“Speciation” from Divergent Evolution
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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.

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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?”)


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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...

Ursus arctos

(Genetic Isolation in a dramatically

different climate)

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: ice age. When ice retreats populations are isolated in Lake Baikal and Caspian Sea(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 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.


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Disruptive Selection reproductive isolation. 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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By occupying different niches in the spruce tree they can reduce competition for food.

Warblers and the Spruce Tree


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The Warblers are said to be exploiting different “ reduce competition for food.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 Fish:Lake Victoria reduce competition for food.

Over 300 different species

Different adaptations to exploit different food sources in the lake.


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Darwin’s Finches: The Galapagos reduce competition for food.

But some people think this was allopatric speciation


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