Speciation from Divergent Evolution

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Speciation from Divergent Evolution
SpeciationThe 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?)
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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.
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How do new species form?
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)
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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 water

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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 reticulata
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Squirrels separated by the Grand Canyon
Abert squirrel South Rim
Kaibab squirrel North Rim
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The story of the Polar Bear...
(Genetic Isolation in a dramatically different
climate)
Ursus arctos
Ursus Maritimus
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Frogs from North America (Mass., Oklahoma,
Arizona)
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Seals originating in the Arctic Sea area
Caspian Seal Phoca caspica (Caspian Sea)
Baikal Phoca sibirica
Seal (Siberia)
Ringed Seal Phoca hispida (hairy)
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Ancestral seal in Arctic ocean pushed southward
during last ice age. When ice retreats
populations are isolated in Lake Baikal and
Caspian Sea
Ringed
Baikal
Lake Baikal is the oldest and deepest lake in the
world.
Only the very extremes of adapted to fresh water
habitats were able to stay and occupy the niches
of the Caspian and Lake Baikal.
Caspian
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Sympatric Speciation (Speciation while in same
geographical area)
It requires Ecological isolation Chromosomal
aberrations
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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 cant breed with diploid plants
and so you have a new species.
It is more common in plants because of asexual
reproduction and self pollination.
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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.
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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

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Warblers and the Spruce Tree
By occupying different niches in the spruce tree
they can reduce competition for food.
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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...

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Cichlid FishLake Victoria Over 300 different
species
Different adaptations to exploit different food
sources in the lake.
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Darwins Finches The Galapagos
But some people think this was allopatric
speciation