Speciation and Patterns of Evolution

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Speciation and Patterns of Evolution

• Macroevolution the origin of new taxonomic
  groups

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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.)

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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.

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Figure 24.1 Two patterns of speciation
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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

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Figure 24.1 Two patterns of speciation
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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

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Figure 24.2a The biological species concept is
based on interfertility rather than physical
similarity
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Figure 24.2b The biological species concept is
based on interfertility rather than physical
similarity
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Figure 24.3 Courtship ritual as a behavioral
barrier between species
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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

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Figure 24.5 A summary of reproductive barriers
between closely related species
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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)

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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

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• 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

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• 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)

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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

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Figure 24.6 Two modes of speciation
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Figure 24.7 Allopatric speciation of squirrels
in the Grand Canyon
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Figure 24.8 Has speciation occurred during
geographic isolation?
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Figure 24.9 Ensatina eschscholtzii, a ring
species
Allopatric speciation in progress????
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Figure 24.10 Long-distance dispersal
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Figure 24.11 A model for adaptive radiation on
island chains
See page 471
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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)

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Fruit Fly examples pre and postzygotic barriers
(pages 471-473)
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Figure 24.12 Evolution of reproductive isolation
in lab populations of Drosophila
Diane Dodd Yale University
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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

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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)

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

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Figure 24.16 Mate choice in two species of Lake
Victoria cichlids
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Figure 24.15 One mechanism for allopolyploid
speciation in plants
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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

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