop or group of pops
    whose members have the potential to interbreed
    with one another in nature to produce fertile
    offspring but who cannot produce fertile
    offspring with members of other species
  • hinges on reproductive isolation and
    interfertility
  • each species isolated by barriers that prevent
    interbreeding

8
Figure 24.2a The biological species concept is
based on interfertility rather than physical
similarity
9
Figure 24.2b The biological species concept is
based on interfertility rather than physical
similarity
10
Figure 24.3 Courtship ritual as a behavioral
barrier between species
11
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12
Prezygotic and Postzygotic barriers pages 466-467
  • Pre -habitat isolation
  • -behavioral isolation
  • -temporal isolation
  • -mechanical isolation
  • -gametic isolation
  • Post -reduced hybrid viability
  • -reduced hybrid fertility
  • -hybrid breakdown

13
Figure 24.5 A summary of reproductive barriers
between closely related species
14
Limitations to BSC
  • Does not work in all situations
  • Impractical for demarcating species in most cases
  • cant tell what happened with fossils
  • Dont know enough about even current animals
    in wild to determine if wont mate or cant
    mate
  • No info on asexual orgs (classified based on
    structure and biochemistry, not mating)

15
Alternative concepts of species
  • Ecological Species Concept
  • defines a species in terms of its ecological
    niche, the set of environmental resources a
    species uses.
  • Ex. Parasite defined by adaptations to a
    specific host (does accommodate asexual orgs.)
  • Pluralistic Species Concept
  • here, the factors that are most important for
    the cohesion of individuals as a species varies
    (takes into account more possibilities)
  • Ex. Reproductive isolation, adaptation to niche,
    combo

16
  • These first 3 are explanatory concepts WHY are
    different species
  • 2 more approaches are focused more on how to
    identify and how are related historically

17
  • Morphological Species Concept
  • characterizes species in terms of unique
    structural features (not why, but what and how)
  • Genealogical Species Concept
  • defines a species as a set of organisms with a
    unique genetic history (ids species, not why)

18
Modes of Speciation
  • Allopatric takes place in a pop with
    geographically separate ranges
  • Sympatric new species arise within the range of
    parent populations rather than in geographically
    separate pops

19
Figure 24.6 Two modes of speciation
20
Figure 24.7 Allopatric speciation of squirrels
in the Grand Canyon
21
Figure 24.8 Has speciation occurred during
geographic isolation?
22
Figure 24.9 Ensatina eschscholtzii, a ring
species
Allopatric speciation in progress????
23
Figure 24.10 Long-distance dispersal
24
Figure 24.11 A model for adaptive radiation on
island chains
See page 471
25
Potential misunderstandings
  • Geographical isolation does not REALLY qualify as
    reproductive isolation in the biological sense.
  • -Also need reproductive barriers
  • Speciation is not due to some drive to erect
    potential reproductive barriers usually
    coincidental due to gene pool changes (natural
    selection and genetic drift are examples)

26
Fruit Fly examples pre and postzygotic barriers
(pages 471-473)
27
Figure 24.12 Evolution of reproductive isolation
in lab populations of Drosophila
Diane Dodd Yale University
28
Wrapping up allopatric speciation
  • New species forms while geographically isolated
    from it ancestor
  • As genetic drift and natural selection take place
    in this new groups gene pool, reproductive
    isolation occurs AS A BY-PRODUCT of the genetic
    change

29
Sympatric speciation
  • New species arise within the range of parent
    populations rather than in geographically
    separate populations
  • Ex.
  • Polyploid speciation in plants
  • see page 473,
  • autopolyploid primroses
  • allopolyploid hybrids (goatsbeard weed)

30
Figure 24.14b The new primrose species of
botanist Hugo de Vries
31
Figure 24.13 Sympatric speciation by
autopolyploidy in plants
32
  • Polyploid speciation in animals
  • Less common than in plants, but does occur
  • Ex.
  • Wasps that pollinate figs
  • Cichlids (fish)

33
Figure 24.16 Mate choice in two species of Lake
Victoria cichlids
34
Figure 24.15 One mechanism for allopolyploid
speciation in plants
35
Patterns of Evolution
  • Mass Extinctions
  • Adaptive Radiation small group of species
    evolved into several different forms
  • Convergent evolution unrelated orgs look
    similar because of similarity in environments
  • Coevolution process by which two species evolve
    in response to each other over time
  • Ex. Flowers and insects that pollinate
  • Punctuated Equilibrium long stable periods of
    no changes followed by brief periods of rapid
    change
  • Gradualism slow, minute changes that build up
    over time

36
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37
Figure 24.18 A range of eye complexity among
mollusks
Exaptations -- page 477
38
Figure 24.19 Allometric growth
Allometric growth page 478
39
Figure 24.20 Heterochrony and the evolution of
salamander feet among closely related species
Heterochrony page 478-479
40
Figure 24.21 Paedomorphosis
Paedomorphosis page 479
41
Figure 24.22 Hox genes and the evolution of
tetrapod limbs
Homeotic genes page 479
42
Figure 24.23 Hox mutations and the origin of
vertebrates
43
Figure 24.24 The branched evolution of horses
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