Speciation

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Speciation
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Speciation is the process of one species
diverging (evolving) into two (or more) species.
At the most basic level, the process is
dictated by two processes1) Gene flow 2)
Selection
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• Gene flow is the movement of genetic material
  within, and among, populations of a given species
  
• For (most) animals this involves the movement of
  individuals (offspring, mostly) over geographic
  distances. For gene flow to be accomplished that
  individual would then reproduce.

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Hit the road jack!!
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• Gene flow is the movement of genetic material
  within, and among, populations of a given species
  
• For (most) animals this involves the movement of
  individuals (offspring, mostly) over geographic
  distances. For gene flow to be accomplished,
  then, that individual would then reproduce.
• In plants, gene flow is accomplished through
  pollen movement, and through seed (or clone)
  dispersal.

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Populations of Populus nigra.
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Gene flow binds together the populations that
make up a species.
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Speciation is the process of one species
diverging (evolving) into two (or more) species.
At the most basic level, the process is
dictated by two processes1) Gene flow 2)
Selection
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2) (Natural) Selection is the differential
success of individuals within a population such
that traits are eliminated or emphasized over
(evolutionary) time.- variation among
individuals in a heritable trait.- variation
results in difference in reproductive
success/survival.
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Flowering dogwood (Cornus florida)
http//www.plantbio.ohiou.edu/trees/Cornus20flori
da.htm
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Role of Selection? (eg. habitats different)
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Selection is driving the populations apart.
Gene flow is holding the populations together.
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what if gene flow is prevented?
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Differentiation, the development of ecotypes...
maybe, later, speciation
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Okso how do you get from here, to speciation??
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Four (broadly accepted) modes of speciation 1)
Allopatric speciation (classical model).2)
Founder effect speciation.3) Peripheral isolates
speciation.4) Genetic hiccups.
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• Allopatric speciation (classical model).
• - A species range is divide geographically by
  some event, dividing the species into sub-groups
  and blocking gene flow.
• - Selection pressures within the sub-groups
  drive them toward dissimilarity, differentiation
  occurs, then eventually the two become
  reproductively isolated.

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Populus nigra.
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- Gene flow is blocked
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- Gene flow is blocked
Adaptation, differentiation, ecotypes,
reproductive isolationspeciation
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• 2) Founder effect model of speciation.
• - Some event leads to a very small population-
  or with plants a single individual, arriving in
  some new location, beyond the range of gene flow.
• - Usually intense selection pressure (and
  inbreeding) commence- the founder population
  diverges quickly and becomes a new species.

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Populus nigra.
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Populus nigra.
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- Gene flow is blocked ( inbreeding intense
selection pressure)
Adaptation, differentiation, ecotypes,
reproductive isolationspeciation
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• 3) Peripheral isolates speciation.
• - Perhaps most common (or constant)
• - Individuals at the edge of a species range are
  isolated from the main body of the range.
• - Gene flow is restricted- Selection intense.
• - Ecotypes (varieties) develop, then
  reproductive isolation, then speciation.

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Puma concolor
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Puma concolor
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Puma concolor
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Puma concolor
Gene flow from the south to the north of this
range is highly restricted
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Puma concolor
Populations on the periphery of this very large
range are differentiating into varieties, moving
(perhaps) toward speciation
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Argentine puma Costa Rican Cougar Eastern
South American cougar North American Cougar
(Puma concolor couguar) includes the previous
subspecies and synonyms arundivaga, aztecus,
browni, californica, coryi, floridana,
hippolestes, improcera, kaibabensis, mayensis,
missoulensis, olympus, oregonensis, schorgeri,
stanleyana, vancouverensis and youngi Northern
South American cougar Southern South American
puma
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Puma concolor
Some populations are already completely isolated
(e.g., Florida)
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4) Genetic hiccup. - Something goes wrong
during the reproductive process. - Some
mutation occurs, or new portion of the genome is
turned on, that cause a wildly different
morphology, or other reproductive isolating
mechanism. - In plants, another hiccup
involves a change in the number of chromosomes.
E.g., reproduction involving two diploid
organisms produces a triploid offspring. (which
then cannot interbreed with the parent
population. - Less well understood, the subject
of much current research.
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Speciation