n1.slideserve.comPPTFilesspeciation_113185_12468 by yurtgc548

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									“Speciation” from Divergent Evolution

Speciation:The process by which two populations
achieve reproductive isolation. (Become new species)


Sure, natural selection can cause the changes within a
species
that we witness in nature:
        Color of moth
        Beak of the Finch
 But can this account for the divergence of animals into
 different
 species, though?

               (by the way, what is a “species?”)
A species: All the organisms that are potentially
capable of interbreeding under natural conditions.

Is a horse and A donkey the same species?
      No, because their offspring (Mule) is sterile.
For new species to form then two factors are important:
   Isolation of populations
       (stopping gene flow between populations)


  Genetic divergence
     (natural selection causes changes in allele frequencies
  so genetic differences mean they can no longer successfully
  breed)
 There are two main mechanisms for speciation:
        allopatric speciation (allo = different, patric =
 fatherland)
        sympatric speciation (sym = same)
Allopatric Speciation:
Two populations are geographical separated
from one another.
In different environments natural selection
will act differently on each population


                   Split by some
                    barrier
                   •   River
                   •   Canyon
                   •   Island
                   •   Mountain
                   •   Different puddles of
Giraffe split by the Tana River in Kenya
Different enough to be considered sub-species & given different
names




Common Giraffe                     Reticulated Giraffe
Giraffa camelopardalis rothschildi        Giraffa camelopardalis
      Squirrels separated by the
            Grand Canyon




Kaibab squirrel     Abert squirrel

North Rim           South Rim
        The story of the Polar Bear...


Ursus arctos     (Genetic Isolation in a dramatically
                 different climate)

                           Ursus Maritimus
 Frogs from North America
(Mass., Oklahoma, Arizona)
   Seals originating in the Arctic Sea area:

                          Caspian Seal
                          Phoca caspica (Caspian Se




Baikal                              Seal
Phoca sibirica                      (Siberia)


  Ringed Seal
  Phoca hispida (hairy)
Ancestral seal in Arctic
ocean pushed southward
during last ice age. When
ice retreats populations are   Ringed
isolated in Lake Baikal and
Caspian Sea                             Baikal

Lake Baikal is the oldest
and deepest lake in the
world.
Only the very extremes
of adapted to fresh water               Caspian
habitats were able to stay
and
occupy the niches of the
Caspian and Lake Baikal.
Sympatric Speciation:
(Speciation while in same
geographical area)

It requires…
   Ecological isolation
   Chromosomal aberrations
Changes in chromosome number can cause immediate
reproductive isolation.

A common form of this in plants is called polyploidy where
the plants have an extra copy of each chromosome.

A tetraploid cell forms (4 sets of each chromosome)
It form gametes with diploid cells and if it reproduces with
other tetrapoids or reproduces asexually it can have viable
offspring.

Tetrapoid plants can’t breed with diploid plants and so
you have a new species.

It is more common in plants because of asexual
reproduction and self pollination.
Disruptive Selection in a population can
lead to Ecological isolation of
populations.
  Different members of the same species may
  begin to specialize in one habitat or another.

 Rhagoletis pomonella used to be a parasite
 of just hawthorn fruit.
 In the last 150 years it has started to divide
 into two species, one that now feeds on
 apples.
 They are becoming genetically isolated and
 genetic differences are appearing.
 Hatching Times vary and mating sites are
 different.
How do they diverge while both
living in the same environment?

• Each organism focuses its existence on
  a different aspect of the environment.

• For example, think vertical: we can
  exist in the same area as a mole,
  mouse, squirrel, bluejay and hawk.
  Each just occupies a different layer of
  the same environment
   Warblers and the Spruce Tree
By occupying different niches in the spruce tree they can reduce
competition for food.
The Warblers are said to be exploiting
different “niches”
• Each niche is made up of a specific type of food
  and/or shelter that an organism can specialize in.
• Even a small environment can sustain many different
  niches.
• For the previous examples, the animals could co-exist
  in the same area by specializing in different aspects of
  that environment.
• Some more examples...
Cichlid Fish:Lake
Victoria
Over 300 different species
Different adaptations to exploit
 different food sources in the lake.
         Darwin’s Finches: The Galapagos



But some
people think
this was
allopatric
speciation

								
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