“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
(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.
How do new species form?
There are two main mechanisms for speciation:
allopatric speciation (allo = different, patric = fatherland)
sympatric speciation (sym = same)
Two populations are geographical separated from one another.
In different environments natural selection will act differently on each population
Split by some barrier
Different enough to be considered sub-species & given different names
Common GiraffeReticulated Giraffe
Giraffa camelopardalis rothschildi Giraffa camelopardalis reticulata
(Genetic Isolation in a dramatically
Frogs from North America
(Mass., Oklahoma, Arizona)
Seals originating in the Arctic Sea area:
Phoca caspica (Caspian Sea)
Phoca hispida (hairy)
Ancestral seal in Arctic ocean pushed southward during last ice age. When ice retreats populations are isolated in Lake Baikal and Caspian Sea
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.
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.
By occupying different niches in the spruce tree they can reduce competition for food.
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